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Cyrix and IBM 6x86MX 6x86L 6x86KV and
MII Chip ID guide
Finding information on these chips is very difficult. Cyrix
has been bought by VIA and datasheets are no longer available. Cyrix, IBM,
ST and National all made the Cyrix line of CPUs. Each had their own marking
system and ID codes for their chips. This makes Identifying them quite hard.
Not to mention a single performence rating having 3 or 4 speeds and made on
3 different silicon processes. Thank goodness there werent many different
packages. Cyrix 6x86 CPUs spanned 220MHz but their PR values spanned 343 (90433).
IBM
Cyrix
PR Values Table
Raw Data Used in this Guide
Cyrix Time Line
IBM
IBM CPUs have the ID markings on top. They are a bit cryptic
but once you look at them they really do make sense. Please note that a IBM
6x86MX is the same CPU as a Cyrix 6x86MX or a Cyrix M2. IBM chose not to change
the name of the CPU while Cyrix did to better compare it to the Pentium II
and K6II.
IBM 6x86MX  IBM 6x86L  IBM 6x86 
IBM26x86MXmVcPRxxxpr xxx = Performance Rating m = Multiplier p = package c = core voltage r = mask revision 
IBM26 6x86LmVcPxxxpr m = Multiplier c = Core Voltage p = Package r = Revision 
IBM26 6x86mVcPxxxpr xxx = Performance Rating m = Multiplier c = Core Voltage p = Package r = Revision 
Cyrix
Cyrix CPUs are even harder to identify. They follow the same PR scheme as
IBM but the codes are harder to understand. the ID code for a Cyrix is located
on the BOTTOM of the chip on all but the black top CPUs and Mobiles. Cyrix
CPUs were produced on .35, .30, .25 and .18 micron processes. Quite often
a single PR will be made in no less then 3 process technologies and 2 speeds
with 2 bus speeds. All 6x86MX and M2 CPUs are 2.9 Volt. The exception to this
is that all .18 micron M2s are 2.2 Volts.
Cyrix
6x86MX and M2 (MediaGX CPUs follow a slightly different scheme) 
National Produced
MII 
Black Top and
Late Model MII (All are made by National) 
SGSThomsan 

6x86 
Later Model Black Top 


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PR Rating  Bus (MHz) 
CPU Core (MHz) 
Clock Multiplier 
PR90  40  80  2x 
PR100  40  80  2x 
PR120  50  100  2x 
PR133  50  100  2x 
PR133  55  110  2x 
PR150  60  120  2x 
PR150  50  125  2.5x 
PR166  66  133  2x 
PR166  55  138  2.5x 
PR166  50  150  3x 
PR166  60  150  2.5x 
PR200  75  150  2x 
PR200  55  165  3x 
PR200  66  166  2.5x 
PR200  60  180  3x 
PR233  75  188  2.5x 
PR233  66  200  3x 
PR233  83  166  2x 
PR266  66  233  3.5x 
PR266  75  225  3x 
PR266  83  208  2.5x 
PR300  75  225  3x 
PR300  66  233  3.5x 
PR333  83  250  3x 
PR350  83  250  3x 
PR366  100  250  2.5x 
PR400  95  285  3x 
PR433  100  300  3x 
If you know of any more Cyrix ID info etc. Please email me and I will add
it