🚀 go-pugleaf

in article <16327@shemp.CS.UCLA.EDU>, korfhage@CS.UCLA.EDU says:
> 
>    What I wonder, though, is just how much performance you can get from the
> faster clock speed, given that most macs have 120 ns rams? I asked about this,
> and was told that the 25 and 33 Mhz models would run with 1 wait state using
> 120 ns memory, and 0 wait states with 100 or 80 ns memory. Is there anyone
> out there with some 68030 hardware knowledge who can say if this is
> reasonable? 

If they're talking about accessing Mac II's motherboard memory, which I assume
doesn't do any special tricks, I'd say no, this sounds quite unreasonable.  The
best you could do with 100ns parts and a 25MHz 68030 is about 2 wait states.
If you consider how fast the '030 could really be going at 25MHz in synchronous
mode, that's actually 3 wait-states.  However, you can get performance up to
more like 0 or 1 wait state using various paging and/or interleaving techniques.
Lots of the faster '386 machine use these techniques (they, of course, needing all
the help they can get).  The other solution would, of course, be to supply your
fast '030 add-in with an external data and instruction cache, which would then
give you maybe an effective rate closer to 0 or 1 wait state.  That of course
requires that the Mac OS support full caching.

> I though that Mac II's had two wait states built in (it may only be one). 

The plain old Mac II's gonna have 1 wait state for the PMMU, that's built into
the PMMU design.  Other than that, I guess you need a Mac hardware expert.

>    Also, I have wondered if anyone sells the PC boards that make up SIMMs?

A company called MicroBotics sells pre-made DIP modules that fit a SIMM socket,
but I don't know if they sell just the bare boards or not.

>    Willard Korfhage
-- 
Dave Haynie  "The 32 Bit Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {ihnp4|uunet|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
		"I can't relax, 'cause I'm a Boinger!"