The Cyrix 6x86 is a line of sixth-generation,

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 a maximum of 32- bit units. Compared to smaller bit widths, 32-bit computers can perform la ...

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 8086 microprocessor and its 8-bit-external-bus variant, the 8088. Th ...

microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...

s designed and released by

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. Ter ...

in 1995. Cyrix, being a

fabless Fabless manufacturing is the design and sale of hardware devices and semiconductor chips while outsourcing their fabrication (or ''fab'') to a specialized manufacturer called a semiconductor foundry. These foundries are typically, but not exclu ...

company, had the chips manufactured by

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

and

SGS-Thomson STMicroelectronics NV (commonly referred to as ST or STMicro) is a European multinational semiconductor contract manufacturing and design company. It is the largest of such companies in Europe. It was founded in 1987 from the merger of two st ...

. The 6x86 was made as a direct competitor to Intel's

Pentium Pentium is a series of x86 architecture-compatible microprocessors produced by Intel from 1993 to 2023. The Pentium (original), original Pentium was Intel's fifth generation processor, succeeding the i486; Pentium was Intel's flagship proce ...

microprocessor line, and was pin compatible. During the 6x86's development, the majority of applications ( office software as well as games) performed almost entirely

integer An integer is the number zero (0), a positive natural number (1, 2, 3, ...), or the negation of a positive natural number (−1, −2, −3, ...). The negations or additive inverses of the positive natural numbers are referred to as negative in ...

operations. The designers foresaw that future applications would most likely maintain this instruction focus. So, to optimize the chip's performance for what they believed to be the most likely application of the CPU, the integer execution resources received most of the transistor budget. This would later prove to be a strategic mistake, as the popularity of the P5 Pentium caused many

software developer Software development is the process of designing and Implementation, implementing a software solution to Computer user satisfaction, satisfy a User (computing), user. The process is more encompassing than Computer programming, programming, wri ...

s to hand-optimize code in

assembly language In computing, assembly language (alternatively 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 bet ...

, to take advantage of the P5 Pentium's tightly pipelined and lower latency FPU. For example, the highly anticipated

first-person shooter A first-person shooter (FPS) is a video game genre, video game centered on gun fighting and other weapon-based combat seen from a First person (video games), first-person perspective, with the player experiencing the action directly through t ...

'' Quake'' used highly optimized assembly code designed almost entirely around the P5 Pentium's FPU. As a result, the P5 Pentium significantly outperformed other CPUs in the game. After Cyrix was bought by

National Semiconductor National Semiconductor Corporation was an United States of America, American Semiconductor manufacturing, semiconductor manufacturer, which specialized in analogue electronics, analog devices and subsystems, formerly headquartered in Santa Clara, ...

then later VIA, the 6x86 continued to be produced up until the early 2000s.

History

The 6x86, previously under the codename "M1" was announced by Cyrix in October 1995. On release only the 100 MHz (P120+) version was available, but a 120 MHz (P150+) version was planned for mid-1995 with a 133 MHz (P166+) model later. The 100 MHz (P120+) 6x86 was available to OEMs for a price of $450 per chip in bulk quantities. In mid February 1996 Cyrix announced the P166+, P150+, and P133+ to be added to the 6x86 model line. IBM, who produced the chips, also announced they will be selling their own versions of the chips. The 6x86 P200+ was planned for the end of 1996, and ended up being released in June. The M2 (6x86MX) was first announced to be in development in mid 1996. It would have MMX and 32-bit optimization. The M2 would also have some of the same features as the Intel Pentium Pro such as register renaming, out-of-order completion, and speculative execution. Additionally it would have 64 KB of cache over the original 6x86 and Pentium Pro's 16 KB. In March 1997 when asked about when the M2 line of processors would begin shipping, Cyrix UK managing director Brendan Sherry stated, "I've read it's going to be May but we've said late Q2 all along and I'm pretty sure we'll make that." The 6x86L was first released in January 1997 to address the heat issues with the original 6x86 line. The 6x86L had a lower V-core voltage and required a split power plane

voltage regulator A voltage regulator is a system designed to automatically maintain a constant voltage. It may use a simple feed-forward design or may include negative feedback. It may use an electromechanical mechanism or electronic components. Depending on the ...

. In April 1997 the first laptop to use the 6x86 processor was put on sale. They were sold by TigerDirect and had a 12.1in DSTN display, 16 MB of memory, 10x CD-ROM, 1.3 GB hard disk drive, and cost $1,899 for the base price. Later by the end of May 1997 on the 27th, Cyrix said they would announce details of the new chip line (6x86MX) the day before Computex in June 1997. For the low end of the series, the PR166 6x86MX was available for $190 with higher end PR200 and PR233 versions available for $240 and $320. IBM being the producer of Cyrix's chips, would also sell their own version. Cyrix hoped to ship tens of thousands within June 1997 with up to 1 million by the end of the year. Cyrix also expected to release a 266 MHz chip by the end of 1997 and a 300 MHz in the first quarter of 1998. They had slightly better

floating point In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a signed sequence of a fixed number of digits in some base) multiplied by an integer power of that base. Numbers of this form ...

performance, which cut adding and multiply times by a third, but it was still slower than the Intel Pentium. The M2 also had full MMX instructions, 64 KB of cache over the original 16 KB, and had a lower core voltage of 2.5V over 3.3V of the original 6x86 line. National Semiconductor acquired Cyrix in July 1997. National Semiconductor was not interested in high performance processors but rather

system on a chip A system on a chip (SoC) is an integrated circuit that combines most or all key components of a computer or Electronics, electronic system onto a single microchip. Typically, an SoC includes a central processing unit (CPU) with computer memory, ...

devices, and wanted to shift the focus of Cyrix to the

MediaGX The MediaGX CPU is an x86-compatible processor that was designed by Cyrix and manufactured by National Semiconductor following the two companies' merger. It was introduced in 1997. The core is based on the integration of the Cyrix Cx5x86 CPU co ...

line. In January 1998 National Semiconductors produced a 6x86MX processor on a 0.25

micron The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

process technology. This reduced the chip size from 150 square millimeters to 88. National shifted their production of the MII and MediaGX to 0.25 by August. In September 1998 IBM's licensing partnership with Cyrix was said to be ended by National Semiconductors. This was due to National wanting to increase production of Cyrix chips in their own facilities, and because having IBM produce Cyrix's chips was causing issues such as profit losses due to IBM frequently pricing their versions of Cyrix's chips lower. National would be paying $50–55 million to IBM to end the partnership, which would end the following April. National would then be moving chip production to their own facility in South Portland,

Maine Maine ( ) is a U.S. state, state in the New England region of the United States, and the northeasternmost state in the Contiguous United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Provinces and ...

. The Cyrix MII was released in May 1998. These chips were not exciting like people had hoped, as they were just a rebranding of the 6x86MX. In December these chips cost $80 for a MII-333, $59 for a MII-300, $55 for a MII-266, and $48 for a MII-233. In May 1999 National Semiconductor decided to leave the PC chip market due to significant losses, and put the Cyrix CPU division up for sale. VIA bought the Cyrix line in June 1999, and ended the development of high performance processors. The MII-433GP would be the last processor produced by Cyrix. Additionally after VIA's acquisition, the 6x86/L was discontinued, but the 6x86MX/MII line continued to be sold by VIA. VIA would continue to produce the MII throughout the early 2000s. It was expected to be discontinued when the VIA Cyrix MII was released. However, the MII was still available for sale until mid/late 2003, being shown on VIA's website as a product until October, and it still saw use in devices such as network computers.

Architecture

The 6x86 is

superscalar A superscalar processor (or multiple-issue processor) is a CPU that implements a form of parallelism called instruction-level parallelism within a single processor. In contrast to a scalar processor, which can execute at most one single in ...

and

superpipelined In computer engineering, instruction pipelining is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing incoming in ...

and performs

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

speculative execution Speculative execution is an optimization (computer science), optimization technique where a computer system performs some task that may not be needed. Work is done before it is known whether it is actually needed, so as to prevent a delay that woul ...

out-of-order execution In computer engineering, out-of-order execution (or more formally dynamic execution) is an instruction scheduling paradigm used in high-performance central processing units to make use of instruction cycles that would otherwise be wasted. In t ...

, and

data dependency A data dependency in computer science is a situation in which a program statement (instruction) refers to the data of a preceding statement. In compiler theory, the technique used to discover data dependencies among statements (or instructions) i ...

removal. However, it continued to use native

execution and ordinary

microcode In processor design, microcode serves as an intermediary layer situated between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. It consists of a set of hardware-level instructions ...

only, like

Centaur A centaur ( ; ; ), occasionally hippocentaur, also called Ixionidae (), is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse that was said to live in the mountains of Thessaly. In one version o ...

Winchip The WinChip series is a discontinued CPU electrical consumption, low-power Socket 7-based x86 central processing unit, processor that was designed by Centaur Technology and marketed by its parent company Integrated Device Technology, IDT. Overvie ...

, unlike competitors

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and Delaware General Corporation Law, incorporated in Delaware. Intel designs, manufactures, and sells computer compo ...

and

AMD Advanced Micro Devices, Inc. (AMD) is an American multinational corporation and technology company headquartered in Santa Clara, California and maintains significant operations in Austin, Texas. AMD is a hardware and fabless company that de ...

which introduced the method of dynamic translation to

micro-operation In computer central processing units, micro-operations (also known as micro-ops or μops, historically also as micro-actions) are detailed low-level instructions used in some designs to implement complex machine instructions (sometimes termed ma ...

s with

Pentium Pro The Pentium Pro is a sixth-generation x86 microprocessor developed and manufactured by Intel and introduced on November 1, 1995. It implements the P6 (microarchitecture), P6 microarchitecture (sometimes termed i686), and was the first x86 Intel C ...

and K5. The 6x86 is

socket Socket may refer to: Mechanics * Socket wrench, a type of wrench that uses separate, removable sockets to fit different sizes of nuts and bolts * Socket head screw, a screw (or bolt) with a cylindrical head containing a socket into which the hexag ...

-compatible with the Intel P54C

, and was offered in six performance levels: PR 90+, PR 120+, PR 133+, PR 150+, PR 166+ and PR 200+. These performance levels do not map to the clock speed of the chip itself (for example, a PR 133+ ran at 110 MHz, a PR 166+ ran at 133 MHz, etc.). With regard to internal caches, it has a 16- KB primary cache and a fully associative 256-byte instruction line cache is included alongside the primary cache, which functions as the primary instruction cache. The 6x86 and 6x86L were not completely compatible with the Intel P5

instruction set In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, s ...

and are not multi-processor capable. For this reason, the chip identified itself as an 80486 and disabled the CPUID instruction by default. CPUID support could be enabled by first enabling extended CCR registers then setting bit 7 in CCR4. The lack of full P5 Pentium compatibility caused problems with some applications because programmers had begun to use P5 Pentium-specific instructions. Some companies released patches for their products to make them function on the 6x86. Compatibility with the Pentium was improved in the 6x86MX, by adding a Time Stamp Counter to support the P5 Pentium's RDTSC instruction. Support for the Pentium Pro's CMOVcc instructions were also added.

Performance

Similarly to

with their K5 and early K6 processors, Cyrix used a PR rating (Performance Rating) to relate their performance to the Intel P5

(pre- P55C), as the 6x86's higher per-clock performance relative to a P5 Pentium could be quantified against a higher-clocked Pentium part. For example, a 133 MHz 6x86 will match or outperform a P5 Pentium at 166 MHz, and as a result Cyrix could market the 133 MHz chip as being a P5 Pentium 166's equal. However, the PR rating was not an entirely truthful representation of the 6x86's performance. While the 6x86's integer performance was significantly higher than P5 Pentium's, its floating point performance was more mediocre—between 2 and 4 times the performance of the 486 FPU per clock cycle (depending on the operation and precision). The FPU in the 6x86 was largely the same circuitry that was developed for Cyrix's earlier high performance

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

/ 80287/ 80387-compatible coprocessors, which was very fast for its time—the Cyrix FPU was much faster than the 80387, and even the 80486 FPU. However, it was still considerably slower than the new and completely redesigned P5 Pentium and P6

Pentium III The Pentium III (marketed as Intel Pentium III Processor, informally PIII or P3) brand refers to Intel's 32-bit x86 desktop and mobile CPUs based on the sixth-generation P6 (microarchitecture), P6 microarchitecture introduced on February 28, 1999 ...

FPUs. One of the main features of the P5/P6 FPUs is that they supported interleaving of FPU and integer instructions in their design, which Cyrix chips did not integrate. This caused very poor performance with Cyrix CPUs on games and software that took advantage of this. Therefore, despite being very fast clock by clock, the 6x86 and MII were forced to compete at the low-end of the market as AMD K6 and Intel P6

Pentium II The Pentium II is a brand of sixth-generation Intel x86 microprocessors based on the P6 (microarchitecture), P6 microarchitecture, introduced on May 7, 1997. It combined the ''P6'' microarchitecture seen on the Pentium Pro with the MMX (instruc ...

were always ahead on clock speed. The 6x86's and MII's old generation "486 class" floating point unit combined with an integer section that was at best on-par with the newer P6 and K6 chips meant that Cyrix could no longer compete in performance.

Models and variants

6x86

The ''6x86'' (codename M1) was released by

in 1996. The first generation of 6x86 had heat problems. This was primarily caused by their higher heat output than other x86 CPUs of the day and, as such, computer builders sometimes did not equip them with adequate cooling. The CPUs topped out at around 25 W heat output (like the

AMD K6 The K6 microprocessor was launched by AMD in 1997. The main advantage of this particular microprocessor is that it was designed to fit into existing desktop designs for Pentium-branded CPUs. It was marketed as a product that could perform as wel ...

), whereas the P5 Pentium produced around 15 W of

waste heat Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...

at its peak. However, both numbers would be a fraction of the heat generated by many high performance processors, some years later. Shortly after the original M1, the M1R was released. The M1R was a switch from SGS-Thomson 3M process to IBM 5M process, making the 6x86 chips 50% smaller. Image:Cyrix_6x86_early_die.jpg, Early Cyrix 6x86 (M1) die shot

6x86L

The 6x86L (codename M1L) was later released by

to address heat issues; the ''L'' standing for ''low-power''. Improved manufacturing technologies permitted usage of a lower Vcore. Just like the Pentium MMX, the 6x86L required a split power plane voltage regulator with separate voltages for I/O and CPU core. Image:Cyrix_6x86_die.JPG, Cyrix 6x86L (M1L) die shot

6x86MX / MII

Another release of the 6x86, the 6x86MX, added MMX compatibility along with the EMMI instruction set, improved compatibility with the Pentium and Pentium Pro by adding a Time Stamp Counter and CMOVcc instructions respectively, and quadrupled the primary cache size to 64 KB. The 256-byte instruction line cache can be turned into a scratchpad cache to provide support for multimedia operations. Later revisions of this chip were renamed MII, to better compete with the Pentium II processor. 6x86MX / MII was late to market, and couldn't scale well in clock speed with the manufacturing processes used at the time. File:Cyrix 6x86MX die.JPG, Cyrix 6x86MX (M2) die shot

Model table

Timeline

References

External links

*
Cyrix 6x86 ("M1")
at PCGuide
cpu-collection.de
Cyrix 6x86 processor images and descriptions

in-depth analysis of 6th generation x86 CPUs, including the 6x86MX.

at Sandpile.org

Cyrix Datasheets

6x86 (M1/M1R) Guide

6x86 (M1/M1R) Technical Brief

6x86 (MX) Guide

6x86 (MX) Technical Brief

6x86 (MII) Technical Brief
{{Cyrix

686 __NOTOC__ Year 686 (Roman numerals, DCLXXXVI) was a common year starting on Monday of the Julian calendar. The denomination 686 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent ...