The Cyrix Cx486 was an

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 ...

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 ...

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 ...

. It primarily competed with the

Intel 486 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 ...

with which it was software compatible, would operate in the same motherboards provided proper support by the

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 ...

was available and generally showed comparable performance. The chip also competed with parts from

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 UMC.

Production

Due to 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 exclus ...

company, Cyrix used

Texas Instruments Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globall ...

, SGS Thomson and IBM which had their own

foundries A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals pr ...

to manufacture their processors, though this was done under a contract that allowed each company to build and sell Cyrix-designed processors under their own branding. As a result, there were many versions of the Cx486 and the manufacture of them differed slightly depending on which company had built them, though equivalent chips generally perform near-identically enough that the end user would not notice any difference between them. The contract with SGS-Thomson outlived the Cyrix Cx486 processor's lifespan in the mainstream market by over a decade with SGS-Thomson still producing industrial solutions built upon the Cyrix design into the late-2000s.

Variants

The Cyrix Cx486 was available with different features, clock speeds and voltages over the duration of its production.

Cx486S

Introduced in May 1993, The Cyrix Cx486S, codenamed M5, was designed to be compatible with the Intel 486SX and like the Intel part, did not have a floating point unit onboard which was of little concern to an average user at the time due to most games and applications using purely

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 ...

-based code. The processor did, however, sport a 2KB Write-back cache and a special "Write-Burst" signal which offered a slight performance boost in certain applications provided the motherboard was capable of utilizing the feature. The processors were labelled "FasCache" to emphasize this feature as most processors used slower Write-through caches. KL Cyrix Cx487S

Users could upgrade the processor to 486DX specifications through use of an accessory, the Cyrix Cx487S which was an

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 ...

Floating Point Unit coprocessor which fit between the CPU and the socket on the motherboard. The table below lists the models of this CPU that were produced. Cyrix Cx486S die

The

Cyrix Cx486DLC The Cyrix Cx486DLC is an x86 desktop microprocessor developed by Cyrix. It was Cyrix's second CPU offering, released years after selling math coprocessors that competed with Intel's units and offered better performance at a comparable or lower ...

is a derivative of this processor and was used to upgrade computers on 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 transistors Despite the faster clock speeds, the 50 MHz version of this processor was less popular than the other models Cyrix had produced. This is likely due to VESA Local Bus being common in computers around the time of the processors introduction as the bus was notoriously unreliable when operating at speeds of over 33 MHz. Many peripherals and even the bus itself will exhibit undefined behaviors at higher speeds on a large number of motherboards. This is reflected by Intel and AMD processors operating at 50 MHz where their sales show a similar trait of being less popular. Users could potentially negate this by increasing latency for the memory, cache and bus but this would also cause performance to drop.

Cx486DX2

Introduced in September 1993 alongside the single clock version was a clock doubling version of the Cx486DX. It was intended to compete with the

Intel 80486DX2 The Intel i486DX2, rumored as 80486DX2 (later renamed IntelDX2) is a CPU produced by Intel that was first introduced in 1992. The i486DX2 was nearly identical to the i486DX, but it had additional clock multiplier circuitry. It was the first chi ...

and had similar capabilities. Its lower price point than equivalent Intel processors made it a popular choice. Cyrix Cx486DX2-V66 die

The 50 MHz version is again the least common, this time likely due to the slower bus speed rendering any upgrade questionable as the performance gains would be reduced by the lower bus speed. The 80 MHz version was introduced in November 1994.

Cx486DX4

The final version of the Cx486 to bear the Cyrix name was a Clock Tripling CPU which was only available with a 100 MHz Internal Clock. Introduced in September 1995, it was otherwise not vastly different to the older designs and proved to be competitive both performance-wise and price-wise against offerings from AMD and Intel though it was later to market than its competitors.

Legal Dispute

In 1993, Intel alleged that Cyrix had infringed several patents and initiated legal action. The courts found that Cyrix had indeed reverse engineered the Intel part, but had conceived their own compatible design, the courts also found that Texas Instruments, SGS-Thomson and IBM were licensed to produce Intel designs. Eventually the case was dropped and Intel paid Cyrix $12 million to drop anti-trust charges against them. The legal battle delayed several of Cyrix's products, causing them to arrive later than competing solutions.

Embedded Solutions

The Cyrix Cx486DX2 design was used by STMicroelectronics in 1999 for their STPC SoC range. This was essentially a Cyrix Cx486, chipset, graphics and most I/O integrated into a single chip. The CPU performs identically to a Cyrix part at the same clock speed. The STPC was produced until 2008 and was found in a variety of systems, usually small embedded systems for industrial use or

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 ...

devices, such as those using the

PC/104 PC/104 (or PC104) is a family of embedded computer standardization, standards which define both Computer form factor, form factors and Bus (computing), computer buses by the PC/104 Consortium. Its name derives from the 104 pins on the interboard ...

form factor. One notable difference between the STPC and other Cx486 processors is the Host Clock which operates at 66 MHz for STPC devices. As such, the 66 MHz model does not use clock doubling at all, but the 133 MHz version does. This differs from most competing systems, such as the

AMD Élan 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 manufactu ...

processors based on AMD's Enhanced

Am486 The Am486 is a 80486-class family of computer processors that was produced by AMD in the 1990s. Intel beat AMD to market by nearly four years, but AMD priced its 40 MHz 486 at or below Intel's price for a 33 MHz chip, offering abo ...

core as used in the

Am5x86 The Am5x86 processor is an x86-compatible CPU announced in November of 1995 by AMD for use in 486-class computer systems. It began shipping in December of 1995, with a base price of $93 per unit in bulk quantities. Before being released, it wa ...

which still relied upon a 33 MHz external clock.http://datasheets.chipdb.org/AMD/Elan/SC5x0/SC520/520tech1.pdf AMD Elan Datasheet

References

{{Reflist Cyrix x86 microprocessors