🚀 go-pugleaf

Would someone please take a shot at explaining this to me:

A Mac Plus has a 68000 running at 8 Mhz. That's a clock time of ~126 ns. It
has 120 ns memory chips. Things seems clear in this case: It takes one clock
cycle for each memory access. OK.

A Mac SE/30 has a 68030 running at 16 Mhz. That's a clock time of ~63 ns. When
looking for SIMMs, I found 100 ns, 80 ns, and (I think) 70 ns versions. No-one
I have talked to has heard of 60 ns SIMMs.

If the ram takes 70 ns to answer, and the clock is 63 ns, shouldn't it take
two clock cycles to fetch a long word?

If that is the case, why sell faster than 120 ns ram, if 60 ns isn't available?
It would seem that 70ns acts just like 80ns acts just like 100ns.  Does the
68030 effectively run at 8 Mhz from RAM, and 16 Mhz from its cache? Finally,
why would 100ns RAM be _required_, like, 120 ns SIMMs won't work at all?
Do 60ns 1Mbit DRAMs exist, and how much are they? The 120ns variety are down
around $120/SIMM now, apparently.

If that is not the case, how is memory access asynchronous with the system
clock?

-Dazed and Confused
-Iain McClatchie