Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!usc!polyslo!rcfische
From: rcfische@polyslo.CalPoly.EDU (Raymond C. Fischer)
Newsgroups: comp.sys.mac.hardware
Subject: Re: IIci + 8Mb != more speed
Message-ID: <25d88b45.2cea@polyslo.CalPoly.EDU>
Date: 13 Feb 90 22:33:41 GMT
References: <22499@mimsy.umd.edu>
Reply-To: rcfische@polyslo.CalPoly.EDU (Raymond C. Fischer)
Distribution: usa
Organization: Cal Poly State University -- San Luis Obispo
Lines: 33


In article <22499@mimsy.umd.edu> folta@tove.umd.edu (Wayne Folta) writes:
>We just installed 4Mb of memory in Bank B of our IIci, resulting in an 8Mb
>machine.  The problem is that I was convinced by the Mac magazines that
>adding memory in Bank B would decrease video RAM contention and thus speed
>the IIci up.  I have found no such speed increase.
[edited]
>So what's up?  Was the Bank B magic a lie?  Is my test too simple?  Was
>the speedup only for graphics-intensive programs?

No, the bank B magic is not a lie, no your test is not really to simple,
and no, it's not just for graphics.

The Mac IIci uses bank A as video memory.  Reading of the memory by
the video circuitry prevents the 68030 from getting unrestricted access
to that memory.  This is why the Mac runs slower when you switch to 8-bit 
video; more memory accesses go to video.  Bank B memory doesn't have 
this problem.  Video never reads from bank B and so the '030 can have 
unimpeded access to the memory.

By running your programs IN bank B memory, your avoid contention with
the video.  The processor runs from bank B and the video from bank A.
However, the Mac still loads programs into RAM from the bottom upward.
Thus, on an 8 meg machine, your program is probably still running in
the lower 4 meg (i.e., bank A).  If you can get it to run in bank B,
then you should see a speedup.  This is also why 5meg is such an
attractive configuration for the IIci.  1meg in bank A is usually
used up by the video and system leaving only the 4 meg in bank B for
running programs.


Ray Fischer
rcfische@polyslo.calpoly.edu