Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!mcsun!hp4nl!cbmnlu1!cbmnlux!ecl014!ronald
From: ronald@ecl014.UUCP (Ronald van Eijck)
Newsgroups: comp.sys.amiga.hardware
Subject: CHIP bus speed (was Re:  RAMs for ehe A3000)
Message-ID: <ronald.3804@ecl014.UUCP>
Date: 5 Jun 91 16:58:45 GMT
References: <618.28484461@busker.fidonet.org> <22124@cbmvax.commodore.com>
Organization: R&R Software
Lines: 34

In article <22124@cbmvax.commodore.com> daveh@cbmvax.commodore.com (Dave Haynie) writes:
>No, the CPU access speed is the same, just 32 bits wide rather than 16 bits
>wide as on the A2000 and A500.  It doesn't make sense to refer to Chip RAM
>access as "7.16MHz" or "25MHz", since they really doesn't say anything about
>what's happening.  The CPU always runs at 25MHz (in a 25MHz system), it just
>takes waits states when accessing Chip RAM.  The Chip bus is synchronous to
>Agnus.  It runs a 560ns cycle, consisting of two 280ns memory accesses, one
>of which the CPU can use if the blitter, copper, or video fetch don't lock it
>out.  The only way to let the CPU in for more cycles is to double the memory
>speed during the CPU access window.  That would require a 140ns cycle and a
>faster Agnus.  That's not quite attainable yet.  When 60ns DRAMs become as
>cheap as 80ns, that may be something to consider.  Software has done more for
>system performance that this would, anyway, by moving as much as possible into

Sorry to disagree with the master himself but my calculations give very
impressive numbers for a double speed chip memory system.

Asuming that you are using a hires 4 planes overscanned video the number of
memory slots the CPU/Blitter can use would be 8 (that is eight) times better
if the chip bus was 2 times faster. This would make a lot of programs fly in
this mode. The problem is that if the chip bus was 2 times faster we would
all want 256 colors and have a system the same speed we have now.
(So dave If you can find cheap 60 ns rams start working ;-)

>Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
>   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
>    "This is my mistake.  Let me make it good." -R.E.M.

--
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  |  Ronald van Eijck                  {eunet!}hp4nl!cbmnlux!ecl014!ronald  |
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