Povl Pedersen writes, "There is something more about the 72-pin SIMMs that you should note. They are all 32-bit, as opposed to the old 8-bit SIMMs. This means that you can upgrade one slot at a time. On older 32-bit data bus-equipped machines (all Mac II series and the SE/30) you need to fill four SIMM slots at a time."
Information from:
Povl H. Pedersen -- pope@imv.aau.dk