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Re: r10000 boards

To: linux-mips
Subject: Re: r10000 boards
From: khp@dolphinics.no (Kai Harrekilde-Petersen)
Date: Wed, 2 Apr 1997 07:57:45 +0200 (MET DST)
In-reply-to: <Pine.LNX.3.95.960401194650.11590A-100000@ravage.labs.gmu.edu> from Ryan Rafferty at "Apr 1, 96 07:49:54 pm"
Ryan Rafferty writes:
> 
> On Wed, 2 Apr 1997, Systemkennung Linux wrote:
> > A good RAM interface is a much more effective mean to accelerate a
> > system than caches especially when you have an application that
> > has a working set that exceeds the cache size.  The Magnum's RAM
> > interface may be slow by today's standards but it was very fast
> > at it's time.
> 
> Ok, that's cool.  But then why do computer manufacturers still incorporate
> cache into today's machines instead of using blazing memory interfaces?

Because making a 'blazing' memory subsystem is difficult.  Very
difficult.  Actually, I will claim that the memory subsystem is *the*
determining factor when it comes to system performance (when your
application touches a lot of memory - which is quite common).

Moore's Law has been used to make CPUs go really fast and DRAMs very
large.  Thats a fact of life.  If you read comp.arch, they will refer
to this problem as 'the memory wall' (The latency of the P6 "Orion"
450GX chipset is ~190 cpu clocks).  All these new memory organizations
(SDRAM, RDRAM, SLDRAM, EDRAM, CDRAM, ad nauseum) are trying to reduce
the problem.

Also, most computer projects have a set goal of price and performance.
In a previous life at Terma (Hi Theo, still around?) I designed an
embedded Xterminal, which used the R4600.  We didn't use a cache, for
two reasons: price and board-space.  Board space was critical; we have
100+ chips on a standard 6U VME board.  Instead we used an interleaved
memory system, which achieved 100MByte/sec read/write performance with
a 33MHz bus.  (No asics; just discrete registers and a large epld).


Kai
-- 
Kai Harrekilde-Petersen    <khp@dolphinics.no>    #include <std/disclaimer.h>
http://www.dolphinics.no/~khp/          Linux: the choice of a GNU generation
"Argue for your limitations, and sure enough - they're yours" --Richard Bach.

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