What is pc100 specification..?

as far as I think and know, you are talking abt PC 100 Rams. These were the synchronous Drams or the SDRAMs that were used in older pcs. No longer in use these days.
What exactly do you want to know about them ?

Now i found the answer opty,
People assumes that 10ns(clock speed) module definitely will able to run on a 100MHZ system(Because reciprocal of 10ns is 100MHZ).
But in practice you required slightly higher than what is required.So 10ns will perfectly fit on 85MHZ system.
So 100MHZ system required more faster memory than 10ns(clock speed).
That is why PC 100 specification was developed.

Actually PC 100 specification is the one you have to pass in order to use any SD RAM on your motherboard.
But not this only give you the full independency.
Other internal timing charectristic that must be meet in order to have a module certified as PC 100 compliant.
It's realy a good idea to ensure that any SD RAM you intended to use on 100MHZ system bus motherboard is in fact PC 100 specification compliant.