Q Lately I have been searching around for my next PC upgrade specification. For the work that I do I have decided to go for a Cyrix 6x86 PR200 or PR233. However, I have discovered some abnormalities when shopping around at Melbourne swap meets for pricing. These concern the Cyrix 6x86 Socket 7 processor.

A IBM is working in partnership with Cyrix to produce the 6x86 processor. Cyrix designs the processor and IBM manufactures it. They are then tested and packaged separately by both companies who label the processor accordingly. But the processors are identical in design. Differences may exist in the quality of testing, but this should be high in both cases.

The reason why you have two different PR200MX processors is the Pentium Rating (see The IBM/Cyrix relationship above). The PR number is different from the actual clock speed of the processor. The confusion stems from the fact that there are two IBM/Cyrix processors with the PR number 200. One has a clock speed of 150MHz and bus speed of 75MHz, and one has a clock speed of 166MHz and a bus speed of 66MHz. Despite different processor speeds, both processors will run programs at roughly the same speed. However, the 75MHz bus speed means that the processor can talk to external memory more quickly than the 66MHz processor.

Caption: IBM/Cyrix performance specifications

From this point of view, 75MHz bus speed is probably better, but it may not be worth the extra $100 that you say they are charging. Please see the table for a list of available IBM/Cyrix processors, their PR numbers and their clock and bus speeds.