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The Cyrix 5x86 was a line of x86
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 circ ...
s designed 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. In ...
and released on June 5 of 1995. Cyrix, being a fabless company, had the chips manufactured by IBM. The line came out about 5 months before the more famous Cyrix 6x86. The
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 ...
5x86 was one of the fastest
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, a ...
s ever produced for Socket 3
computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...
systems. With better performance in most applications than an
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 ser ...
Pentium processor at 75  MHz, the Cyrix Cx5x86 filled a gap by providing a medium-performance processor option for
486 __NOTOC__ Year 486 (Roman numerals, CDLXXXVI) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Basilius and Longinus (or, less freq ...
Socket 3 motherboards (which are incapable of handling Intel's Pentium CPUs, apart from the
Pentium Overdrive The Pentium OverDrive was a microprocessor marketing brand name used by Intel, to cover a variety of consumer upgrade products sold in the mid-1990s. It was originally released for 486 motherboards, and later some Pentium sockets. Intel dropped the ...
). The IBM 5x86C is an IBM branded and produced version of the
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 ...
-designed Cyrix Cx5x86
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, a ...
. Previous IBM x86 processors, IBM 386SLC and
IBM 486SLC The 386SLC was an Intel-licensed version of the 386SX (32-bit internal, 16-bit external, 24-bit memory addressing), developed and manufactured by IBM in 1991. It included power-management capabilities and an 8KB internal CPU cache, which enabled i ...
, were based on modified Intel designs.


Design

The Cyrix 5x86 processor, codename "M1sc", was based on a scaled-down version of the "M1" core used in the Cyrix 6x86, which provided 80% of the performance for a 50% decrease in
transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...
s over the 6x86 design. It had the
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 calculati ...
memory bus of an ordinary 486 processor, but internally had much more in common with fifth-generation processors such as the Cyrix 6x86, the AMD K5, and the Intel Pentium, and even the sixth-generation Intel Pentium Pro. The chip featured near-complete support for i486 instructions, but very limited support for Pentium instructions. Some performance-enhancing features of the CPU were intentionally disabled due to potentially stability-threatening bugs which were not fixed before release time (these features can be enabled with freely downloadable software utilities; see below). The similarly named SGS-Thomson (STMicroelectronics) ST5x86 and IBM 5x86C were licensed rebrandings of the Cyrix design (IBM and ST physically produced Cyrix's CPUs for them), marketed separately but identical for practical purposes, apart from the availability of a 75 MHz edition which Cyrix did not bring to market, and slight differences in voltage requirements. The Cyrix 5x86 design, however, should not be confused with the similarly named
AMD 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 was essentially a clock-quadrupled 486 (not an all-new design like the Cyrix part) but which had broadly similar performance, used the same Socket 3, and was introduced at the end of the same year. Cyrix's 5x86 was a very short-lived chip, having a market life of only six months. It is likely Cyrix could have continued to successfully sell processors based on Socket 3, but canned the 5x86 so that it would not compete with its then new 6x86 offerings.


Controversies and anomalies

The official Cyrix 5x86 website boasted about several features of the chip that were disabled by default in the final versions. The most controversial of these features was the "branch-prediction" feature, which was enabled in the benchmarks results on the company website when comparing the chip to Intel's Pentium processor. While it was possible to enable the extra features using a special software utility, it usually resulted in an unstable system, especially on earlier steppings of the chip when running 32-bit code. There are also many rumours surrounding a 133 MHz, clock-quadrupled version of the Cyrix 5x86. The 133 MHz version is very rare, however, and producers of upgrade kits were given preferential access to it, notably Gainbery. Some of the 100 and 120 MHz parts also contain support for the 4X multiplier setting, and some of these chips may also work at 133 MHz. However, the 5x86 is not known to overclock well; 120 MHz is generally considered to be pushing the limitations of the process on which it was fabricated. An 80 MHz (2×40 MHz) 5x86 also exists, but is unclear as to whether or not it was ever officially released. IBM's 5x86C was considered to be more conservatively rated than the Cyrix branded parts, and operated at a lower voltage (3.3V). For example: what Cyrix would rate as a 100 MHz part, IBM would mark as 75 MHz. IBM 5x86C was available as 75 MHz and 100 MHz parts. A few examples of 120 MHz parts also exist, but they have early production dates indicating that they may have been produced prior to IBM's decision to scale back clock speeds. 5x86C also had a much longer production run than the Cyrix branded parts. IBM continued to produce 5x86C at least until late 1998 ( QFP only), whereas Cyrix's own part was discontinued in 1996. Parts which implement the 4X multiplier or Stepping 1 Rev 3 cores are not known to exist.


Specifications

* iDX4WB pinout, 168 pins * Socket 3 * 2.0 million transistors on 0.65 micrometre process * 144mm² die * 3.45 volts * 16
kilobyte The kilobyte is a multiple of the unit byte for digital information. The International System of Units (SI) defines the prefix '' kilo'' as 1000 (103); per this definition, one kilobyte is 1000 bytes.International Standard IEC 80000-13 Quant ...
s unified level-one cache
100 MHz
capable edition for 33 MHz (33×3), and 50 MHz (50×2) front side bus100 MHz
capable edition for 33 MHz (33×3), and 25 MHz (25×4) front side bus120/133 MHz
capable edition for 40 MHz (40×3) and 33 MHz (33×4) front side bus.


References


External links

{{commons category
Comparative performance benchmarks
* ttps://web.archive.org/web/20031020013939/http://homepage3.nifty.com/sandy55/PowerBoard/PowerBoard.html Information on write-back cache performance-enhancing utility from Evergreen Techsee "Cyrix5x86" section in the middle of the page and "et9603.exe" hyperlink) Cx586 586