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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Cyrix introduced its MMX-enabled 6x86MX processor, previously code-named M2, on May 30, 1997. It launched in PR166, PR200 and PR233 grades, used a Socket 7-compatible pinout, and required a motherboard that supported its split-rail power. Its PR number described a performance class—not its actual clock speed.
When did Cyrix launch the 6x86MX?
Cyrix introduced the 6x86MX on May 30, 1997; EDN reported the launch on June 2, 1997. The processor had previously been known by the code name M2. Cyrix announced three grades at launch: PR166, PR200 and PR233. A PR266 was expected in the fourth quarter of 1997, but that was a planned future grade in the launch announcement, not one of the three launch models. EDN’s June 1997 launch report
What did the PR grades mean, and how fast did the chips run?
The PR grades were performance ratings, not the processors’ clock frequencies. Cyrix’s technical brief gives the bus and core clock pair for each launch grade:
| Launch grade | Bus clock | Core clock | Announced price |
|---|---|---|---|
| PR166 | 60 MHz | 150 MHz | $190 in 1,000-unit quantities |
| PR200 | 66 MHz | 166 MHz | $240 in 1,000-unit quantities |
| PR233 | 75 MHz | 188 MHz | $320 in 1,000-unit quantities |
The prices were launch-era announced prices reported by EDN for purchases of 1,000 units; they are not current used-processor prices. EDN’s June 1997 launch report lists the prices, while Cyrix’s 1997 technical brief lists the bus and core clocks.
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What were the 6x86MX’s main features?
MMX-compatible multimedia instructions
Cyrix said the 6x86MX could process 57 new multimedia instructions compatible with MMX technology. That describes instruction support; it does not by itself establish how fast the processor would run every multimedia application. Cyrix’s 1997 6x86MX data book
Cache and branch prediction
The chip included a 64-KByte unified write-back cache and a 512-entry branch target buffer. “Unified” means the listed cache was not described as separate instruction and data caches. Cyrix’s data book also specifies a two-level translation lookaside buffer (TLB): 16 entries at L1 and 384 at L2. These are architectural specifications, not a guarantee of a particular application benchmark result. Cyrix’s 1997 technical brief and data book
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Was the Cyrix 6x86MX compatible with Socket 7?
Yes, the listed PR166, PR200 and PR233 parts were Socket 7 pinout compatible, and Cyrix explicitly lists the PR233GP as Socket 7 compatible. But a matching socket alone is not enough to establish that a processor will work in a particular vintage PC. The 6x86MX used split-rail power: approximately 2.8–2.9V for the core and 3.3V for I/O. A motherboard therefore needs suitable voltage regulation as well as the correct socket pinout; BIOS support should also be checked for the specific board and processor. Cyrix’s 1997 technical brief and data book
How should you choose a 6x86MX for a vintage PC?
Start with the motherboard, not the PR rating. Confirm the exact processor marking and board documentation, then check socket pinout, split-voltage support and BIOS compatibility. Cyrix’s published specifications establish the launch models’ clocks and Socket 7 pinout, but do not establish compatibility with every Socket 7 motherboard.
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- Check voltage regulation: verify that the board supports roughly 2.8–2.9V core voltage and 3.3V I/O for the processor.
- Check BIOS support: confirm the board BIOS recognizes the 6x86MX and the intended grade.
- Match clock settings: use the bus/core pair for the specific grade—60/150 MHz for PR166, 66/166 MHz for PR200 or 75/188 MHz for PR233.
- Buy for the system you have: a higher PR grade does not mean the processor runs at that number of megahertz, and the published figures alone do not determine performance in a particular workload.
For a parts search, “Cyrix 6x86MX PR233 Socket 7 processor” is a precise query. A processor listing or a Socket 7 motherboard listing is not proof of compatibility: verify the board’s voltage regulation, BIOS support and pinout against its documentation. Current inventory, seller claims, prices and part condition can vary and are not established by the 1997 specifications.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What performance claims did Cyrix make?
Cyrix positioned the processor as a lower-cost alternative to high-end systems of the period. EDN quoted the company saying: “The 6x86MX processor enables PC manufacturers to deliver the performance and features of expensive Pentium II systems for under $2,000.” The report also describes Cyrix’s Winstone 97/98 parity claims. Those are period company claims, not universal results or a controlled cross-vendor comparison. The cited material does not provide a single comparable test table covering the 6x86MX, Intel Pentium MMX, Pentium II and AMD K6. EDN’s June 1997 launch report
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