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From: iand@mullian.ee.mu.oz.au (Ian Robert DOBSON)
Newsgroups: comp.sys.mac.misc
Subject: Re: Speeding up a IIsi
Message-ID: <6796@munnari.oz.au>
Date: 18 Feb 91 01:11:41 GMT
References: <60103@eerie.acsu.Buffalo.EDU> <ingemar.666802842@stuart>
Sender: news@cs.mu.oz.au
Reply-To: iand@mullian.ee.mu.OZ.AU (Ian Robert DOBSON)
Organization: Dept. of Electrical Engineering, University of Melbourne
Lines: 29

>2) The IIsi has a strange memory configuration. Basically, the first 1 meg
>is on the board, and it is used as video ram *but also as general ram*. This
>means that when the work is made in this memory, the CPU and video both must
>access the same memory, and therefore wait for each other. The measurements
>I've made imply that it is slowed down by almost 50%! (You say 5 times. That
>sounds like too much to me, unless they are *very* graphic intensive.)

When I bought my IIsi, I found 8 bit mode to be extremely slow compared to 4
bit mode (and b/w etc.)  This problem can be alleviated somewhat by getting
a RAM upgrade to 5mb if you have a 2mb machine at present.  This reduces the
chance of your application being in the shared RAM bank and speeds up the
machine considerably.
   The other thing you should do is run MultiFinder.  When MultiFinder is
running, it tries to avoid using the video switched RAM as much as possible,
while uniFinder doesn't know about it so uses it first.

I have used a speed test program and found that the general CPU speed will
increase by about 60-70% by upgrading from 2Mb to 5Mb RAM (in the 256
colour mode), although graphics intensive applications would probably not
find that order of performance increase.

As a side point, the b/w mode using the built-in video is faster than using
a NuBUS card, because there isn't a whole lot of conflict with memory usage
with 1 bit/pixel, and a direct write to built-in video RAM is much faster
than going through NuBUS.

Ian R. Dobson
University of Melbourne
iand@mullian.ee.mu.OZ.AU