Cyrix Cx486#Cx486DX2
{{Short description|486-compatible microprocessor by Cyrix}}
{{Infobox CPU
|name = Cyrix Cx486
|image = Cyrix Cx486DX4.jpg
|image_size = 200px
|caption = A Cyrix Cx486DX4 microprocessor rated for 100MHz operation
|manuf1 = Cyrix
|produced-start = May 1993
|produced-end =
|model =
|transistors =
|slowest = 25 |slow-unit = MHz
|fastest = 100 |fast-unit = MHz
|fsb-slowest = 25 |fsb-slow-unit = MHz
|fsb-fastest = 33 |fsb-fast-unit = MHz
|soldby =
|sock1 =
|sock2 =
|brand1 =
|microarch =
|cpuid =
|code =
|numcores = 1
|l1cache = 2 KB (S)
8 KB (DX/DX2/DX4)
|application = Desktop
|predecessor = Cyrix Cx486SLC, Cyrix Cx486DLC
|successor = Cyrix 5x86, Cyrix 6x86
}}
{{for|similarly named Cyrix chips competing with the Intel 386|Cyrix Cx486SLC|Cyrix Cx486DLC}}
The Cyrix Cx486 was an x86 microprocessor designed by Cyrix. It primarily competed with the Intel 486 with which it was software compatible, would operate in the same motherboards provided proper support by the BIOS was available and generally showed comparable performance.{{cite web |url=http://www.cpu-collection.de/?tn=0&l0=co&l1=Cyrix&l2=Cx486%20DX |title=Cx486 DX |website=CPU-Collection.de}} The chip also competed with parts from AMD and UMC.
Production
File:Cyrix 486 DX4 100 Front.jpgDue to Cyrix being a fabless company, Cyrix used Texas Instruments, SGS Thomson and IBM which had their own foundries 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.{{cite news |url=https://www.latimes.com/archives/la-xpm-1992-05-14-fi-3052-story.html |newspaper=Los Angeles Times |title=Texas Instruments to Sell Its Own 486 Chip |author=Jonathan Weber |date=May 14, 1992}}
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.{{cite web |url=http://www.ucs.co.uk/pdf/tigerstar.pdf |title=Tiger Star System User's Manual}} - a system using the STPC SoC
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 M6, 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-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.{{cite web |url=http://www.cpu-collection.de/?tn=0&l0=co&l1=Cyrix&l2=Cx486+S |title=Cx486 S}} - page with most Cx486S models and their specs
Users could upgrade the processor to 486DX specifications through use of an accessory, the Cyrix Cx487S which was an x87 Floating Point Unit coprocessor which fit between the CPU and the socket on the motherboard.{{cite web |url=http://www.cpu-collection.de/?tn=0&l0=co&l1=Cyrix&l2=FPU#Cx487S-33QP |title=FPU}} - page with Cx487S
The table below lists the models of this CPU that were produced.
| border="1" class="wikitable"
|+ Models of Cx486S ! Model/Feature ! Bus Speed ! Clock Frequency ! Cache ! Voltage ! Notes |
| Cx486S-25
| 25 MHz || 25 MHz || 2KB || 5 Volts DC || Does not have a heatsink. |
|---|
| Cx486S-33
| 33 MHz || 33 MHz || 2KB || 5 Volts DC || Available with permanently attached heatsink. |
| Cx486S-40
| 40 MHz || 40 MHz || 2KB || 5 Volts DC || Available with permanently attached heatsink. |
The Cyrix Cx486DLC is a derivative of this processor and was used to upgrade computers on the 80386 platform.
=Cx486DX=
Codenamed M7, the Cyrix Cx486DX is essentially the same as the Cx486S except it featured an internal Floating Point Unit and quadruple the amount of cache memory. It was available in a form that allowed lower voltage operation. The processor was found to have comparable performance to competing solutions, but it varied depending on the application.
The table below lists models of this CPU that were produced.
| border="1" class="wikitable"
|+ Models of Cx486DX ! Model/Feature ! Bus Speed ! Clock Frequency ! Cache ! Voltage ! Notes |
| Cx486DX-33
| 33 MHz || 33 MHz || 8KB || 5 Volts DC || Does not have a heatsink. |
|---|
| Cx486DX-33QP
| 33 MHz || 33 MHz || 8KB || 3.3 Volts DC || QFP Package, Low Voltage. Does not have a heatsink. |
| Cx486DX-40
| 40 MHz || 40 MHz || 8KB || 5 Volts DC || Available with permanently attached heatsink. |
| Cx486DX-50
| 50 MHz || 50 MHz || 8KB || 5 Volts DC || Available with permanently attached heatsink. Uncommon. |
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.{{cite web |url=http://www.pcguide.com/ref/video/ifVLB-c.html |title=VESA Local Bus |website=The PC Guide |quote=VLB has however had its own share of problems. In particular, VLB video cards may cause reliability problems in motherboards running at 40 or 50 MHz. |archive-url=https://web.archive.org/web/20190207203740/http://www.pcguide.com/ref/video/ifVLB-c.html |archive-date=2019-02-07 |url-status=dead}} 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.{{citation needed|date=December 2015}}
=Cx486DX2=
File:Cyrix 486 dx2 66mhz 2007 03 27.jpg
Introduced in September 1993 alongside the single clock version was a clock doubling version of the Cx486DX.{{cite web |url=http://cpu-museum.de/?m=Cyrix&f=Cx486#cpu0460 |title=Cx486 |archive-url=https://web.archive.org/web/20161024170848/http://cpu-museum.de/?m=Cyrix&f=Cx486#cpu0460 |archive-date=2016-10-24 |url-status=deviated}} - page with most models of Cx486DX2 It was intended to compete with the Intel 80486DX2 and had similar capabilities. Its lower price point than equivalent Intel processors made it a popular choice.{{cite web |url=https://www.pctechguide.com/cyrix-cpus |title=Cyrix CPUs}} - page talking about Cyrix processors in general
File:Cyrix Cx486DX2-V66 die.JPG
| border="1" class="wikitable"
|+ Models of Cx486DX2 ! Model/Feature ! Bus Speed ! Clock Frequency ! Cache ! Voltage ! Notes |
| Cx486DX2-50
| 25 MHz || 50 MHz || 8KB || 5 Volts DC || Available with permanently attached heatsink. |
|---|
| Cx486DX2-66
| 33 MHz || 66 MHz || 8KB || 5 Volts DC || Available with permanently attached heatsink. |
| Cx486DX2-V66
| 33 MHz || 66 MHz || 8KB || 3.3 or 3.45 Volts DC || Low Voltage. Available with permanently attached heatsink. |
| Cx486DX2-V66 PQFP
| 33 MHz || 66 MHz || 8KB || 3.3 Volts DC || Available with permanently attached heatsink, Low Voltage. QFP Package. |
| Cx486DX2-80
| 40 MHz || 80 MHz || 8KB || 5 Volts DC || Available with permanently attached heatsink. |
| Cx486DX2-V80
| 40 MHz || 80 MHz || 8KB || 3.45 or 4.0 Volts DC || Low Voltage. Available with permanently attached heatsink. |
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.{{cite web |url=https://www.cpushack.com/2012/09/06/intel-vs-the-world-the-338-patent/ |title=Intel VS the world - '338 patent cases|date=6 September 2012 }} 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.{{cite web |url=https://caselaw.findlaw.com/us-federal-circuit/1139896.html |title=International Business Machines Corporation, Plaintiff-Appellee, v. INTEL CORPORATION (1996)}} 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 devices, such as those using the PC/104 form factor.{{cite web |url=http://www.getmis.com/catalog/p_pia-647---discontinued-product.html |title=PIA-647 - An SBC based on the STPC |archive-url=https://web.archive.org/web/20141107110319/http://www.getmis.com/catalog/p_pia-647---discontinued-product.html |archive-date=2014-11-07 |url-status=dead}} One notable difference between the STPC and other Cx486 processors is the Host Clock which operates at 66 MHz for STPC devices.{{cite web |url=https://www.datasheetcatalog.com/datasheets_pdf/S/T/P/C/STPCI2.shtml |title=STPC ATLAS DATASHEET / X86 PC COMPATIBLE INFORMATION APPLIANCE SYSTEM-ON-CHIP - SGS Thomson Microelectronics}} 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 processors based on AMD's Enhanced Am486 core as used in the Am5x86 which still relied upon a 33 MHz external clock.{{cite web |url=http://datasheets.chipdb.org/AMD/Elan/SC5x0/SC520/520tech1.pdf |title=AMD ÉlanTMSC520 Microcontroller Technical Details}}