Intel I860
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The Intel i860 (also known as 80860) is a
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 ...
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
design introduced by
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 ...
in 1989. It is one of Intel's first attempts at an entirely new, high-end
instruction set architecture 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 ' ...
since the failed
Intel 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 imp ...
from the beginning of the 1980s. It was the world's first million-transistor chip. It was released with considerable fanfare, slightly obscuring the earlier
Intel i960 Intel's i960 (or 80960) was a RISC-based microprocessor design that became popular during the early 1990s as an embedded microcontroller. It became a best-selling CPU in that segment, along with the competing AMD 29000. In spite of its success, ...
, which was successful in some niches of
embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' as ...
s, and which many considered to be a better design. The i860 never achieved commercial success and the project was terminated in the mid-1990s.


Implementations

The first implementation of the i860 architecture is the i860 XR microprocessor (code-named N10), which ran at 25, 33, or 40 MHz. The second-generation i860 XP microprocessor (code named N11) added 4 Mbyte pages, larger on-chip caches, second level cache support, faster buses, and hardware support for bus snooping, for cache consistency in
multiprocessor Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There ar ...
systems. A process shrink for the XP (from 1 μm to 0.8
CHMOS CHMOS refers to one of a series of Intel CMOS processes developed from their HMOS process. (H stands for high-density). It was first developed in 1981. CHMOS was used in the Intel 80C51BH, a new version of their standard MCS-51 microcontroller. ...
V) increased the clock to 40 and 50 MHz. Both microprocessors supported the same instruction set for application programs.


Technical features

The i860 combined a number of features that were unique at the time, most notably its
very long instruction word 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 ...
(VLIW) architecture and powerful support for high-speed floating-point operations. The design uses two classes of instructions: "core" instructions which use a
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 ...
ALU, and "floating-point or graphics" instructions which operate on a floating-point adder, a floating-point multiplier, or a 64-bit integer graphics unit. The system had separate pipelines for the ALU, floating-point adder, floating-point multiplier, and graphics unit. It can fetch and decode one "core" instruction and one "floating-point or graphics" instruction per clock. When using dual-operation floating-point instructions (which transfer values between subsequent dual-operation instructions), it is able to execute up to three operations (one ALU, one floating-point multiply, and one floating-point add-or-subtract) per clock. All of the data buses were at least 64 bits wide. The internal memory bus to the cache, for instance, was 128 bits wide. The "core" class instructions use thirty-two 32-bit integer registers. But the "floating-point or graphics" instructions use a register file that can be accessed by the floating point units as either thirty-two 32-bit, sixteen 64-bit, or eight 128-bit floating-point registers, or that can be accessed by the graphics unit as sixteen 64-bit integer registers. The "core" unit is responsible for fetching instructions, and in the normal "single-instruction" mode can fetch one 32-bit "core" or one 32-bit "floating point or graphics" instruction per cycle. But when executing in dual-instruction mode, the instruction cache is accessed as VLIW instructions consisting of a 32-bit "core" instruction paired with a 32-bit "floating-point or graphics" instruction, simultaneously fetched together over a 64-bit bus. Intel referred to the design as the "i860 64-Bit Microprocessor". Intel i860 instructions acted on data sizes from 8-bit through 128-bit. The graphics unit was unique for the era. It supported a number of commands for
SIMD Single instruction, multiple data (SIMD) is a type of parallel processing in Flynn's taxonomy. SIMD can be internal (part of the hardware design) and it can be directly accessible through an instruction set architecture (ISA), but it should ...
-like instructions in addition to basic 64-bit integer math. For instance, its 64-bit integer datapath can represent multiple pixels together as either 8-bit pixels, 16-bit pixels, or 32-bit pixels. Experience with the i860 influenced the MMX functionality later added to Intel's
Pentium Pentium is a brand used for a series of x86 architecture-compatible microprocessors produced by Intel. The original Pentium processor from which the brand took its name was first released on March 22, 1993. After that, the Pentium II and Pe ...
processors. One unusual feature of the i860 was that the pipelines into the functional units were program-accessible (
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 ...
), requiring the
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 ...
s to order instructions carefully in the
object code In computing, object code or object module is the product of a compiler. In a general sense object code is a sequence of statements or instructions in a computer language, usually a machine code language (i.e., binary) or an intermediate langua ...
to keep the pipelines filled. In traditional architectures these duties were handled at runtime by a scheduler on the CPU itself, but the complexity of these systems limited their application in early RISC designs. The i860 was an attempt to avoid this entirely by moving this duty off-chip into the compiler. This allowed the i860 to devote more room to functional units, improving performance. As a result of its architecture, the i860 could run certain graphics and floating-point algorithms with exceptionally high speed, but its performance in general-purpose applications suffered and it was difficult to program efficiently (see below).


Performance

On paper, performance was impressive for a single-chip solution; however, real-world performance was anything but. One problem, perhaps unrecognized at the time, was that runtime code paths are difficult to predict, meaning that it becomes exceedingly difficult to order instructions properly at
compile time In computer science, compile time (or compile-time) describes the time window during which a computer program is compiled. The term is used as an adjective to describe concepts related to the context of program compilation, as opposed to concept ...
. For instance, an instruction to add two numbers will take considerably longer if those numbers are not in the cache, yet there is no way for the programmer to know if they are or not. If an incorrect guess is made, the entire pipeline will stall, waiting for the data. The entire i860 design was based on the compiler efficiently handling this task, which proved almost impossible in practice. While theoretically capable of peaking at about 60-80 MFLOPS for both
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- ...
and
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 ...
for the XP versions, manually written assembler code managed to get only about up to 40 MFLOPS, and most compilers had difficulty getting even 10 MFLOPs. The later
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, also a VLIW design, suffered again from the problem of compilers incapable of delivering sufficiently optimized code. Another serious problem was the lack of any solution to handle
context switch In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point, and then restoring a different, previously saved, state. This allows multiple processes ...
ing quickly. The i860 had several pipelines (for the ALU and FPU parts) and an interrupt could spill them and require them all to be re-loaded. This took 62 cycles in the best case, and almost 2000 cycles in the worst. The latter is 1/20000th of a second at 40 MHz (50 microseconds), an eternity for a CPU. This largely eliminated the i860 as a general purpose CPU.


Demise

As the compilers improved, the general performance of the i860 did likewise, but by then most other RISC designs had already passed the i860 in performance. In the late 1990s, Intel replaced their entire RISC line with
ARM In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...
-based designs, known as the
XScale XScale is a microarchitecture for central processing units initially designed by Intel implementing the ARM architecture (version 5) instruction set. XScale comprises several distinct families: IXP, IXC, IOP, PXA and CE (see more below), with some ...
. Confusingly, the 860 number has since been re-used for a motherboard control chipset for Intel
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 ...
(high-end
Pentium Pentium is a brand used for a series of x86 architecture-compatible microprocessors produced by Intel. The original Pentium processor from which the brand took its name was first released on March 22, 1993. After that, the Pentium II and Pe ...
) systems and a model of the Core i7.
Andy Grove Andrew Stephen Grove (born András István Gróf; 2 September 193621 March 2016) was a Hungarian-American businessman and engineer who served as the third CEO of Intel Corporation. He escaped from Communist-controlled Hungary at the age of 20 ...
suggested that the i860's failure in the marketplace was due to Intel being stretched too thin:


Applications

At first, the i860 was only used in a small number of
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 such as the Intel iPSC/860. Intel later marketed the i860 as a workstation microprocessor for a time, where it competed with microprocessors based on the MIPS 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 ...
architectures, among others. The
Oki Electric , commonly referred to as OKI, OKI Electric or the OKI Group, is a Japanese information and communications technology company, headquartered in Toranomon, Minato-ku, Tokyo and operating in over 120 countries around the world. OKI produced the fi ...
OKI Station 7300/30 and
Stardent Stardent Computer, Inc. was a manufacturer of graphics supercomputer workstations in the late 1980s. The company was formed in 1989 when Ardent Computer Corporation (formerly Dana Computer, Inc.) and Stellar Computer Inc. merged. History Stellar ...
Vistra 800
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
workstations were based on a 40 MHz i860 XR running
UNIX System V Unix System V (pronounced: "System Five") is one of the first commercial versions of the Unix operating system. It was originally developed by AT&T and first released in 1983. Four major versions of System V were released, numbered 1, 2, 3, an ...
/i860. The
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4860 and
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CP486 featured an
Intel 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 ...
and i860 on the same motherboard. Microsoft initially developed what was to become
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 ...
on internally designed i860XR-based workstations (codenamed ''Dazzle''), only porting NT to the MIPS ( Microsoft Jazz),
Intel 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 transistors The i860 did see some use in the
workstation A workstation is a special computer designed for technical or scientific applications. Intended primarily to be used by a single user, they are commonly connected to a local area network and run multi-user operating systems. The term ''workstat ...
world as a graphics accelerator. It was used, for instance, in the
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, where it ran a cut-down version of the
Mach kernel Mach () is a kernel developed at Carnegie Mellon University by Richard Rashid and Avie Tevanian to support operating system research, primarily distributed and parallel computing. Mach is often considered one of the earliest examples of a microk ...
running a complete
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stack. However, the
PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, Doug Br ...
part of the project was never finished so it ended up just moving color pixels around. In this role, the i860 design worked considerably better, as the core program could be loaded into the cache and made entirely "predictable", allowing the compilers to get the ordering right.
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produced an i860-based accelerator board intended for use with their Targa and Vista framebuffer cards.
Pixar Pixar Animation Studios (commonly known as Pixar () and stylized as P I X A R) is an American computer animation studio known for its critically and commercially successful computer animated feature films. It is based in Emeryville, Californi ...
produced a custom version of
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to run on the card that ran approximately four times faster than the 386 host. Another example was
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's
RealityEngine RealityEngine is a 3D graphics hardware architecture and a family of graphics systems which was developed and manufactured by Silicon Graphics during the early to mid 1990s. RealityEngine was positioned as the company's high-end visualization har ...
, which used a number of i860XP processors in its geometry engine. This sort of use slowly disappeared as well, as more general-purpose CPUs started to match the i860's performance, and as Intel turned its focus to
Pentium Pentium is a brand used for a series of x86 architecture-compatible microprocessors produced by Intel. The original Pentium processor from which the brand took its name was first released on March 22, 1993. After that, the Pentium II and Pe ...
processors for general-purpose computing.
Mercury Computer Systems Mercury Systems, Inc. is a technology company serving the aerospace and defense industry. It designs, develops and manufactures open architecture computer hardware and software products, including secure embedded processing modules and subsystem ...
used the i860 in their
multicomputer Parallel computing is a type of computation in which many calculations or processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be solved at the same time. There are several different fo ...
. From 2 to 360 compute nodes would reside in a
circuit switched Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full b ...
fat tree The fat tree network is a universal network for provably efficient communication. It was invented by Charles E. Leiserson of the Massachusetts Institute of Technology in 1985. k-ary n-trees, the type of fat-trees commonly used in most high-perf ...
network, with each node having local memory that could be mapped by any other node. Each node in this heterogeneous system could be an i860, a
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 ...
, or a group of three SHARC DSPs. Good performance was obtained from the i860 by supplying customers with a library of signal processing functions written in assembly language. The hardware packed up to 360 compute nodes in 9U of
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space, making it suitable for mobile applications such as airborne radar processing. During the early 1990s, Stratus Technologies built i860-based servers, the XA/R series, running their proprietary VOS operating system. Also in the 1990s,
Alliant Computer Systems Alliant Computer Systems Corporation was a computer company that designed and manufactured parallel computing systems. Together with Pyramid Technology and Sequent Computer Systems, Alliant's machines pioneered the symmetric multiprocessing market ...
built their i860-based FX/800 and FX/2800 servers, replacing the FX/80 and FX/8 series that had been based on the Motorola 68000 ISA. Both the Alliant and Mercury compute systems were in heavy use at NASA/JPL for the SIR-C missions. The U.S. military used the i860 for numerous aerospace and
digital signal processing Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...
applications as a coprocessor, where it saw use up until the late 1990s.


References

*


External links


Many i860 expansion cards

i860 images and description
* Rhodehamel, Michael W.
The Bus Interface and Paging Units of the i860(tm) Microprocessor
. In Proc. IEEE International Conference on Computer Design, p. 380–384, 1989. {{Authority control Graphics chips Intel graphics I860 Very long instruction word computing 32-bit microprocessors