The 8086 (also called iAPX 86) is a

16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...

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 (allowing the use of cheaper and fewer supporting ICs),Fewer TTL buffers, latches, multiplexers (although the amount of TTL logic was not drastically reduced). It also permits the use of cheap 8080-family ICs, where the 8254 CTC, 8255 PIO, and 8259 PIC were used in the IBM PC design. In addition, it makes PCB layout simpler and boards cheaper, as well as demanding fewer (1- or 4-bit wide) DRAM chips. and is notable as the processor used in the original

IBM PC The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...

design. The 8086 gave rise to the x86 architecture, which eventually became Intel's most successful line of processors. On June 5, 2018, Intel released a limited-edition CPU celebrating the 40th anniversary of the Intel 8086, called the Intel Core i7-8086K.

History

Background

In 1972, Intel launched the 8008, the first 8-bit microprocessor.using enhancement load PMOS logic (requiring 14 V, achieving TTL compatibility by having V_CC at +5 V and V_DD at −9 V). It implemented an

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 ' ...

designed by Datapoint Corporation with programmable CRT terminals in mind, which also proved to be fairly general-purpose. The device needed several additional ICs to produce a functional computer, in part due to it being packaged in a small 18-pin "memory package", which ruled out the use of a separate address bus (Intel was primarily a

DRAM Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-oxid ...

manufacturer at the time). Two years later, Intel launched the 8080,Using non-saturated enhancement-load NMOS logic (demanding a higher gate voltage for the load-transistor gates). employing the new 40-pin DIL packages originally developed for

calculator An electronic calculator is typically a portable electronic device used to perform calculations, ranging from basic arithmetic to complex mathematics. The first solid-state electronic calculator was created in the early 1960s. Pocket-sized ...

ICs to enable a separate address bus. It has an extended instruction set that is

source-compatible Source-code compatibility (source-compatible) means that a program can run on computers (or operating systems), independently of binary-code compatibility and that the source code is needed for portability. The source code must be compiled befor ...

(not binary compatible) with the 8008 and also includes some

instructions to make programming easier. The 8080 device was eventually replaced by the depletion-load-based

8085 The Intel 8085 ("''eighty-eighty-five''") is an 8-bit microprocessor produced by Intel and introduced in March 1976. It is software-binary compatible with the more-famous Intel 8080 with only two minor instructions added to support its added i ...

(1977), which sufficed with a single +5 V power supply instead of the three different operating voltages of earlier chips.Made possible with depletion-load nMOS logic (the 8085 was later made using HMOS processing, just like the 8086). Other well known 8-bit microprocessors that emerged during these years are Motorola 6800 (1974), General Instrument PIC16X (1975), MOS Technology 6502 (1975), Zilog Z80 (1976), and Motorola 6809 (1978).

The first x86 design

The 8086 project started in May 1976 and was originally intended as a temporary substitute for the ambitious and delayed

iAPX 432 The iAPX 432 (''Intel Advanced Performance Architecture'') is a discontinued computer architecture introduced in 1981. It was Intel's first 32-bit processor design. The main processor of the architecture, the ''general data processor'', is impl ...

project. It was an attempt to draw attention from the less-delayed 16-bit and

32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32-bit units. Compared to smaller bit widths, 32-bit computers can perform large calculation ...

processors of other manufacturers — Motorola,

Zilog Zilog, Inc. is an American manufacturer of microprocessors and 8-bit and 16-bit microcontrollers. It is also a supplier of application-specific embedded system-on-chip (SoC) products. Its most famous product is the Z80 series of 8-bit microp ...

, and National Semiconductor. Whereas the 8086 was a 16-bit microprocessor, it used the same

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 ...

as Intel's 8-bit microprocessors (8008, 8080, and 8085). This allowed

assembly language In computer programming, assembly language (or assembler language, or symbolic machine code), often referred to simply as Assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence be ...

programs written in 8-bit to seamlessly migrate. New instructions and features — such as signed integers, base+offset addressing, and self-repeating operations — were added. Instructions were added to assist source code compilation of nested functions in the ALGOL-family of languages, including

Pascal Pascal, Pascal's or PASCAL may refer to: People and fictional characters * Pascal (given name), including a list of people with the name * Pascal (surname), including a list of people and fictional characters with the name ** Blaise Pascal, Fren ...

and PL/M. According to principal architect

Stephen P. Morse Stephen Paul Morse (born May 1940) is the architect of the Intel 8086 chip and is the originator of the "One Step" search page tools used by genealogists. Early life Morse was born in Brooklyn, New York. He has degrees in electrical engineerin ...

, this was a result of a more software-centric approach. Other enhancements included

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 ...

instructions for the multiply and divide assembly language instructions. Designers also anticipated coprocessors, such as 8087 and

8089 The Intel 8089 input/output coprocessor was available for use with the 8086/8088 central processor. It was announced in May 1979, but the price was not available at that time. It used the same programming technique as 8087 for input/output operat ...

, so the bus structure was designed to be flexible. The first revision of the instruction set and high level architecture was ready after about three months,Rev.0 of the instruction set and architecture was ready in about three months, according to Morse. and as almost no CAD tools were used, four engineers and 12 layout people were simultaneously working on the chip.Using rubylith, light boards, rulers, electric erasers, and a

digitizer DigitizationTech Target. (2011, April). Definition: digitization. ''WhatIs.com''. Retrieved December 15, 2021, from https://whatis.techtarget.com/definition/digitization is the process of converting information into a digital (i.e. computer-r ...

(according to Jenny Hernandez, member of the 8086 design team, in a statement made on Intel's webpage for its 25th birthday). The 8086 took a little more than two years from idea to working product, which was considered rather fast for a complex design in 1976–1978. The 8086 was sequenced8086 used less microcode than many competitors' designs, such as the MC68000 and others using a mixture of

random logic Random logic is a semiconductor circuit design technique that translates high-level logic descriptions directly into hardware features such as AND and OR gates. The name derives from the fact that few easily discernible patterns are evident in the a ...

and

and was implemented using depletion-load nMOS circuitry with approximately 20,000 active transistors (29,000 counting all ROM and

PLA PLA may refer to: Organizations Politics and military * People's Liberation Army, the armed forces of China and of the ruling Chinese Communist Party * People's Liberation Army (disambiguation) ** Irish National Liberation Army, formerly called ...

sites). It was soon moved to a new refined nMOS manufacturing process called HMOS (for High performance MOS) that Intel originally developed for manufacturing of fast

static RAM Static random-access memory (static RAM or SRAM) is a type of random-access memory (RAM) that uses latching circuitry (flip-flop) to store each bit. SRAM is volatile memory; data is lost when power is removed. The term ''static'' differen ...

products.Fast static RAMs in MOS technology (as fast as bipolar RAMs) was an important product for Intel during this period. This was followed by HMOS-II, HMOS-III versions, and, eventually, a fully static

CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...

version for battery powered devices, manufactured using Intel's CHMOS processes.CHMOS is Intel's name for CMOS circuits manufactured using processing steps very similar to HMOS. The original chip measured 33 mm² and minimum feature size was 3.2 μm. The architecture was defined by

with some help from Bruce Ravenel (the architect of the 8087) in refining the final revisions. Logic designer Jim McKevitt and John Bayliss were the lead engineers of the hardware-level development teamOther members of the design team were Peter A.Stoll and Jenny Hernandez. and Bill Pohlman the manager for the project. The legacy of the 8086 is enduring in the basic instruction set of today's personal computers and servers; the 8086 also lent its last two digits to later extended versions of the design, such as the Intel 286 and the Intel 386, all of which eventually became known as the x86 family. (Another reference is that the PCI Vendor ID for Intel devices is 8086_h.)

Details

Buses and operation

All internal registers, as well as internal and external data buses, are 16 bits wide, which firmly established the "16-bit microprocessor" identity of the 8086. A 20-bit external address bus provides a 1 MB physical address space (2²⁰ = 1,048,576 x 1 byte). This address space is addressed by means of internal memory "segmentation". The data bus is multiplexed with the address bus in order to fit all of the control lines into a standard 40-pin

dual in-line package In microelectronics, a dual in-line package (DIP or DIL), is an electronic component package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board (P ...

. It provides a 16-bit I/O address bus, supporting 64 KB of separate I/O space. The maximum linear address space is limited to 64 KB, simply because internal address/index registers are only 16 bits wide. Programming over 64 KB memory boundaries involves adjusting the segment registers (see below); this difficulty existed until the

80386 The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistors80286 did not help in this regard, as its registers are still only 16 bits wide).

Hardware modes of 8086

Some of the control pins, which carry essential signals for all external operations, have more than one function depending upon whether the device is operated in ''min'' or ''max'' mode. The former mode is intended for small single-processor systems, while the latter is for medium or large systems using more than one processor (a kind of multiprocessor mode). Maximum mode is required when using an 8087 or 8089 coprocessor. The voltage on pin 33 (MN/) determines the mode. Changing the state of pin 33 changes the function of certain other pins, most of which have to do with how the CPU handles the (local) bus.The IBM PC and PC/XT use an Intel 8088 running in maximum mode, which allows the CPU to work with an optional 8087 coprocessor installed in the math coprocessor socket on the PC or PC/XT mainboard. (The PC and PC/XT may require maximum mode for other reasons, such as perhaps to support the DMA controller.) The mode is usually hardwired into the circuit and therefore cannot be changed by software. The workings of these modes are described in terms of timing diagrams in Intel datasheets and manuals. In minimum mode, all control signals are generated by the 8086 itself.

Registers and instruction

The 8086 has eight more or less general 16-bit registers (including the stack pointer but excluding the instruction pointer, flag register and segment registers). Four of them, AX, BX, CX, DX, can also be accessed as twice as many 8-bit registers (see figure) while the other four, SI, DI, BP, SP, are 16-bit only. Due to a compact encoding inspired by 8-bit processors, most instructions are one-address or two-address operations, which means that the result is stored in one of the operands. At most one of the operands can be in memory, but this memory operand can also be the ''destination'', while the other operand, the ''source'', can be either ''register'' or ''immediate''. A single memory location can also often be used as both ''source'' and ''destination'' which, among other factors, further contributes to a

code density 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 ' ...

comparable to (and often better than) most eight-bit machines at the time. The degree of generality of most registers is much greater than in the 8080 or 8085. However, 8086 registers were more specialized than in most contemporary

minicomputer A minicomputer, or colloquially mini, is a class of smaller general purpose computers that developed in the mid-1960s and sold at a much lower price than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, ...

s and are also used implicitly by some instructions. While perfectly sensible for the assembly programmer, this makes register allocation for compilers more complicated compared to more orthogonal 16-bit and 32-bit processors of the time such as the

PDP-11 The PDP-11 is a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of all models were sold, ...

, VAX, 68000,

32016 The NS32000, sometimes known as the 32k, is a series of microprocessors produced by National Semiconductor. The first member of the family came to market in 1982, briefly known as the 16032 before becoming the 32016. It was the first 32-bit general ...

, etc. On the other hand, being more regular than the rather minimalistic but ubiquitous 8-bit microprocessors such as the 6502, 6800,

6809 The Motorola 6809 ("''sixty-eight-oh-nine''") is an 8-bit microprocessor with some 16-bit features. It was designed by Motorola's Terry Ritter and Joel Boney and introduced in 1978. Although source compatible with the earlier Motorola 6800, the ...

MCS-48 The MCS-48 microcontroller series, Intel's first microcontroller, was originally released in 1976. Its first members were 8048, 8035 and 8748. The 8048 is probably the most prominent member of the family. Initially, this family was produced us ...

8051 The Intel MCS-51 (commonly termed 8051) is a single chip microcontroller (MCU) series developed by Intel in 1980 for use in embedded systems. The architect of the Intel MCS-51 instruction set was John H. Wharton. Intel's original versions were po ...

, and other contemporary accumulator-based machines, it is significantly easier to construct an efficient code generator for the 8086 architecture. Another factor for this is that the 8086 also introduced some new instructions (not present in the 8080 and 8085) to better support stack-based high-level programming languages such as Pascal and PL/M; some of the more useful instructions are push ''mem-op'', and ret ''size'', supporting the "Pascal calling convention" directly. (Several others, such as push ''immed'' and enter, were added in the subsequent 80186, 80286, and 80386 processors.) A 64 KB (one segment)

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 ...

growing towards lower addresses is supported in hardware; 16-bit words are pushed onto the stack, and the top of the stack is pointed to by SS:SP. There are 256 interrupts, which can be invoked by both hardware and software. The interrupts can cascade, using the stack to store the return addresses. The 8086 has 64 K of 8-bit (or alternatively 32 K of 16-bit word) I/O port space.

Flags

The 8086 has a 16-bit flags register. Nine of these condition code flags are active, and indicate the current state of the processor: Carry flag (CF), Parity flag (PF), Auxiliary carry flag (AF), Zero flag (ZF), Sign flag (SF), Trap flag (TF), Interrupt flag (IF),

Direction flag The direction flag is a flag that controls the ''left-to-right'' or ''right-to-left'' direction of string processing, stored in the FLAGS register on all x86-compatible CPUs.Overflow flag (OF). Also referred to as the status word, the layout of the flags register is as follows:

Segmentation

There are also four 16-bit segment registers (see figure) that allow the 8086

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

to access one

megabyte The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix ''mega'' is a multiplier of (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes o ...

of memory in an unusual way. Rather than concatenating the segment register with the address register, as in most processors whose address space exceeds their register size, the 8086 shifts the 16-bit segment only four bits left before adding it to the 16-bit offset (16×segment + offset), therefore producing a 20-bit external (or effective or physical) address from the 32-bit segment:offset pair. As a result, each external address can be referred to by 2¹² = 4096 different segment:offset pairs. Although considered complicated and cumbersome by many programmers, this scheme also has advantages; a small program (less than 64 KB) can be loaded starting at a fixed offset (such as 0000) in its own segment, avoiding the need for relocation, with at most 15 bytes of alignment waste. Compilers for the 8086 family commonly support two types of pointer, ''near'' and ''far''. Near pointers are 16-bit offsets implicitly associated with the program's code or data segment and so can be used only within parts of a program small enough to fit in one segment. Far pointers are 32-bit segment:offset pairs resolving to 20-bit external addresses. Some compilers also support ''huge'' pointers, which are like far pointers except that pointer arithmetic on a huge pointer treats it as a linear 20-bit pointer, while pointer arithmetic on a far pointer wraps around within its 16-bit offset without touching the segment part of the address. To avoid the need to specify ''near'' and ''far'' on numerous pointers, data structures, and functions, compilers also support "memory models" which specify default pointer sizes. The ''tiny'' (max 64K), ''small'' (max 128K), ''compact'' (data > 64K), ''medium'' (code > 64K), ''large'' (code,data > 64K), and ''huge'' (individual arrays > 64K) models cover practical combinations of near, far, and huge pointers for code and data. The ''tiny'' model means that code and data are shared in a single segment, just as in most 8-bit based processors, and can be used to build ''

.com The domain name .com is a top-level domain (TLD) in the Domain Name System (DNS) of the Internet. Added at the beginning of 1985, its name is derived from the word ''commercial'', indicating its original intended purpose for domains registere ...

'' files for instance. Precompiled libraries often come in several versions compiled for different memory models. According to Morse et al.,. the designers actually contemplated using an 8-bit shift (instead of 4-bit), in order to create a 16 MB physical address space. However, as this would have forced segments to begin on 256-byte boundaries, and 1 MB was considered very large for a microprocessor around 1976, the idea was dismissed. Also, there were not enough pins available on a low cost 40-pin package for the additional four address bus pins. In principle, the address space of the x86 series ''could'' have been extended in later processors by increasing the shift value, as long as applications obtained their segments from the operating system and did not make assumptions about the equivalence of different segment:offset pairs.Some 80186 clones did change the shift value, but were never commonly used in desktop computers. In practice the use of "huge" pointers and similar mechanisms was widespread and the flat 32-bit addressing made possible with the 32-bit offset registers in the 80386 eventually extended the limited addressing range in a more general way. The instruction stream is fetched from memory as words and is addressed internally by the processor to the byte level as necessary. An instruction stream queuing mechanism allows up to 6 bytes of the instruction stream to be queued while waiting for decoding and execution. The queue acts as a First-In-First-Out (FIFO) buffer, from which the Execution Unit (EU) extracts instruction bytes as required. Whenever there is space for at least two bytes in the queue, the BIU will attempt a word fetch memory cycle. If the queue is empty (following a branch instruction, for example), the first byte into the queue immediately becomes available to the EU.

Porting older software

Small programs could ignore the segmentation and just use plain 16-bit addressing. This allows

8-bit In computer architecture, 8-bit Integer (computer science), integers or other Data (computing), data units are those that are 8 bits wide (1 octet (computing), octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) arc ...

software to be quite easily ported to the 8086. The authors of most DOS implementations took advantage of this by providing an

Application Programming Interface An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how t ...

very similar to

CP/M CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/ 85-based microcomputers by Gary Kildall of Digital Research, Inc. Initial ...

as well as including the simple ''.com'' executable file format, identical to CP/M. This was important when the 8086 and MS-DOS were new, because it allowed many existing CP/M (and other) applications to be quickly made available, greatly easing acceptance of the new platform.

Example code

The following 8086/8088 assembler source code is for a subroutine named _memcpy that copies a block of data bytes of a given size from one location to another. The data block is copied one byte at a time, and the data movement and looping logic utilizes 16-bit operations. The code above uses the BP (base pointer) register to establish a

call frame In computer science, a call stack is a stack data structure that stores information about the active subroutines of a computer program. This kind of stack is also known as an execution stack, program stack, control stack, run-time stack, or mach ...

, an area on the stack that contains all of the parameters and local variables for the execution of the subroutine. This kind of calling convention supports

reentrant Reentrant or re-entrant can refer to: *Re-entrant (landform), the low ground formed between two hill spurs. *Reentrancy (computing) in computer programming *Reentrant mutex in computer science *Reentry (neural circuitry) in neuroscience *Salients ...

and recursive code, and has been used by most ALGOL-like languages since the late 1950s. The above routine is a rather cumbersome way to copy blocks of data. The 8086 provides dedicated instructions for copying strings of bytes. These instructions assume that the source data is stored at DS:SI, the destination data is stored at ES:DI, and that the number of elements to copy is stored in CX. The above routine requires the source and the destination block to be in the same segment, therefore DS is copied to ES. The loop section of the above can be replaced by: This copies the block of data one byte at a time. The REP instruction causes the following MOVSB to repeat until CX is zero, automatically incrementing SI and DI and decrementing CX as it repeats. Alternatively the MOVSW instruction can be used to copy 16-bit words (double bytes) at a time (in which case CX counts the number of words copied instead of the number of bytes). Most assemblers will properly recognize the REP instruction if used as an in-line prefix to the MOVSB instruction, as in REP MOVSB. This routine will operate correctly if interrupted, because the program counter will continue to point to the REP instruction until the block copy is completed. The copy will therefore continue from where it left off when the interrupt service routine returns control.

Performance

Although partly shadowed by other design choices in this particular chip, the multiplexed address and data buses limit performance slightly; transfers of 16-bit or 8-bit quantities are done in a four-clock memory access cycle, which is faster on 16-bit, although slower on 8-bit quantities, compared to many contemporary 8-bit based CPUs. As instructions vary from one to six bytes, fetch and execution are made concurrent and decoupled into separate units (as it remains in today's x86 processors): The ''bus interface unit'' feeds the instruction stream to the ''execution unit'' through a 6-byte prefetch queue (a form of loosely coupled pipelining), speeding up operations on registers and immediates, while memory operations became slower (four years later, this performance problem was fixed with the 80186 and 80286). However, the full (instead of partial) 16-bit architecture with a full width

ALU ALU, Alu or alu may refer to: Computing and science ;Computing *Arithmetic logic unit, a digital electronic circuit ;Biology * Alu sequence, a type of short stretch of DNA *'' Arthrobacter luteus'', a bacterium Organizations * Abraham Lincoln ...

meant that 16-bit arithmetic instructions could now be performed with a single ALU cycle (instead of two, via internal carry, as in the 8080 and 8085), speeding up such instructions considerably. Combined with orthogonalizations of operations versus operand types and addressing modes, as well as other enhancements, this made the performance gain over the 8080 or 8085 fairly significant, despite cases where the older chips may be faster (see below). * EA = time to compute effective address, ranging from 5 to 12 cycles. * Timings are best case, depending on prefetch status, instruction alignment, and other factors. As can be seen from these tables, operations on registers and immediates were fast (between 2 and 4 cycles), while memory-operand instructions and jumps were quite slow; jumps took more cycles than on the simple 8080 and

, and the 8088 (used in the IBM PC) was additionally hampered by its narrower bus. The reasons why most memory related instructions were slow were threefold: * Loosely coupled fetch and execution units are efficient for instruction prefetch, but not for jumps and random data access (without special measures). * No dedicated address calculation adder was afforded; the microcode routines had to use the main ALU for this (although there was a dedicated ''segment'' + ''offset'' adder). * The address and data buses were multiplexed, forcing a slightly longer (33~50%) bus cycle than in typical contemporary 8-bit processors. However, memory access performance was drastically enhanced with Intel's next generation of 8086 family CPUs. The 80186 and 80286 both had dedicated address calculation hardware, saving many cycles, and the 80286 also had separate (non-multiplexed) address and data buses.

Floating point

The 8086/8088 could be connected to a mathematical coprocessor to add hardware/microcode-based

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. The

Intel 8087 The Intel 8087, announced in 1980, was the first x87 floating-point coprocessor for the 8086 line of microprocessors. The purpose of the 8087 was to speed up computations for floating-point arithmetic, such as addition, subtraction, multiplicati ...

was the standard math coprocessor for the 8086 and 8088, operating on 80-bit numbers. Manufacturers like

Cyrix Cyrix Corporation was a microprocessor developer that was founded in 1988 in Richardson, Texas, as a specialist supplier of floating point units for 286 and 386 microprocessors. The company was founded by Tom Brightman and Jerry Rogers. In 19 ...

(8087-compatible) and Weitek (''not'' 8087-compatible) eventually came up with high-performance floating-point coprocessors that competed with the 8087.

Chip versions

The clock frequency was originally limited to 5 MHz,(IBM PC used 4.77 MHz, 4/3 the standard NTSC color burst frequency) but the last versions in HMOS were specified for 10 MHz. HMOS-III and

versions were manufactured for a long time (at least a while into the 1990s) for embedded systems, although its successor, the 80186/

80188 The Intel 80188 microprocessor was a variant of the Intel 80186. The 80188 had an 8-bit external data bus instead of the 16-bit bus of the 80186; this made it less expensive to connect to peripherals. The 16-bit registers and the one megabyte add ...

(which includes some on-chip peripherals), has been more popular for embedded use. The 80C86, the CMOS version of the 8086, was used in the

GRiDPad GRiDPad was a trademarked name for a series of pen computing tablets built by Grid Systems Corporation. The GRiDPad 1900, released in 1989, is regarded as the first commercially successful tablet computer. Jeff Hawkins went on to use the GRiD ...

Toshiba T1200 The Toshiba T1200 is a discontinued laptop that was manufactured by the Toshiba Corporation, first made in 1987. It is an upgraded version of the Toshiba T1100 Plus. It is equipped with an Intel 80C86 processor at of which 384 KB can be used for ...

, HP 110, and finally the 1998–1999

Lunar Prospector ''Lunar Prospector'' was the third mission selected by NASA for full development and construction as part of the Discovery Program. At a cost of $62.8 million, the 19-month mission was designed for a low polar orbit investigation of the Moon, ...

. For the packaging, the Intel 8086 was available both in ceramic and plastic DIP packages.

List of Intel 8086

Derivatives and clones

Compatible—and, in many cases, enhanced—versions were manufactured by

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 ...

, Harris/ Intersil, OKI,

Siemens Siemens AG ( ) is a German multinational conglomerate corporation and the largest industrial manufacturing company in Europe headquartered in Munich with branch offices abroad. The principal divisions of the corporation are ''Industry'', '' ...

, Texas Instruments, NEC,

Mitsubishi The is a group of autonomous Japanese multinational companies in a variety of industries. Founded by Yatarō Iwasaki in 1870, the Mitsubishi Group historically descended from the Mitsubishi zaibatsu, a unified company which existed from 1870 ...

, and AMD. For example, the NEC V20 and NEC V30 pair were hardware-compatible with the 8088 and 8086 even though NEC made original Intel clones μPD8088D and μPD8086D respectively, but incorporated the instruction set of the 80186 along with some (but not all) of the 80186 speed enhancements, providing a drop-in capability to upgrade both instruction set and processing speed without manufacturers having to modify their designs. Such relatively simple and low-power 8086-compatible processors in CMOS are still used in embedded systems. The electronics industry of the Soviet Union was able to replicate the 8086 through . The resulting chip, K1810VM86, was binary and pin-compatible with the 8086. i8086 and i8088 were respectively the cores of the Soviet-made PC-compatible EC1831 and EC1832 desktops. (EC1831 is the EC identification of IZOT 1036C and EC1832 is the EC identification of IZOT 1037C, developed and manufactured in Bulgaria. EC stands for Единая Система.) However, the EC1831 computer (IZOT 1036C) had significant hardware differences from the IBM PC prototype. The EC1831 was the first PC-compatible computer with dynamic bus sizing (US Pat. No 4,831,514). Later some of the EC1831 principles were adopted in PS/2 (US Pat. No 5,548,786) and some other machines (UK Patent Application, Publication No. GB-A-2211325, Published June 28, 1989).

Support chips

* Intel 8237: direct memory access (DMA) controller * Intel 8251: universal synchronous/asynchronous receiver/transmitter at 19.2 kbit/s * Intel 8253: programmable interval timer, 3x 16-bit max 10 MHz * Intel 8255: programmable peripheral interface, 3x 8-bit I/O pins used for printer connection etc. * Intel 8259: programmable interrupt controller *

Intel 8279 The Intel 8279 is a keyboard and display controller developed for interfacing to Intel 8085 The Intel 8085 ("''eighty-eighty-five''") is an 8-bit microprocessor produced by Intel and introduced in March 1976. It is software-binary compatible w ...

: keyboard/display controller, scans a keyboard matrix and display matrix like 7-seg * Intel 8282/ 8283: 8-bit latch * Intel 8284: clock generator * Intel 8286/ 8287: bidirectional 8-bit driver. In 1980 both Intel I8286/I8287 (industrial grade) version were available for US$16.25 in quantities of 100. * Intel 8288: bus controller * Intel 8289: bus arbiter * NEC µPD765 or Intel 8272A: floppy controller

Microcomputers using the 8086

* The Intel Multibus-compatible

single-board computer A single-board computer (SBC) is a complete computer built on a single circuit board, with microprocessor(s), memory, input/output (I/O) and other features required of a functional computer. Single-board computers are commonly made as demonstrati ...

ISBC 86/12 was announced in 1978. * The

Xerox NoteTaker The Xerox NoteTaker is a portable computer developed at Xerox PARC in Palo Alto, California, in 1978. Although it did not enter production, and only around ten prototypes were built, it strongly influenced the design of the later Osborne 1 and Com ...

was one of the earliest portable computer designs in 1978 and used three 8086 chips (as CPU, graphics processor, and I/O processor), but never entered commercial production. *

Seattle Computer Products Seattle Computer Products (SCP) was a Tukwila, Washington, microcomputer hardware company which was one of the first manufacturers of computer systems based on the 16-bit Intel 8086 processor. SCP began shipping its first S-100 bus 8086 CPU bo ...

shipped S-100 bus based 8086 systems (SCP200B) as early as November 1979. * The Norwegian Mycron 2000, introduced in 1980. * One of the most influential microcomputers of all, the

, used the Intel 8088, a version of the 8086 with an 8-bit data bus (as mentioned above). * The first Compaq Deskpro used an 8086 running at 7.16 MHz, but was compatible with add-in cards designed for the 4.77 MHz

IBM PC XT The IBM Personal Computer XT (model 5160, often shortened to PC/XT) is the second computer in the IBM Personal Computer line, released on March 8, 1983. Except for the addition of a built-in hard drive and extra expansion slots, it is very simila ...

and could switch the CPU down to the lower speed (which also switched in a memory bus buffer to simulate the 8088's slower access) to avoid software timing issues. * An 8 MHz 8086-2 was used in the AT&T 6300 PC (built by Olivetti, and known globally under several brands and model numbers), an IBM PC-compatible desktop microcomputer. The M24 / PC 6300 has IBM PC/XT compatible 8-bit expansion slots, but some of them have a proprietary extension providing the full 16-bit data bus of the 8086 CPU (similar in concept to the 16-bit slots of the IBM PC AT, but different in the design details, and physically incompatible), and all system peripherals including the onboard video system also enjoy 16-bit data transfers. The later Olivetti M24SP featured an 8086-2 running at the full maximum 10 MHz. * The IBM PS/2 models 25 and 30 were built with an 8 MHz 8086. * The Amstrad PC1512, PC1640, PC2086, PC3086 and PC5086 all used 8086 CPUs at 8 MHz. * The NEC PC-9801. * The Tandy 1000 SL-series and RL machines used 9.47 MHz 8086 CPUs. * The

IBM Displaywriter The IBM 6580 Displaywriter System is a 16-bit microcomputer that was marketed and sold by IBM's Office Products Division primarily as a word processor. Announced in June 1980 and effectively withdrawn from marketing in July 1986, the system was s ...

word processing machine and the Wang Professional Computer, manufactured by Wang Laboratories, also used the 8086. * NASA used original 8086 CPUs on equipment for ground-based maintenance of the Space Shuttle Discovery until the end of the space shuttle program in 2011. This decision was made to prevent software regression that might result from upgrading or from switching to imperfect clones. * KAMAN Process and Area Radiation MonitorsKaman Tech. Manual

Notes

References

External links

Intel datasheets

List of 8086 CPUs and their clones at CPUworld.com

Maximum Mode InterfaceArchived
from the original on July 21, 2011. Retrieved July 10, 2022.

(

PDF Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...

document)
8086 program codes using emu8086 (Version 4.08) Emulator
* * ** ** ** ** ** ** ** {{Authority control Computer-related introductions in 1978 80086 16-bit microprocessors