4 Megg SIMMs. Should I or shouldn't I?

[Eric Smith]

In article <1990Nov6.041551.2038 at panix.uucp> alexis at panix.uucp (Alexis Rosen) writes:

>   In any event, you probably don't want to do this. The money you spend on the
>   board could instead go to 4MB SIMMs. Furthermore, access to that RAM would go
>   over NuBus, and would thus be _slow_ compared to regular memory. (I seem to
>   recall a minimun 300ns access time, though I'm not sure. That would make it
>   about 4 times slower, although you might make some of it back on wait states
>   you wouldn't need.)

300 nS is the minimum CYCLE time.  On a Macintosh IIx, the RAM on the logic
board is run with 255.3 nS cycles, which is not that much faster than the
maximum NuBus speed.  Then again, there is a synchronization delay to access
NuBus, and many (most?) NuBus cards don't run a maximum theoretical speed.

I don't know exactly how fast the Macintosh IIfx runs DRAM cycles, but it
can't be much faster than 200 nS (most 80 nS RAMs are spec'd for about
190 nS cycles).  I would expect that main RAM access on the IIfx would be
about twice the speed of a fast NuBus card.

--
Eric L. Smith      Opinions expressed herein do not necessarily reflect those
esmith at apple.com   of my employer, friends, family, computer, or even me!  :-)