Subject: Re: cache
To: Joe Smith <jms@tardis.Tymnet.COM>
From: Jukka Marin <email@example.com>
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
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! ;-)
---> http://www.jmp.fi/~jmarin/ <---