Subject: Re: cache
To: Joe Smith <jms@tardis.Tymnet.COM>
From: Jukka Marin <>
List: amiga
Date: 03/26/1996 08:17:16
> > However, as I was 
> > told before that the memory access in stock Amiga ( A4000 in my case )
> > is quite slow.
> You have been misinformed.  Memory access in the Amiga between the CPU and
> fast RAM is quite fast.  So fast, that adding an L2 cache will not make it
> any faster.

The A4000 FAST RAM is pretty slow, indeed.  It is slower than the FAST RAM
of A3000.  However, the A4000/40 has a faster CPU which really suffers
from the slow memory.  The performance is probably around 50% of what it
_could_ be (I've heard that the Motorola VME boards are very fast (but then,
the also cost a lot)).

> Memory access between the Amiga CPU and the "chip" RAM (also known as the
> "graphics" RAM) is slow because the CPU has to go through the Amiga's custom
> graphics chips to get to the graphics RAM.  Adding an L2 cache there is not
> possible.

Actually, the CPU doesn't go through the custom chips (at least on A3000 it
doesn't).  But you're right, you can't use a cache with CHIP RAM.
> You seem fixated on the idea that adding a Level-2 cache to the Amiga will
> fix all of your problems.  It doesn't work that way.  Please accept that
> fact and move on.

Well, it would be nice to see what a fast cache could do.  The wait states
we have now certainly slow down the CPU (try turning off the internal cache
to see! ;-)



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