sim72-fp - timing &C

[legacy]

sim30's are simple, you have { ras, cas }, while sim72-fp's looks more complex and I am a bit confused because they have { { RAS0 RAS1 RAS2 RAS3 } { CAS0 CAS1 CAS2 CAS3 } } but I have seen designs where only { ras0 ras2 } are used, and connected together, while { ras1 ras3} are simply unconnected.

is there a clear and neat document about this?

[legacy]

There are documents on 72SIMM around the internet but they are confusing. Yesterday I found in a street market a copy of "The indispensable PC hardware book", and from what I have understood, the assignment of RASx and CASx are made according to single-sided or double-sided. The book gives examples, and it seems that if the SIMM is singled-sided, then only RAS0 (lower 16 bits) and RAS2 (upper 16 bits) are used, while RAS1 and RAS3 are for the 2nd side of the double-sided SIMM card.