The issues on backwards compatibility of PC133 and PC100 with PC66 is as old
as the hills. PC-66 came in two distinct varieties: 2 clock and 4 clock,
whilst PC100/PC133 is 99.99% 4 clock. If the machine requires 2clock PC66
then 4 clock PC100 and PC133 will not work. This was an accute problem with
the TX chipset.
PC66 is in usually far more expensive than PC100/PC133 as the modules/chips
have not been manufactured for over 4 years.
Glen
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