AMD_x86-64_Architecture_Programmers_Manuals

x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a

64-bit In computer architecture, 64-bit Integer (computer science), integers, memory addresses, or other Data (computing), data units are those that are 64 bits wide. Also, 64-bit central processing unit, CPUs and arithmetic logic unit, ALUs are those ...

version of the

x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was introd ...

instruction set In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ' ...

, first released in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level

paging In computer operating systems, memory paging is a memory management scheme by which a computer stores and retrieves data from secondary storage for use in main memory. In this scheme, the operating system retrieves data from secondary storage ...

mode. With 64-bit mode and the new paging mode, it supports vastly larger amounts of

virtual memory In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very l ...

and

physical memory Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processing unit (CPU) of a computer ...

than was possible on its 32-bit predecessors, allowing programs to store larger amounts of data in memory. x86-64 also expands

general-purpose register A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only. ...

s to 64-bit, and expands the number of them from 8 (some of which had limited or fixed functionality, e.g. for stack management) to 16 (fully general), and provides numerous other enhancements.

Floating-point arithmetic In computing, floating-point arithmetic (FP) is arithmetic that represents real numbers approximately, using an integer with a fixed precision, called the significand, scaled by an integer exponent of a fixed base. For example, 12.345 can be ...

is supported via mandatory

SSE2 SSE2 (Streaming SIMD Extensions 2) is one of the Intel SIMD (Single Instruction, Multiple Data) processor supplementary instruction sets first introduced by Intel with the initial version of the Pentium 4 in 2000. It extends the earlier Streamin ...

-like instructions, and

x87 x87 is a floating-point-related subset of the x86 architecture instruction set. It originated as an extension of the 8086 instruction set in the form of optional floating-point coprocessors that worked in tandem with corresponding x86 CPUs. These ...

/ MMX style registers are generally not used (but still available even in 64-bit mode); instead, a set of 16

vector registers A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only. ...

, 128 bits each, is used. (Each register can store one or two

double-precision Double-precision floating-point format (sometimes called FP64 or float64) is a floating-point number format, usually occupying 64 bits in computer memory; it represents a wide dynamic range of numeric values by using a floating radix point. Flo ...

numbers or one to four

single-precision Single-precision floating-point format (sometimes called FP32 or float32) is a computer number format, usually occupying 32 bits in computer memory; it represents a wide dynamic range of numeric values by using a floating radix point. A floating- ...

numbers, or various integer formats.) In 64-bit mode, instructions are modified to support 64-bit

operands In mathematics, an operand is the object of a mathematical operation, i.e., it is the object or quantity that is operated on. Example The following arithmetic expression shows an example of operators and operands: :3 + 6 = 9 In the above exampl ...

and 64-bit

addressing mode Addressing modes are an aspect of the instruction set architecture in most central processing unit (CPU) designs. The various addressing modes that are defined in a given instruction set architecture define how the machine language instructions in ...

. The compatibility mode defined in the architecture allows 16- and 32-bit user applications to run unmodified, coexisting with 64-bit applications if the 64-bit operating system supports them. As the full x86 16-bit and 32-bit instruction sets remain implemented in hardware without any intervening emulation, these older

executable In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instruction (computer science), instructi ...

s can run with little or no performance penalty, while newer or modified applications can take advantage of new features of the processor design to achieve performance improvements. Also, a processor supporting x86-64 still powers on in

real mode Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20-bit seg ...

for full

backward compatibility Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially i ...

with the

8086 The 8086 (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus (allowi ...

, as x86 processors supporting

protected mode In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking d ...

have done since the

80286 The Intel 80286 (also marketed as the iAPX 286 and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non-multiplexed address and data buses and also the fi ...

. The original specification, created by

AMD Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufactur ...

and released in 2000, has been implemented by AMD,

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...

, and

VIA Via or VIA may refer to the following: Science and technology * MOS Technology 6522, Versatile Interface Adapter * ''Via'' (moth), a genus of moths in the family Noctuidae * Via (electronics), a through-connection * VIA Technologies, a Taiwan ...

. The

AMD K8 The AMD K8 Hammer, also code-named SledgeHammer, is a computer processor microarchitecture designed by AMD as the successor to the AMD K7 Athlon microarchitecture. The K8 was the first implementation of the AMD64 64-bit extension to the x86 ins ...

microarchitecture In computer engineering, microarchitecture, also called computer organization and sometimes abbreviated as µarch or uarch, is the way a given instruction set architecture (ISA) is implemented in a particular processor. A given ISA may be impl ...

, in the

Opteron Opteron is AMD's x86 former server and workstation processor line, and was the first processor which supported the AMD64 instruction set architecture (known generically as x86-64 or AMD64). It was released on April 22, 2003, with the ''SledgeHa ...

and

Athlon 64 The Athlon 64 is a ninth-generation, AMD64-architecture microprocessor produced by Advanced Micro Devices (AMD), released on September 23, 2003. It is the third processor to bear the name ''Athlon'', and the immediate successor to the Athlon XP. T ...

processors, was the first to implement it. This was the first significant addition to the

architecture designed by a company other than Intel. Intel was forced to follow suit and introduced a modified

NetBurst The NetBurst microarchitecture, called P68 inside Intel, was the successor to the P6 microarchitecture in the x86 family of central processing units (CPUs) made by Intel. The first CPU to use this architecture was the Willamette-core Pentium 4 ...

family which was software-compatible with AMD's specification.

VIA Technologies VIA Technologies Inc. (), is a Taiwanese manufacturer of integrated circuits, mainly motherboard chipsets, CPUs, and memory. It was the world's largest independent manufacturer of motherboard chipsets. As a fabless semiconductor company, VIA c ...

introduced x86-64 in their VIA Isaiah architecture, with the

VIA Nano The VIA Nano (formerly Code name#Commercial code names in the computer industry, code-named VIA Isaiah) is a 64-bit CPU for personal computers. The VIA Nano was released by VIA Technologies in 2008 after five years of development by its CPU divi ...

. The x86-64 architecture is distinct from the Intel

Itanium Itanium ( ) is a discontinued family of 64-bit Intel microprocessors that implement the Intel Itanium architecture (formerly called IA-64). Launched in June 2001, Intel marketed the processors for enterprise servers and high-performance computin ...

architecture (formerly

IA-64 IA-64 (Intel Itanium architecture) is the instruction set architecture (ISA) of the Itanium family of 64-bit Intel microprocessors. The basic ISA specification originated at Hewlett-Packard (HP), and was subsequently implemented by Intel in coll ...

). The architectures are not compatible on the native instruction set level, and operating systems and applications compiled for one cannot be run on the other.

AMD64

History

AMD64 (also variously referred to by

in their literature and documentation as “AMD 64-bit Technology” and “AMD x86-64 Architecture”) was created as an alternative to the radically different

architecture designed by

and

Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...

, which was

backward-incompatible Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially i ...

with

IA-32 IA-32 (short for "Intel Architecture, 32-bit", commonly called i386) is the 32-bit version of the x86 instruction set architecture, designed by Intel and first implemented in the 80386 microprocessor in 1985. IA-32 is the first incarnation of ...

, the 32-bit version of the

architecture. AMD originally announced AMD64 in 1999 with a full specification available in August 2000. As AMD was never invited to be a contributing party for the IA-64 architecture and any kind of licensing seemed unlikely, the AMD64 architecture was positioned by AMD from the beginning as an evolutionary way to add

64-bit computing In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs are those that are based on processor registers, address buses, or data buses of that size. A compute ...

capabilities to the existing x86 architecture while supporting legacy 32-bit x86

code In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communication ...

, as opposed to Intel's approach of creating an entirely new, completely x86-incompatible 64-bit architecture with IA-64. The first AMD64-based processor, the

, was released in April 2003.

Implementations

AMD's processors implementing the AMD64 architecture include

Athlon 64 X2 The Athlon 64 X2 is the first native dual-core desktop central processing unit (CPU) designed by Advanced Micro Devices (AMD). It was designed from scratch as native dual-core by using an already multi-CPU enabled Athlon 64, joining it with anoth ...

Athlon 64 FX The Athlon 64 is a ninth-generation, AMD64-architecture microprocessor produced by Advanced Micro Devices (AMD), released on September 23, 2003. It is the third processor to bear the name ''Athlon'', and the immediate successor to the Athlon XP. T ...

Athlon II Athlon II is a family of AMD multi-core 45 nm central processing units, which is aimed at the budget to mid-range market and is a complementary product lineup to the Phenom II. Features The Athlon II series is based on the AMD K10 architectu ...

(followed by "X2", "X3", or "X4" to indicate the number of cores, and XLT models),

Turion 64 AMD Turion is the brand name AMD applies to its x86-64 low-power consumption (''mobile'') processors codenamed ''K8L''. The Turion 64 and Turion 64 X2/Ultra processors compete with Intel's mobile processors, initially the '' Pentium M'' and the I ...

Turion 64 X2 AMD Turion is the brand name AMD applies to its x86-64 low-power consumption (''mobile'') processors codenamed ''K8L''. The Turion 64 and Turion 64 X2/Ultra processors compete with Intel's mobile processors, initially the ''Pentium M'' and the Int ...

Sempron Sempron has been the marketing name used by AMD for several different budget desktop CPUs, using several different technologies and CPU socket formats. The Sempron replaced the AMD Duron processor and competed against Intel's Celeron series of pr ...

("Palermo" E6 stepping and all "Manila" models),

Phenom Phenom may refer to: * AMD Phenom, the 64-bit AMD desktop processor line based on the K10 microarchitecture ** Phenom II, a family of AMD's multi-core 45 nm processors using the AMD K10 microarchitecture * Phenom (electron microscope), a fast elec ...

(followed by "X3" or "X4" to indicate the number of cores),

Phenom II Phenom II is a family of AMD's multi-core 45 nm processors using the AMD K10 microarchitecture, succeeding the original Phenom. Advanced Micro Devices released the Socket AM2+ version of Phenom II in December 2008, while Socket AM3 versions w ...

(followed by "X2", "X3", "X4" or "X6" to indicate the number of cores), FX, Fusion/APU and

Ryzen Ryzen ( ) is a brand of multi-core x86-64 microprocessors designed and marketed by AMD for desktop, mobile, server, and embedded platforms based on the Zen microarchitecture. It consists of central processing units (CPUs) marketed for mainst ...

Epyc Epyc is a brand of multi-core x86-64 microprocessors designed and sold by AMD, based on the company's Zen microarchitecture. Introduced in June 2017, they are specifically targeted for the server and embedded system markets. Epyc processors share t ...

Architectural features

The primary defining characteristic of AMD64 is the availability of 64-bit general-purpose

processor register A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only. ...

s (for example, ), 64-bit

integer An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign (−1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the language ...

arithmetic and logical operations, and 64-bit virtual addresses. The designers took the opportunity to make other improvements as well. Notable changes in the 64-bit extensions include: ; 64-bit integer capability : All

s (GPRs) are expanded from 32

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...

s to 64 bits, and all arithmetic and logical operations, memory-to-register and register-to-memory operations, etc., can operate directly on 64-bit integers. Pushes and pops on the

stack Stack may refer to: Places * Stack Island, an island game reserve in Bass Strait, south-eastern Australia, in Tasmania’s Hunter Island Group * Blue Stack Mountains, in Co. Donegal, Ireland People * Stack (surname) (including a list of people ...

default to 8-byte strides, and

pointers Pointer may refer to: Places * Pointer, Kentucky * Pointers, New Jersey * Pointers Airport, Wasco County, Oregon, United States * The Pointers, a pair of rocks off Antarctica People with the name * Pointer (surname), a surname (including a l ...

are 8 bytes wide. ; Additional registers : In addition to increasing the size of the general-purpose registers, the number of named general-purpose registers is increased from eight (i.e. , , , , , , , ) in x86 to 16 (i.e. , , , , , , , , , , , , , , , ). It is therefore possible to keep more local variables in registers rather than on the stack, and to let registers hold frequently accessed constants; arguments for small and fast subroutines may also be passed in registers to a greater extent. : AMD64 still has fewer registers than many

RISC In computer engineering, a reduced instruction set computer (RISC) is a computer designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a complex instruction set comput ...

s (e.g.

PA-RISC PA-RISC is an instruction set architecture (ISA) developed by Hewlett-Packard. As the name implies, it is a reduced instruction set computer (RISC) architecture, where the PA stands for Precision Architecture. The design is also referred to as ...

Power ISA Power ISA is a reduced instruction set computer (RISC) instruction set architecture (ISA) currently developed by the OpenPOWER Foundation, led by IBM. It was originally developed by IBM and the now-defunct Power.org industry group. Power IS ...

, and MIPS have 32 GPRs;

Alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...

, 64-bit ARM, and

SPARC SPARC (Scalable Processor Architecture) is a reduced instruction set computer (RISC) instruction set architecture originally developed by Sun Microsystems. Its design was strongly influenced by the experimental Berkeley RISC system developed ...

have 31) or

VLIW Very long instruction word (VLIW) refers to instruction set architectures designed to exploit instruction level parallelism (ILP). Whereas conventional central processing units (CPU, processor) mostly allow programs to specify instructions to exe ...

-like machines such as the

(which has 128 registers). However, an AMD64 implementation may have far more internal registers than the number of architectural registers exposed by the instruction set (see

register renaming In computer architecture, register renaming is a technique that abstracts logical registers from physical registers. Every logical register has a set of physical registers associated with it. When a machine language instruction refers to a particu ...

). (For example, AMD Zen cores have 168 64-bit integer and 160 128-bit vector floating-point physical internal registers.) ; Additional XMM (SSE) registers : Similarly, the number of 128-bit XMM registers (used for Streaming SIMD instructions) is also increased from 8 to 16. : The traditional x87 FPU register stack is not included in the register file size extension in 64-bit mode, compared with the XMM registers used by SSE2, which did get extended. The

register stack is not a simple register file although it does allow direct access to individual registers by low cost exchange operations. ; Larger virtual address space : The AMD64 architecture defines a 64-bit virtual address format, of which the low-order 48 bits are used in current implementations. This allows up to 256 TB (2⁴⁸

byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...

s) of virtual address space. The architecture definition allows this limit to be raised in future implementations to the full 64 bits, extending the virtual address space to 16 EB (2⁶⁴ bytes). This is compared to just 4 GB (2³² bytes) for the x86. :This means that very large files can be operated on by mapping the entire file into the process's address space (which is often much faster than working with file read/write calls), rather than having to map regions of the file into and out of the address space. ; Larger physical address space : The original implementation of the AMD64 architecture implemented 40-bit

physical address In computing, a physical address (also real address, or binary address), is a memory address that is represented in the form of a binary number on the address bus circuitry in order to enable the data bus to access a ''particular'' storage cell o ...

es and so could address up to 1 TB (2⁴⁰ bytes) of RAM. Current implementations of the AMD64 architecture (starting from AMD 10h microarchitecture) extend this to 48-bit physical addresses and therefore can address up to 256 TB (2⁴⁸ bytes) of RAM. The architecture permits extending this to 52 bits in the future (limited by the page table entry format); this would allow addressing of up to 4 PB of RAM. For comparison, 32-bit x86 processors are limited to 64 GB of RAM in

Physical Address Extension In computing, Physical Address Extension (PAE), sometimes referred to as Page Address Extension, is a memory management feature for the x86 architecture. PAE was first introduced by Intel in the Pentium Pro, and later by AMD in the Athlon process ...

(PAE) mode, or 4 GB of RAM without PAE mode. ; Larger physical address space in legacy mode : When operating in

legacy mode In computing, legacy mode is a state in which a computer system, component, or software application behaves in a way that is different from its standard operation in order to support older software, data, or expected behavior. It differs from backw ...

the AMD64 architecture supports

(PAE) mode, as do most current x86 processors, but AMD64 extends PAE from 36 bits to an architectural limit of 52 bits of physical address. Any implementation, therefore, allows the same physical address limit as under

long mode In the x86-64 computer architecture, long mode is the mode where a 64-bit operating system can access 64-bit instructions and registers. 64-bit programs are run in a sub-mode called 64-bit mode, while 32-bit programs and 16-bit protected mode pr ...

. ; Instruction pointer relative data access : Instructions can now reference data relative to the instruction pointer (RIP register). This makes

position-independent code In computing, position-independent code (PIC) or position-independent executable (PIE) is a body of machine code that, being placed somewhere in the primary memory, executes properly regardless of its absolute address. PIC is commonly used for ...

, as is often used in

shared libraries In computer science, a library is a collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and subr ...

and code loaded at run time, more efficient. ; SSE instructions : The original AMD64 architecture adopted Intel's SSE and

as core instructions. These instruction sets provide a vector supplement to the scalar

FPU, for the single-precision and double-precision data types. SSE2 also offers integer vector operations, for data types ranging from 8bit to 64bit precision. This makes the vector capabilities of the architecture on par with those of the most advanced x86 processors of its time. These instructions can also be used in 32-bit mode. The proliferation of 64-bit processors has made these vector capabilities ubiquitous in home computers, allowing the improvement of the standards of 32-bit applications. The 32-bit edition of Windows 8, for example, requires the presence of SSE2 instructions.

SSE3 SSE3, Streaming SIMD Extensions 3, also known by its Intel code name Prescott New Instructions (PNI), is the third iteration of the SSE instruction set for the IA-32 (x86) architecture. Intel introduced SSE3 in early 2004 with the Prescott revis ...

instructions and later

Streaming SIMD Extensions In computing, Streaming SIMD Extensions (SSE) is a single instruction, multiple data (SIMD) instruction set extension to the x86 architecture, designed by Intel and introduced in 1999 in their Pentium III series of Central processing units (CPUs) ...

instruction sets are not standard features of the architecture. ; No-Execute bit : The No-Execute bit or

NX bit The NX bit (no-execute) is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions or for storage of data, a feature normally only found in Harvard architecture processors. However, the NX bit is ...

(bit 63 of the page table entry) allows the operating system to specify which pages of virtual address space can contain executable code and which cannot. An attempt to execute code from a page tagged "no execute" will result in a memory access violation, similar to an attempt to write to a read-only page. This should make it more difficult for malicious code to take control of the system via "

buffer overrun In information security and programming, a buffer overflow, or buffer overrun, is an anomaly whereby a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory locations. Buffers are areas of memor ...

" or "unchecked buffer" attacks. A similar feature has been available on x86 processors since the

as an attribute of

segment descriptor In memory addressing for Intel x86 computer architectures, segment descriptors are a part of the segmentation unit, used for translating a logical address to a linear address. Segment descriptors describe the memory segment referred to in the logic ...

s; however, this works only on an entire segment at a time. : Segmented addressing has long been considered an obsolete mode of operation, and all current PC operating systems in effect bypass it, setting all segments to a base address of zero and (in their 32-bit implementation) a size of 4 GB. AMD was the first x86-family vendor to implement no-execute in linear addressing mode. The feature is also available in legacy mode on AMD64 processors, and recent Intel x86 processors, when PAE is used. ; Removal of older features : A few "system programming" features of the x86 architecture were either unused or underused in modern operating systems and are either not available on AMD64 in long (64-bit and compatibility) mode, or exist only in limited form. These include segmented addressing (although the FS and GS segments are retained in vestigial form for use as extra-base pointers to operating system structures), the task state switch mechanism, and

virtual 8086 mode In the 80386 microprocessor and later, virtual 8086 mode (also called virtual real mode, V86-mode, or VM86) allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is runnin ...

. These features remain fully implemented in "legacy mode", allowing these processors to run 32-bit and 16-bit operating systems without modifications. Some instructions that proved to be rarely useful are not supported in 64-bit mode, including saving/restoring of segment registers on the stack, saving/restoring of all registers (PUSHA/POPA), decimal arithmetic, BOUND and INTO instructions, and "far" jumps and calls with immediate operands.

Virtual address space details

Canonical form addresses

Although virtual addresses are 64 bits wide in 64-bit mode, current implementations (and all chips that are known to be in the planning stages) do not allow the entire virtual address space of 2⁶⁴ bytes (16 EB) to be used. This would be approximately four billion times the size of the virtual address space on 32-bit machines. Most operating systems and applications will not need such a large address space for the foreseeable future, so implementing such wide virtual addresses would simply increase the complexity and cost of address translation with no real benefit. AMD, therefore, decided that, in the first implementations of the architecture, only the least significant 48 bits of a virtual address would actually be used in address translation (

page table A page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses. Virtual addresses are used by the program executed by the accessing process, ...

lookup). In addition, the AMD specification requires that the most significant 16 bits of any virtual address, bits 48 through 63, must be copies of bit 47 (in a manner akin to

sign extension Sign extension (abbreviated as sext) is the operation, in computer arithmetic, of increasing the number of bits of a binary number while preserving the number's sign (positive/negative) and value. This is done by appending digits to the most signi ...

). If this requirement is not met, the processor will raise an exception. Addresses complying with this rule are referred to as "canonical form." Canonical form addresses run from 0 through 00007FFF'FFFFFFFF, and from FFFF8000'00000000 through FFFFFFFF'FFFFFFFF, for a total of 256 TB of usable virtual address space. This is still 65,536 times larger than the virtual 4 GB address space of 32-bit machines. This feature eases later scalability to true 64-bit addressing. Many operating systems (including, but not limited to, the

Windows NT Windows NT is a proprietary graphical operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems sc ...

family) take the higher-addressed half of the address space (named

kernel space A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel ...

) for themselves and leave the lower-addressed half (

user space A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel ...

) for application code, user mode stacks, heaps, and other data regions. The "canonical address" design ensures that every AMD64 compliant implementation has, in effect, two memory halves: the lower half starts at 00000000'00000000 and "grows upwards" as more virtual address bits become available, while the higher half is "docked" to the top of the address space and grows downwards. Also, enforcing the "canonical form" of addresses by checking the unused address bits prevents their use by the operating system in

tagged pointer In computer science, a tagged pointer is a pointer (concretely a memory address) with additional data associated with it, such as an indirection bit or reference count. This additional data is often "folded" into the pointer, meaning stored inline ...

s as flags, privilege markers, etc., as such use could become problematic when the architecture is extended to implement more virtual address bits. The first versions of Windows for x64 did not even use the full 256 TB; they were restricted to just 8 TB of user space and 8 TB of kernel space. Windows did not support the entire 48-bit address space until Windows 8.1, which was released in October 2013.

Page table structure

The 64-bit addressing mode ("

") is a superset of

s (PAE); because of this,

page Page most commonly refers to: * Page (paper), one side of a leaf of paper, as in a book Page, PAGE, pages, or paging may also refer to: Roles * Page (assistance occupation), a professional occupation * Page (servant), traditionally a young mal ...

sizes may be 4 KB (2¹² bytes) or 2 MB (2²¹ bytes). Long mode also supports page sizes of 1 GB (2³⁰ bytes). Rather than the three-level

system used by systems in PAE mode, systems running in

use four levels of page table: PAE's ''Page-Directory Pointer Table'' is extended from four entries to 512, and an additional ''Page-Map Level 4 (PML4) Table'' is added, containing 512 entries in 48-bit implementations. A full mapping hierarchy of 4 KB pages for the whole 48-bit space would take a bit more than 512 GB of memory (about 0.195% of the 256 TB virtual space). Intel has implemented a scheme with a 5-level page table, which allows Intel 64 processors to support a 57-bit virtual address space. Further extensions may allow full 64-bit virtual address space and physical memory by expanding the page table entry size to 128-bit, and reduce page walks in the 5-level hierarchy by using a larger 64 KB page allocation size that still supports 4 KB page operations for backward compatibility.

Operating system limits

The operating system can also limit the virtual address space. Details, where applicable, are given in the " Operating system compatibility and characteristics" section.

Physical address space details

Current AMD64 processors support a physical address space of up to 2⁴⁸ bytes of RAM, or 256 TB. However, , there were no known x86-64

motherboard A motherboard (also called mainboard, main circuit board, mb, mboard, backplane board, base board, system board, logic board (only in Apple computers) or mobo) is the main printed circuit board (PCB) in general-purpose computers and other expand ...

s that support 256 TB of RAM. The operating system may place additional limits on the amount of RAM that is usable or supported. Details on this point are given in the " Operating system compatibility and characteristics" section of this article.

Operating modes

The architecture has two primary modes of operation: long mode and legacy mode. AMD64StateDiagram

Long mode

Long mode is the architecture's intended primary mode of operation; it is a combination of the processor's native 64-bit mode and a combined 32-bit and 16-bit compatibility mode. It is used by 64-bit operating systems. Under a 64-bit operating system, 64-bit programs run under 64-bit mode, and 32-bit and 16-bit protected mode applications (that do not need to use either real mode or virtual 8086 mode in order to execute at any time) run under compatibility mode. Real-mode programs and programs that use virtual 8086 mode at any time cannot be run in long mode unless those modes are emulated in software. However, such programs may be started from an operating system running in long mode on processors supporting

VT-x x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-as ...

AMD-V x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-as ...

by creating a virtual processor running in the desired mode. Since the basic

is the same, there is almost no performance penalty for executing protected mode x86 code. This is unlike Intel's

, where differences in the underlying instruction set mean that running 32-bit code must be done either in emulation of x86 (making the process slower) or with a dedicated x86 coprocessor. However, on the x86-64 platform, many x86 applications could benefit from a 64-bit

recompile In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...

, due to the additional registers in 64-bit code and guaranteed SSE2-based FPU support, which a

compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...

can use for optimization. However, applications that regularly handle integers wider than 32 bits, such as cryptographic algorithms, will need a rewrite of the code handling the huge integers in order to take advantage of the 64-bit registers.

Legacy mode

Legacy mode is the mode that the processor is in when it is not in long mode. In this mode, the processor acts like an older x86 processor, and only 16-bit and 32-bit code can be executed. Legacy mode allows for a maximum of 32 bit virtual addressing which limits the virtual address space to 4 GB. 64-bit programs cannot be run from legacy mode.

= Protected mode

Protected mode In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking d ...

is made into a submode of legacy mode. It is the submode that 32-bit operating systems and 16-bit protected mode operating systems operate in when running on an x86-64 CPU.

= Real mode

Real mode Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20-bit seg ...

is the initial mode of operation when the processor is initialized, and is a submode of legacy mode. It is backwards compatible with the original

Intel 8086 The 8086 (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus (allowi ...

and

Intel 8088 The Intel 8088 ("''eighty-eighty-eight''", also called iAPX 88) microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 has an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers an ...

processors. Real mode is primarily used today by operating system bootloaders, which are required by the architecture to configure virtual memory details before transitioning to higher modes. This mode is also used by any operating system that needs to communicate with the system firmware with a traditional

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...

-style interface.

Intel 64

Intel 64 is Intel's implementation of x86-64, used and implemented in various processors made by Intel.

History

Historically, AMD has developed and produced processors with instruction sets patterned after Intel's original designs, but with x86-64, roles were reversed: Intel found itself in the position of adopting the

ISA Isa or ISA may refer to: Places * Isa, Amur Oblast, Russia * Isa, Kagoshima, Japan * Isa, Nigeria * Isa District, Kagoshima, former district in Japan * Isa Town, middle class town located in Bahrain * Mount Isa, Queensland, Australia * Mount Is ...

that AMD created as an extension to Intel's own x86 processor line. Intel's project was originally

codename A code name, call sign or cryptonym is a Code word (figure of speech), code word or name used, sometimes clandestinely, to refer to another name, word, project, or person. Code names are often used for military purposes, or in espionage. They may ...

d ''Yamhill'' (after the

Yamhill River The Yamhill River is an tributary of the Willamette River, in the U.S. state of Oregon. Formed by the confluence of the South Yamhill River and the North Yamhill River about east of McMinnville, it drains part of the Northern Oregon Coast Rang ...

in Oregon's Willamette Valley). After several years of denying its existence, Intel announced at the February 2004

IDF IDF or idf may refer to: Defence forces * Irish Defence Forces * Israel Defense Forces *Iceland Defense Force, of the US Armed Forces, 1951-2006 * Indian Defence Force, a part-time force, 1917 Organizations * Israeli Diving Federation * Interac ...

that the project was indeed underway. Intel's chairman at the time, Craig Barrett, admitted that this was one of their worst-kept secrets. Intel's name for this instruction set has changed several times. The name used at the IDF was ''CT'' (presumably for ''Clackamas Technology'', another codename from an Oregon river); within weeks they began referring to it as ''IA-32e'' (for

extensions) and in March 2004 unveiled the "official" name ''EM64T'' (Extended Memory 64 Technology). In late 2006 Intel began instead using the name ''Intel 64'' for its implementation, paralleling AMD's use of the name AMD64. The first processor to implement Intel 64 was the multi-socket processor

Xeon Xeon ( ) is a brand of x86 microprocessors designed, manufactured, and marketed by Intel, targeted at the non-consumer workstation, server, and embedded system markets. It was introduced in June 1998. Xeon processors are based on the same arc ...

code-named '' Nocona'' in June 2004. In contrast, the initial Prescott chips (February 2004) did not enable this feature. Intel subsequently began selling Intel 64-enabled Pentium 4s using the E0 revision of the Prescott core, being sold on the OEM market as the Pentium 4, model F. The E0 revision also adds eXecute Disable (XD) (Intel's name for the

) to Intel 64, and has been included in then current Xeon code-named ''Irwindale''. Intel's official launch of Intel 64 (under the name EM64T at that time) in mainstream desktop processors was the N0 stepping Prescott-2M. The first Intel

mobile processor A mobile processor is found in mobile computers and cellphones. A CPU chip is designed for portable computers to run fanless, under 10-15W, which is cool enough without a fan. It is typically housed in a smaller chip package, but more important ...

implementing Intel 64 is the Merom version of the

Core 2 Intel Core 2 is the processor family encompassing a range of Intel's consumer 64-bit x86-64 single-, dual-, and quad-core microprocessors based on the Core microarchitecture. The single- and dual-core models are single- die, whereas the quad-cor ...

processor, which was released on July 27, 2006. None of Intel's earlier notebook CPUs (

Core Duo Intel Core is a line of streamlined midrange consumer, workstation and enthusiast computer central processing units (CPUs) marketed by Intel Corporation. These processors displaced the existing mid- to high-end Pentium processors at the time ...

Pentium M The Pentium M is a family of mobile 32-bit single-core x86 microprocessors (with the modified Intel P6 microarchitecture) introduced in March 2003 and forming a part of the Intel Carmel notebook platform under the then new Centrino brand. The '' ...

Celeron M Celeron is Intel's brand name for low-end IA-32 and x86-64 computer microprocessor models targeted at low-cost personal computers. Celeron processors are compatible with IA-32 software. They typically offer less performance per clock speed ...

, Mobile Pentium 4) implement Intel 64.

Implementations

Intel's processors implementing the Intel64 architecture include the

Pentium 4 Pentium 4 is a series of single-core CPUs for desktops, laptops and entry-level servers manufactured by Intel. The processors were shipped from November 20, 2000 until August 8, 2008. The production of Netburst processors was active from 2000 ...

F-series/5x1 series, 506, and 516,

Celeron D Celeron is Intel's brand name for low-end IA-32 and x86-64 computer microprocessor models targeted at low-cost personal computers. Celeron processors are compatible with IA-32 software. They typically offer less performance per clock speed comp ...

models 3x1, 3x6, 355, 347, 352, 360, and 365 and all later

Celeron Celeron is Intel's brand name for low-end IA-32 and x86-64 computer microprocessor models targeted at low-cost personal computers. Celeron processors are compatible with IA-32 IA-32 (short for "Intel Architecture, 32-bit", commonly called ...

s, all models of

since " Nocona", all models of

Pentium Dual-Core The Pentium Dual-Core brand was used for mainstream x86-architecture microprocessors from Intel from 2006 to 2009 when it was renamed to Pentium. The processors are based on either the 32-bit '' Yonah'' or (with quite different microarchitectur ...

processors since " Merom-2M", the

Atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, and ...

230, 330, D410, D425, D510, D525, N450, N455, N470, N475, N550, N570, N2600 and N2800, all versions of the

Pentium D Pentium D is a range of desktop 64-bit x86-64 processors based on the NetBurst microarchitecture, which is the dual-core variant of the Pentium 4 manufactured by Intel. Each CPU comprised two dies, each containing a single core, residing next to ...

Pentium Extreme Edition Pentium D is a range of desktop 64-bit x86-64 processors based on the NetBurst microarchitecture, which is the dual-core variant of the Pentium 4 manufactured by Intel. Each CPU comprised two dies, each containing a single core, residing next to ...

, Core i9, Core i7, Core i5, and Core i3 processors, and the

Xeon Phi Xeon Phi was a series of x86 manycore processors designed and made by Intel. It was intended for use in supercomputers, servers, and high-end workstations. Its architecture allowed use of standard programming languages and application programmi ...

7200 series processors.

VIA's x86-64 implementation

introduced their first implementation of the x86-64 architecture in 2008 after five years of development by its CPU division,

Centaur Technology Centaur Technology is an x86 CPU design company started in 1995 and subsequently a wholly owned subsidiary of VIA Technologies. In 2015, the documentary ''Rise of the Centaur'' covered the early history of the company. History Centaur Technolog ...

. Codenamed "Isaiah", the 64-bit architecture was unveiled on January 24, 2008, and launched on May 29 under the

brand name. The processor supports a number of VIA-specific x86 extensions designed to boost efficiency in low-power appliances. It is expected that the Isaiah architecture will be twice as fast in integer performance and four times as fast in

floating-point In computing, floating-point arithmetic (FP) is arithmetic that represents real numbers approximately, using an integer with a fixed precision, called the significand, scaled by an integer exponent of a fixed base. For example, 12.345 can b ...

performance as the previous-generation

VIA Esther The VIA C7 is an x86 central processing unit designed by Centaur Technology and sold by VIA Technologies. Product history The C7 delivers a number of improvements to the older VIA C3 cores but is nearly identical to the latest VIA C3 Nehemiah c ...

at an equivalent

clock speed In computing, the clock rate or clock speed typically refers to the frequency at which the clock generator of a processor can generate pulses, which are used to synchronize the operations of its components, and is used as an indicator of the pr ...

. Power consumption is also expected to be on par with the previous-generation VIA CPUs, with

thermal design power The thermal design power (TDP), sometimes called thermal design point, is the maximum amount of heat generated by a computer chip or component (often a CPU, GPU or system on a chip) that the cooling system in a computer is designed to dissipate ...

ranging from 5 W to 25 W. Being a completely new design, the Isaiah architecture was built with support for features like the x86-64 instruction set and

x86 virtualization x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-as ...

which were unavailable on its predecessors, the

VIA C7 The VIA C7 is an x86 central processing unit designed by Centaur Technology and sold by VIA Technologies. Product history The C7 delivers a number of improvements to the older VIA C3 cores but is nearly identical to the latest VIA C3 Nehemiah ...

line, while retaining their encryption extensions.

Microarchitecture levels

In 2020, through a collaboration between AMD, Intel, Red Hat, and SUSE, three microarchitecture levels on top of the x86-64 baseline were defined: x86-64-v2, x86-64-v3, and x86-64-v4. These levels define specific features that can be targeted by programmers to provide compile-time optimizations. The features exposed by each level are as follows: All levels include features found in the previous levels. Instruction set extensions not concerned with general-purpose computation, including

AES-NI An Advanced Encryption Standard instruction set is now integrated into many processors. The purpose of the instruction set is to improve the speed and security of applications performing encryption and decryption using Advanced Encryption Standard ...

and

RDRAND RDRAND (for "read random"; known as Intel Secure Key Technology, previously known as Bull Mountain) is an instruction for returning random numbers from an Intel on-chip hardware random number generator which has been seeded by an on-chip entropy s ...

, are excluded from the level requirements.

Differences between AMD64 and Intel 64

Although nearly identical, there are some differences between the two instruction sets in the semantics of a few seldom used machine instructions (or situations), which are mainly used for

system programming Systems programming, or system programming, is the activity of programming computer system software. The primary distinguishing characteristic of systems programming when compared to application programming is that application programming aims to pr ...

. Compilers generally produce

s (i.e.

machine code In computer programming, machine code is any low-level programming language, consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a very ...

) that avoid any differences, at least for ordinary application programs. This is therefore of interest mainly to developers of compilers, operating systems and similar, which must deal with individual and special system instructions.

Recent implementations

* Intel 64's BSF and BSR instructions act differently than AMD64's when the source is zero and the operand size is 32 bits. The processor sets the zero flag and leaves the upper 32 bits of the destination undefined. Note that Intel documents that the destination register has an undefined value in this case, but in practice in silicon implements the same behaviour as AMD (destination unmodified). The separate claim about maybe not preserving bits in the upper 32 hasn't been verified, but has only been ruled out for Core 2 and Skylake, not all Intel microarchitectures like 64-bit Pentium 4 or low-power Atom. * AMD64 requires a different microcode update format and control MSRs (model-specific registers) while Intel 64 implements

microcode In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a laye ...

update unchanged from their 32-bit only processors. * Intel 64 lacks some MSRs that are considered architectural in AMD64. These include SYSCFG, TOP_MEM, and TOP_MEM2. * Intel 64 allows SYSCALL/SYSRET only in 64-bit mode (not in compatibility mode), and allows SYSENTER/SYSEXIT in both modes. AMD64 lacks SYSENTER/SYSEXIT in both sub-modes of

. * In 64-bit mode, near branches with the 66H (operand size override) prefix behave differently. Intel 64 ignores this prefix: the instruction has 32-bit sign extended offset, and instruction pointer is not truncated. AMD64 uses 16-bit offset field in the instruction, and clears the top 48 bits of instruction pointer. * AMD processors raise a floating-point Invalid Exception when performing an FLD or FSTP of an 80-bit signalling NaN, while Intel processors do not. * Intel 64 lacks the ability to save and restore a reduced (and thus faster) version of the

state (involving the FXSAVE and FXRSTOR instructions). * AMD processors ever since

Rev. E and

Rev. D have reintroduced limited support for segmentation, via the Long Mode Segment Limit Enable (LMSLE) bit, to ease

virtualization In computing, virtualization or virtualisation (sometimes abbreviated v12n, a numeronym) is the act of creating a virtual (rather than actual) version of something at the same abstraction level, including virtual computer hardware platforms, stor ...

of 64-bit guests. * When returning to a non-canonical address using SYSRET, AMD64 processors execute the general protection fault handler in privilege level 3, while on Intel 64 processors it is executed in privilege level 0.

Older implementations

* The AMD64 processors prior to the Revision F (distinguished by the switch from

DDR DDR or ddr may refer to: *ddr, ISO 639-3 code for the Dhudhuroa language *DDr., title for a double doctorate in Germany *DDR, station code for Dadar railway station, Mumbai, India *' (German Democratic Republic), official name of the former East ...

to DDR2 memory and new sockets

AM2 AM2 can refer to: * Socket AM2, a CPU socket for AMD desktop processors * Sega AM2, a research and development team for the video game company Sega * Arp-Madore 2, an open star cluster * a fictional element from The Sten Chronicles * Animusic * AM ...

, F and S1) of 2006 lacked the CMPXCHG16B instruction, which is an extension of the CMPXCHG8B instruction present on most post-

80486 The Intel 486, officially named i486 and also known as 80486, is a microprocessor. It is a higher-performance follow-up to the Intel 386. The i486 was introduced in 1989. It represents the fourth generation of binary compatible CPUs following the ...

processors. Similar to CMPXCHG8B, CMPXCHG16B allows for

atomic operation In concurrent programming, an operation (or set of operations) is linearizable if it consists of an ordered list of invocation and response events (event), that may be extended by adding response events such that: # The extended list can be re-e ...

s on octa-words (128-bit values). This is useful for parallel algorithms that use

compare and swap In computer science, compare-and-swap (CAS) is an atomic instruction used in multithreading to achieve synchronization. It compares the contents of a memory location with a given value and, only if they are the same, modifies the contents of tha ...

on data larger than the size of a pointer, common in

lock-free and wait-free algorithms In computer science, an algorithm is called non-blocking if failure or suspension of any thread cannot cause failure or suspension of another thread; for some operations, these algorithms provide a useful alternative to traditional blocking im ...

. Without CMPXCHG16B one must use workarounds, such as a

critical section In concurrent programming, concurrent accesses to shared resources can lead to unexpected or erroneous behavior, so parts of the program where the shared resource is accessed need to be protected in ways that avoid the concurrent access. One way to ...

or alternative lock-free approaches. Its absence also prevents 64-bit

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

prior to Windows 8.1 from having a

user-mode In computer science, hierarchical protection domains, often called protection rings, are mechanisms to protect data and functionality from faults (by improving fault tolerance) and malicious behavior (by providing computer security). Computer ...

address space larger than 8 TB. The 64-bit version of

Windows 8.1 Windows 8.1 is a release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on August 27, 2013, and broadly released for retail sale on October 17, 2013, about a year after the retail release of its pre ...

requires the instruction. * Early AMD64 and Intel 64 CPUs lacked LAHF and SAHF instructions in 64-bit mode. AMD introduced these instructions (also in 64-bit mode) with their

90 nm The 90 nm process refers to the level of MOSFET (CMOS) fabrication process technology that was commercialized by the 2003–2005 timeframe, by leading semiconductor companies like Toshiba, Sony, Samsung, IBM, Intel, Fujitsu, TSMC, Elpid ...

(revision D) processors, starting with Athlon 64 in October 2004. Intel introduced the instructions in October 2005 with the 0F47h and later revisions of

. The 64-bit version of Windows 8.1 requires this feature. * Early Intel CPUs with Intel 64 also lack the

of the AMD64 architecture. It was added in the stepping E0 (0F41h) in October 2004. This feature is required by all versions of Windows 8. * Early Intel 64 implementations had a 36-bit (64 GB) physical addressing of memory while original AMD64 implementations had a 40-bit (1 TB) physical addressing. Intel used the 40-bit physical addressing first on Xeon MP ( Potomac), launched on 29 March 2005. The difference is not a difference of the user-visible ISAs. In 2007

AMD 10h The AMD Family 10h, or K10, is a microprocessor microarchitecture by AMD based on the K8 microarchitecture. Though there were once reports that the K10 had been canceled,

-based Opteron was the first to provide a 48-bit (256 TB) physical address space. Intel 64's physical addressing was extended to 44 bits (16 TB) in Nehalem-EX in 2010 and to 46 bits (64 TB) in Sandy Bridge E in 2011. With the Ice Lake 3rd gen Xeon Scalable processors, Intel increased the virtual addressing to 57 bits (128 PB) and physical to 52 bits (4 PB) in 2021, necessitating a 5-level paging. The following year AMD64 added the same in 4th generation

EPYC Epyc is a brand of multi-core x86-64 microprocessors designed and sold by AMD, based on the company's Zen microarchitecture. Introduced in June 2017, they are specifically targeted for the server and embedded system markets. Epyc processors share t ...

(Genoa). Non-server CPUs retain smaller address spaces for longer.

Adoption

Processor families in TOP500 supercomputers

supercomputer A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second ( FLOPS) instead of million instructions ...

s tracked by

TOP500 The TOP500 project ranks and details the 500 most powerful non-distributed computing, distributed computer systems in the world. The project was started in 1993 and publishes an updated list of the supercomputers twice a year. The first of these ...

, the appearance of 64-bit extensions for the x86 architecture enabled 64-bit x86 processors by AMD and Intel to replace most RISC processor architectures previously used in such systems (including

and others), as well as 32-bit x86, even though Intel itself initially tried unsuccessfully to replace x86 with a new incompatible 64-bit architecture in the

processor. , a

Fujitsu is a Japanese multinational information and communications technology equipment and services corporation, established in 1935 and headquartered in Tokyo. Fujitsu is the world's sixth-largest IT services provider by annual revenue, and the la ...

A64FX-based supercomputer called Fugaku is number one. The first ARM-based supercomputer appeared on the list in 2018 and, in recent years, non-CPU architecture co-processors (

GPGPU General-purpose computing on graphics processing units (GPGPU, or less often GPGP) is the use of a graphics processing unit (GPU), which typically handles computation only for computer graphics, to perform computation in applications traditiona ...

) have also played a big role in performance. Intel's Xeon Phi "Knights Corner" coprocessors, which implement a subset of x86-64 with some vector extensions, are also used, along with x86-64 processors, in the

Tianhe-2 Tianhe-2 or TH-2 (, i.e. 'Milky Way 2') is a 33.86-petaflops supercomputer located in the National Supercomputer Center in Guangzhou, China. It was developed by a team of 1,300 scientists and engineers. It was the world's fastest supercomputer ac ...

supercomputer.

Operating system compatibility and characteristics

The following operating systems and releases support the x86-64 architecture in

BSD

DragonFly BSD

Preliminary infrastructure work was started in February 2004 for a x86-64 port. This development later stalled. Development started again during July 2007 and continued during

Google Summer of Code The Google Summer of Code, often abbreviated to GSoC, is an international annual program in which Google awards stipends to contributors who successfully complete a free and open-source software coding project during the summer. , the program is ...

2008 and SoC 2009. The first official release to contain x86-64 support was version 2.4.

FreeBSD

FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

first added x86-64 support under the name "amd64" as an experimental architecture in 5.1-RELEASE in June 2003. It was included as a standard distribution architecture as of 5.2-RELEASE in January 2004. Since then, FreeBSD has designated it as a Tier 1 platform. The 6.0-RELEASE version cleaned up some quirks with running x86 executables under amd64, and most drivers work just as they do on the x86 architecture. Work is currently being done to integrate more fully the x86

application binary interface In computer software, an application binary interface (ABI) is an interface between two binary program modules. Often, one of these modules is a library or operating system facility, and the other is a program that is being run by a user. An ' ...

(ABI), in the same manner as the Linux 32-bit ABI compatibility currently works.

NetBSD

x86-64 architecture support was first committed to the

NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is a ...

source tree on June 19, 2001. As of NetBSD 2.0, released on December 9, 2004, ''NetBSD/amd64'' is a fully integrated and supported port. 32-bit code is still supported in 64-bit mode, with a netbsd-32 kernel compatibility layer for 32-bit syscalls. The NX bit is used to provide non-executable stack and heap with per-page granularity (segment granularity being used on 32-bit x86).

OpenBSD

OpenBSD OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD 1.0. According to the website, the OpenBSD project em ...

has supported AMD64 since OpenBSD 3.5, released on May 1, 2004. Complete in-tree implementation of AMD64 support was achieved prior to the hardware's initial release because AMD had loaned several machines for the project's

hackathon A hackathon (also known as a hack day, hackfest, datathon or codefest; a portmanteau of hacking and marathon) is an event where people engage in rapid and collaborative engineering over a relatively short period of time such as 24 or 48 hours. Th ...

that year. OpenBSD developers have taken to the platform because of its support for the

, which allowed for an easy implementation of the

W^X W^X ("write xor execute", pronounced ''W Exclusive or, xor X'') is a computer insecurity, security feature in operating systems and virtual machines. It is a memory (computers), memory protection policy whereby every paging, page in a process (c ...

feature. The code for the AMD64 port of OpenBSD also runs on Intel 64 processors which contains cloned use of the AMD64 extensions, but since Intel left out the page table NX bit in early Intel 64 processors, there is no W^X capability on those Intel CPUs; later Intel 64 processors added the NX bit under the name "XD bit".

Symmetric multiprocessing Symmetric multiprocessing or shared-memory multiprocessing (SMP) involves a multiprocessor computer hardware and software architecture where two or more identical processors are connected to a single, shared main memory, have full access to all ...

(SMP) works on OpenBSD's AMD64 port, starting with release 3.6 on November 1, 2004.

DOS

It is possible to enter

under

DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicatio ...

without a DOS extender, but the user must return to real mode in order to call BIOS or DOS interrupts. It may also be possible to enter

with a

DOS extender A DOS extender is a computer software program running under DOS that enables software to run in a protected mode environment even though the host operating system is only capable of operating in real mode. DOS extenders were initially developed ...

similar to

DOS/4GW DOS/4G is a 32-bit DOS extender developed by Rational Systems (later Tenberry Software). It allows DOS programs to eliminate the 640 KB conventional memory limit by addressing up to 64 MB of extended memory on Intel 80386 and above machines. ...

, but more complex since x86-64 lacks

. DOS itself is not aware of that, and no benefits should be expected unless running DOS in an emulation with an adequate virtualization driver backend, for example: the mass storage interface.

Linux

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

was the first operating system kernel to run the x86-64 architecture in

, starting with the 2.4 version in 2001 (preceding the hardware's availability). Linux also provides backward compatibility for running 32-bit executables. This permits programs to be recompiled into long mode while retaining the use of 32-bit programs. Several Linux distributions currently ship with x86-64-native kernels and userlands. Some, such as

Arch Linux Arch Linux () is an independently developed, x86-64 general-purpose Linux distribution that strives to provide the latest stable versions of most software by following a Rolling release, rolling-release model. The default installation is a minim ...

SUSE SUSE ( , ) is a German-based multinational open-source software company that develops and sells Linux products to business customers. Founded in 1992, it was the first company to market Linux for enterprise. It is the developer of SUSE Linux Ent ...

Mandriva Mandriva S.A. was a public software company specializing in Linux and open-source software. Its corporate headquarters was in Paris, and it had development centers in Metz, France and Curitiba, Brazil. Mandriva, S.A. was the developer and mainta ...

, and

Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of D ...

allow users to install a set of 32-bit components and libraries when installing off a 64-bit DVD, thus allowing most existing 32-bit applications to run alongside the 64-bit OS. Other distributions, such as

Fedora A fedora () is a hat with a soft brim and indented crown.Kilgour, Ruth Edwards (1958). ''A Pageant of Hats Ancient and Modern''. R. M. McBride Company. It is typically creased lengthwise down the crown and "pinched" near the front on both sides ...

Slackware Slackware is a Linux distribution created by Patrick Volkerding in 1993. Originally based on Softlanding Linux System, Slackware has been the basis for many other Linux distributions, most notably the first versions of SUSE Linux distributions ...

and

Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: ''Desktop'', ''Server'', and ''Core'' for Internet of things devices and robots. All the ...

, are available in one version compiled for a 32-bit architecture and another compiled for a 64-bit architecture. Fedora and

Red Hat Enterprise Linux Red Hat Enterprise Linux (RHEL) is a commercial open-source Linux distribution developed by Red Hat for the commercial market. Red Hat Enterprise Linux is released in server versions for x86-64, Power ISA, ARM64, and IBM Z and a desktop version ...

allow concurrent installation of all userland components in both 32 and 64-bit versions on a 64-bit system.

x32 ABI The x32 ABI is an application binary interface (ABI) and one of the interfaces of the Linux kernel. The x32 ABI provides 32-bit integers, long and pointers (ILP32) on Intel and AMD 64-bit hardware. The ABI allows programs to take advantage of the b ...

(Application Binary Interface), introduced in Linux 3.4, allows programs compiled for the x32 ABI to run in the 64-bit mode of x86-64 while only using 32-bit pointers and data fields. Though this limits the program to a virtual address space of 4 GB it also decreases the memory footprint of the program and in some cases can allow it to run faster. 64-bit Linux allows up to 128 TB of virtual address space for individual processes, and can address approximately 64 TB of physical memory, subject to processor and system limitations.

macOS

Mac OS X 10.4.7 and higher versions of

Mac OS X 10.4 Mac OS X Tiger (version 10.4) is the 5th major release of macOS, Apple's desktop and server operating system for Mac computers. Tiger was released to the public on April 29, 2005 for US$129.95 as the successor to Mac OS X 10.3 Panther. Som ...

run 64-bit command-line tools using the POSIX and math libraries on 64-bit Intel-based machines, just as all versions of Mac OS X 10.4 and 10.5 run them on 64-bit PowerPC machines. No other libraries or frameworks work with 64-bit applications in Mac OS X 10.4. The kernel, and all kernel extensions, are 32-bit only.

Mac OS X 10.5 Mac OS X Leopard (version 10.5) is the sixth major release of macOS, Apple's desktop and server operating system for Macintosh computers. Leopard was released on October 26, 2007 as the successor of Mac OS X 10.4 Tiger, and is available in t ...

supports 64-bit GUI applications using

Cocoa Cocoa may refer to: Chocolate * Chocolate * ''Theobroma cacao'', the cocoa tree * Cocoa bean, seed of ''Theobroma cacao'' * Chocolate liquor, or cocoa liquor, pure, liquid chocolate extracted from the cocoa bean, including both cocoa butter and ...

Quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

OpenGL OpenGL (Open Graphics Library) is a cross-language, cross-platform application programming interface (API) for rendering 2D and 3D vector graphics. The API is typically used to interact with a graphics processing unit (GPU), to achieve hardwa ...

, and

X11 The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting wit ...

on 64-bit Intel-based machines, as well as on 64-bit

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., App ...

machines. All non-GUI libraries and frameworks also support 64-bit applications on those platforms. The kernel, and all kernel extensions, are 32-bit only.

Mac OS X 10.6 Mac OS X Snow Leopard (version 10.6) is the seventh major release of macOS, Apple's desktop and server operating system for Macintosh computers. Snow Leopard was publicly unveiled on June 8, 2009 at Apple’s Worldwide Developers Conference. ...

is the first version of

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

that supports a 64-bit

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learnin ...

. However, not all 64-bit computers can run the 64-bit kernel, and not all 64-bit computers that can run the 64-bit kernel will do so by default. The 64-bit kernel, like the 32-bit kernel, supports 32-bit applications; both kernels also support 64-bit applications. 32-bit applications have a virtual address space limit of 4 GB under either kernel. The 64-bit kernel does not support 32-bit kernel extensions, and the 32-bit kernel does not support 64-bit kernel extensions.

OS X 10.8 OS X Mountain Lion (version 10.8) is the ninth major release of macOS, Apple Inc.'s desktop and server operating system for Macintosh computers. OS X Mountain Lion was released on July 25, 2012, for purchase and download through Apple's Mac App ...

includes only the 64-bit kernel, but continues to support 32-bit applications; it does not support 32-bit kernel extensions, however. macOS 10.15 includes only the 64-bit kernel and no longer supports 32-bit applications. This removal of support has presented a problem for

WineHQ Wine (formerly a recursive backronym for ''Wine Is Not an Emulator'', now just "Wine") is a free and open-source compatibility layer that aims to allow application software and computer games developed for Microsoft Windows to run on Unix-like ...

(and the commercial version

CrossOver Crossover may refer to: Entertainment Albums and songs * ''Cross Over'' (Dan Peek album) * ''Crossover'' (Dirty Rotten Imbeciles album), 1987 * ''Crossover'' (Intrigue album) * ''Crossover'' (Hitomi Shimatani album) * ''Crossover'' (Yoshino ...

), as it needs to still be able to run 32-bit Windows applications. The solution, termed ''wine32on64'', was to add

thunk In computer programming, a thunk is a subroutine used to inject a calculation into another subroutine. Thunks are primarily used to delay a calculation until its result is needed, or to insert operations at the beginning or end of the other subro ...

s that bring the CPU in and out of 32-bit compatibility mode in the nominally 64-bit application. macOS uses the

universal binary The universal binary format is, in Apple parlance, a format for executable files that run natively on either PowerPC or Intel-manufactured IA-32 or Intel 64 or ARM64-based Macintosh computers. The format originated on NeXTStep as " Multi-Archi ...

format to package 32- and 64-bit versions of application and library code into a single file; the most appropriate version is automatically selected at load time. In Mac OS X 10.6, the universal binary format is also used for the kernel and for those kernel extensions that support both 32-bit and 64-bit kernels.

Solaris

Solaris Solaris may refer to: Arts and entertainment Literature, television and film * ''Solaris'' (novel), a 1961 science fiction novel by Stanisław Lem ** ''Solaris'' (1968 film), directed by Boris Nirenburg ** ''Solaris'' (1972 film), directed by ...

10 and later releases support the x86-64 architecture. For Solaris 10, just as with the

architecture, there is only one operating system image, which contains a 32-bit kernel and a 64-bit kernel; this is labeled as the "x64/x86" DVD-ROM image. The default behavior is to boot a 64-bit kernel, allowing both 64-bit and existing or new 32-bit executables to be run. A 32-bit kernel can also be manually selected, in which case only 32-bit executables will run. The isainfo command can be used to determine if a system is running a 64-bit kernel. For Solaris 11, only the 64-bit kernel is provided. However, the 64-bit kernel supports both 32- and 64-bit executables, libraries, and system calls.

Windows

x64 editions of Microsoft Windows client and server—

Windows XP Professional x64 Edition Microsoft Windows XP Professional x64 Edition, released on April 25, 2005, is an edition of Windows XP for x86-64 personal computers. It is designed to use the expanded 64-bit memory address space provided by the x86-64 architecture. The prima ...

and

Windows Server 2003 Windows Server 2003 is the sixth version of Windows Server operating system produced by Microsoft. It is part of the Windows NT family of operating systems and was released to manufacturing on March 28, 2003 and generally available on April 24, 2 ...

x64 Edition—were released in March 2005. Internally they are actually the same build (5.2.3790.1830 SP1), as they share the same source base and operating system binaries, so even system updates are released in unified packages, much in the manner as Windows 2000 Professional and Server editions for x86.

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, which was released five years before, at the time being the longest time span between successive releases of ...

, which also has many different editions, was released in January 2007.

Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on July 22, 2009, and became generally available on October 22, 2009. It is the successor to Windows Vista, released nearly ...

was released in July 2009.

Windows Server 2008 R2 Windows Server 2008 R2 is the fifth version of the Windows Server operating system produced by Microsoft and released as part of the Windows NT family of operating systems. It was released to manufacturing on July 22, 2009, and became General av ...

was sold in only x64 and Itanium editions; later versions of Windows Server only offer an x64 edition. Versions of Windows for x64 prior to Windows 8.1 and Windows Server 2012 R2 offer the following: * 8 TB of virtual address space per process, accessible from both user mode and kernel mode, referred to as the user mode address space. An x64 program can use all of this, subject to backing store limits on the system, and provided it is linked with the "large address aware" option, which is present by default. This is a 4096-fold increase over the default 2 GB user-mode virtual address space offered by 32-bit Windows. * 8 TB of kernel mode virtual address space for the operating system. As with the user mode address space, this is a 4096-fold increase over 32-bit Windows versions. The increased space primarily benefits the file system cache and kernel mode "heaps" (non-paged pool and paged pool). Windows only uses a total of 16 TB out of the 256 TB implemented by the processors because early AMD64 processors lacked a CMPXCHG16B instruction. Under Windows 8.1 and Windows Server 2012 R2, both user mode and kernel mode virtual address spaces have been extended to 128 TB. These versions of Windows will not install on processors that lack the CMPXCHG16B instruction. The following additional characteristics apply to all x64 versions of Windows: * Ability to run existing 32-bit applications (.exe programs) and dynamic link libraries (.dlls) using

WoW64 In computing on Microsoft platforms, WoW64 (Windows 32-bit on Windows 64-bit) is a subsystem of the Windows operating system capable of running 32-bit applications on 64-bit Windows. It is included in all 64-bit versions of Windows—including ...

if WoW64 is supported on that version. Furthermore, a 32-bit program, if it was linked with the "large address aware" option, can use up to 4 GB of virtual address space in 64-bit Windows, instead of the default 2 GB (optional 3 GB with /3GB boot option and "large address aware" link option) offered by 32-bit Windows. Unlike the use of the /3GB boot option on x86, this does not reduce the kernel mode virtual address space available to the operating system. 32-bit applications can, therefore, benefit from running on x64 Windows even if they are not recompiled for x86-64. * Both 32- and 64-bit applications, if not linked with "large address aware," are limited to 2 GB of virtual address space. * Ability to use up to 128 GB (Windows XP/Vista), 192 GB (Windows 7), 512 GB (Windows 8), 1 TB (Windows Server 2003), 2 TB (Windows Server 2008/Windows 10), 4 TB (Windows Server 2012), or 24 TB (Windows Server 2016/2019) of physical random access memory (RAM). *

LLP64 In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs are those that are based on processor registers, address buses, or data buses of that size. A compute ...

data model: "int" and "long" types are 32 bits wide, long long is 64 bits, while pointers and types derived from pointers are 64 bits wide. * Kernel mode device drivers must be 64-bit versions; there is no way to run 32-bit kernel mode executables within the 64-bit operating system. User mode device drivers can be either 32-bit or 64-bit. * 16-bit Windows (Win16) and DOS applications will not run on x86-64 versions of Windows due to the removal of the

virtual DOS machine Virtual DOS machines (VDM) refer to a technology that allows running 16-bit/32-bit DOS and 16-bit Windows programs when there is already another operating system running and controlling the hardware. Overview Virtual DOS machines can operate ei ...

subsystem (NTVDM) which relied upon the ability to use virtual 8086 mode. Virtual 8086 mode cannot be entered while running in long mode. * Full implementation of the NX (No Execute) page protection feature. This is also implemented on recent 32-bit versions of Windows when they are started in PAE mode. * Instead of FS segment descriptor on x86 versions of the

family, GS segment descriptor is used to point to two operating system defined structures: Thread Information Block (NT_TIB) in user mode and Processor Control Region (KPCR) in kernel mode. Thus, for example, in user mode GS:0 is the address of the first member of the Thread Information Block. Maintaining this convention made the x86-64 port easier, but required AMD to retain the function of the FS and GS segments in long mode – even though segmented addressing ''per se'' is not really used by any modern operating system. * Early reports claimed that the operating system scheduler would not save and restore the x87 FPU machine state across thread context switches. Observed behavior shows that this is not the case: the x87 state is saved and restored, except for kernel mode-only threads (a limitation that exists in the 32-bit version as well). The most recent documentation available from Microsoft states that the x87/MMX/3DNow! instructions may be used in long mode, but that they are deprecated and may cause compatibility problems in the future. * Some components like

Jet Database Engine The Access Database Engine (also Office Access Connectivity Engine or ACE and formerly Microsoft Jet Database Engine, ''Microsoft JET Engine'' or simply ''Jet'') is a database engine on which several Microsoft products have been built. The firs ...

and

Data Access Objects Jet Data Access Objects is a general programming interface for database access on Microsoft Windows systems, primarily for Jet and ACE databases. History DAO were originally called VT Objects. DAO 1.0 came up in November 1992 as part of Acc ...

will not be ported to 64-bit architectures such as x86-64 and IA-64. *

Microsoft Visual Studio Visual Studio is an integrated development environment (IDE) from Microsoft. It is used to develop computer programs including websites, web apps, web services and mobile apps. Visual Studio uses Microsoft software development platforms such a ...

can compile native applications to target either the x86-64 architecture, which can run only on 64-bit Microsoft Windows, or the

architecture, which can run as a 32-bit application on 32-bit Microsoft Windows or 64-bit Microsoft Windows in

emulation mode. Managed applications can be compiled either in IA-32, x86-64 or AnyCPU modes. Software created in the first two modes behave like their IA-32 or x86-64 native code counterparts respectively; When using the AnyCPU mode, however, applications in 32-bit versions of Microsoft Windows run as 32-bit applications, while they run as a 64-bit application in 64-bit editions of Microsoft Windows.

Video game consoles

Both the

PlayStation 4 The PlayStation 4 (PS4) is a home video game console developed by Sony Interactive Entertainment. Announced as the successor to the PlayStation 3 in February 2013, it was launched on November 15, 2013, in North America, November 29, 2013 in ...

and

Xbox One The Xbox One is a home video game console developed by Microsoft. Announced in May 2013, it is the successor to Xbox 360 and the third base console in the Xbox series of video game consoles. It was first released in North America, parts of ...

, and all variants of those consoles, incorporate AMD x86-64 processors, based on the

Jaguar The jaguar (''Panthera onca'') is a large cat species and the only living member of the genus '' Panthera'' native to the Americas. With a body length of up to and a weight of up to , it is the largest cat species in the Americas and the th ...

. Firmware and games are written in x86-64 code; no legacy x86 code is involved. Their next generations, the

PlayStation 5 The PlayStation 5 (PS5) is a home video game console developed by Sony Interactive Entertainment. Announced as the successor to the PlayStation 4 in April 2019, it was launched on November 12, 2020, in Australia, Japan, New Zealand, North Ame ...

and the

Xbox Series X and Series S The Xbox Series X/S are home video game consoles developed by Microsoft. They were both released on November 10, 2020, as the fourth generation Xbox, succeeding the Xbox One. Along with Sony's PlayStation 5, also released in November 2020, t ...

respectively, also incorporate AMD x86-64 processors, based on the

Zen 2 Zen 2 is a computer processor microarchitecture by AMD. It is the successor of AMD's Zen and Zen+ microarchitectures, and is fabricated on the 7 nanometer MOSFET node from TSMC. The microarchitecture powers the third generation of Ryzen proces ...

microarchitecture. Although considered a PC, the

Steam Deck The Steam Deck is a handheld gaming computer developed by Valve Corporation. Released on February 25, 2022, the Steam Deck can be played as a handheld or connected to a monitor in the same manner as the Nintendo Switch. It is an x86-64-v3 devi ...

uses a custom AMD x86-64

accelerated processing unit AMD Accelerated Processing Unit (APU), formerly known as Fusion, is a series of 64-bit microprocessors from Advanced Micro Devices (AMD), combining a general-purpose AMD64 central processing unit ( CPU) and integrated graphics processing unit ...

(APU), based on the Zen 2 microarchitecture.

Industry naming conventions

Since AMD64 and Intel 64 are substantially similar, many software and hardware products use one vendor-neutral term to indicate their compatibility with both implementations. AMD's original designation for this processor architecture, "x86-64", is still sometimes used for this purpose, as is the variant "x86_64". Other companies, such as

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...

and

Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, the ...

Oracle Corporation Oracle Corporation is an American multinational computer technology corporation headquartered in Austin, Texas. In 2020, Oracle was the third-largest software company in the world by revenue and market capitalization. The company sells da ...

, use the contraction "x64" in marketing material. The term

refers to the

processor, and should not be confused with x86-64, as it is a completely different instruction set. Many operating systems and products, especially those that introduced x86-64 support prior to Intel's entry into the market, use the term "AMD64" or "amd64" to refer to both AMD64 and Intel 64. * amd64 ** Most

BSD The Berkeley Software Distribution or Berkeley Standard Distribution (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berk ...

systems such as

MidnightBSD MidnightBSD is a free Unix, desktop-oriented operating system originally forked from FreeBSD 6.1, and periodically updated with code and drivers from later FreeBSD releases. Its default desktop environment, Xfce, is a lightweight user friendly ...

and

refer to both AMD64 and Intel 64 under the architecture name "amd64". ** Some

Linux distribution A Linux distribution (often abbreviated as distro) is an operating system made from a software collection that includes the Linux kernel and, often, a package management system. Linux users usually obtain their operating system by downloading one ...

s such as

Gentoo Linux Gentoo Linux (pronounced ) is a Linux distribution built using the Portage package management system. Unlike a binary software distribution, the source code is compiled locally according to the user's preferences and is often optimized for the ...

refer to both AMD64 and Intel 64 under the architecture name "amd64". **

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

's x64 versions use the AMD64 moniker internally to designate various components which use or are compatible with this architecture. For example, the

environment variable An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP env ...

PROCESSOR_ARCHITECTURE is assigned the value "AMD64" as opposed to "x86" in 32-bit versions, and the system directory on a Windows x64 Edition installation CD-ROM is named "AMD64", in contrast to "i386" in 32-bit versions. ** Sun's

's ''isalist'' command identifies both AMD64- and Intel 64-based systems as "amd64". **

Java Development Kit The Java Development Kit (JDK) is a distribution of Java Technology by Oracle Corporation. It implements the Java Language Specification (JLS) and the Java Virtual Machine Specification (JVMS) and provides the Standard Edition (SE) of the Java ...

(JDK): the name "amd64" is used in directory names containing x86-64 files. * x86_64 ** The

Linux kernel The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU ope ...

and the

GNU Compiler Collection The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, hardware architectures and operating systems. The Free Software Foundation (FSF) distributes GCC as free software ...

refers to 64-bit architecture as "x86_64". ** Some Linux distributions, such as

openSUSE openSUSE () is a free and open-source software, free and open source RPM Package Manager, RPM-based Linux distribution developed by the openSUSE project. The initial release of the community project was a beta version of SUSE Linux 10.0. Addi ...

refer to this 64-bit architecture as "x86_64". ** Apple

refers to 64-bit architecture as "x86-64" or "x86_64", as seen in the Terminal command arch and in their developer documentation. ** Breaking with most other BSD systems,

DragonFly BSD DragonFly BSD is a free and open-source Unix-like operating system forked from FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and FreeBSD developer between 1994 and 2003, began working on DragonFly BSD in Ju ...

refers to 64-bit architecture as "x86_64". **

Haiku is a type of short form poetry originally from Japan. Traditional Japanese haiku consist of three phrases that contain a ''kireji'', or "cutting word", 17 '' on'' (phonetic units similar to syllables) in a 5, 7, 5 pattern, and a ''kigo'', or se ...

refers to 64-bit architecture as "x86_64".

Licensing

x86-64/AMD64 was solely developed by AMD. AMD holds patents on techniques used in AMD64; those patents must be licensed from AMD in order to implement AMD64. Intel entered into a cross-licensing agreement with AMD, licensing to AMD their patents on existing x86 techniques, and licensing from AMD their patents on techniques used in x86-64. In 2009, AMD and Intel settled several lawsuits and cross-licensing disagreements, extending their cross-licensing agreements.

Notes

References

External links

AMD Developer Guides, Manuals & ISA Documents

– technical talk by the architect of AMD64
video archive
, an
video archive

Intel tweaks EM64T for full AMD64 compatibility

Analyst: Intel Reverse-Engineered AMD64

Early report of differences between Intel IA32e and AMD64

Porting to 64-bit GNU/Linux Systems
by Andreas Jaeger from

GCC Summit The GCC Summit was an annual conference for developers of the GNU Compiler Collection and related free software technologies. The conference was a 3-day event and was held from 2003–2010 in Ottawa, Ontario, Canada with the exception of the 2009 ...

2003. An excellent paper explaining almost all practical aspects for a transition from 32-bit to 64-bit.
Intel 64 Architecture

Intel Software Network: "64 bits"

TurboIRC.COM tutorials, including examples of how to of enter protected and long mode the raw way from DOS

Seven Steps of Migrating a Program to a 64-bit System

Memory Limits for Windows Releases
{{AMD technology Computer-related introductions in 2003 X86 architecture 64-bit computers AMD technologies

AMD64

History

Implementations

Architectural features

Virtual address space details

Canonical form addresses

Page table structure

Operating system limits

Physical address space details

Operating modes

Long mode

Legacy mode

= Protected mode

= Real mode

Intel 64

History

Implementations

VIA's x86-64 implementation

Microarchitecture levels

Differences between AMD64 and Intel 64

Recent implementations

Older implementations

Adoption

Operating system compatibility and characteristics

BSD

DragonFly BSD

FreeBSD

NetBSD

OpenBSD

DOS

Linux

macOS

Solaris

Windows

Video game consoles

Industry naming conventions

Licensing

See also

Notes

References

External links