2.17 What speed SIMMs do I need?
Description
This item is from the PC Hardware FAQ, by Willie Lim and Ralph Valentino with numerous contributions by others. (v1.25).
2.17 What speed SIMMs do I need?
[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]
There is no reliable formula for deriving the required RAM speed from the clock rate or wait states on the motherboard. Do not buy a motherboard that doesn't come with a manual that clearly specifies what speed SIMMs are required at each clock rate. You can always substitute *faster* SIMMs for the ones that were called out in the manual. If you are investing in a substantial quantity of RAM, consider buying faster than you need on the chance you can keep it when you get a faster CPU.
That said, most 25 MHz and slower motherboards work fine with 80 ns parts, most 33 MHz boards and some 40 MHz boards were designed for 70 ns parts, and some 40 MHz boards and everything faster require 60 ns or faster. Some motherboards allow programming extra wait states to allow for slower parts, but some of these designs do not really relax all the critical timing requirements by doing that. It's much safer to use DRAMs that are fast enough for the no-wait or one-wait cycles at the top end of the motherboard's capabilities.
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