PC100 SDRAM Warning

Many vendors are now offering PC100 SDRAM for sale. Customers are beginning to buy this with the intention of using it later in their BX chipset boards. What is not well understood is that the PC100 SDRAM spec has undergone several revisions in the past few months.

The latest spec is 1.0, which has introduced at least one compatibility issue. Many vendors are building to the .8 or .9 spec, which will *not* work on BX chipset boards, in some cases. Be aware of what you are buying and make sure your vendor knows which spec he/she is selling

The most important change between the .8/.9 spec and the 1.0 spec is that the clock lines have changed in regards to which banks they control. The net result is that some, if not all single-sided modules will not be cross-compatible. The .8/.9 spec modules will work on the non-BX chipset motherboards, but not on the BX, and vice-versa. Again, this issue is for single-sided modules primarily (16MB and 64MB).

Basically, prior to spec 1.0, Clock lines 0 & 1 controlled the first bank while clock lines 2 & 3 controlled the second bank. Intel found that this created some ‘interference’ in the signal at high frequencies, and decided to change the spec for their new chipset to ensure stability at 100MHz operation. Now, spec 1.0 calls for clock lines 0 & 2 / 1 & 3 to control the corresponding banks.

Before buying any PC100 SDRAM, make sure you understand what your needs are, and purchase the SDRAM what will fit them. Don’t get caught up in the marketing hype and buy the cheapest SDRAM, or you might find later that you are spending twice as much

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