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Re: R4xxx Cache size.

To: riscy@pyramid.com
Subject: Re: R4xxx Cache size.
From: Andreas Busse <andy@resi.waldorf-gmbh.de>
Date: Tue, 10 Aug 93 10:58:48 +0200
Reply-to: riscy@pyramid.com
Sender: owner-riscy@pyramid.com
> >    The R4xxxx has a larger internal cache.
> >
> >R4000 : 8K I, 8K D
> >R4400 : 16K I, 16K D
> >
> >The maximum imposed by the R4000 architecture is 32K each for the primary
> >cache.  I don't know about the 4200 since I don't have a data book in front
> >of me like I do for the NEC Vr4000 and Vr4400, PC, SC, and MC variants :-)
> Huh? Does that mean that the ARCHITECTURE defines a maximum CACHE size?
> According to current definitions here at the computer architecture group,
> cache size is an implementation aspect, and shouldn't be visible at the
> architectural level.
> -----
> This means that the R4xxx has a bad design: the design mixes implementation 
> with architectural features. The R4000 isn't as clean as we thought. This
> means that we can't use the R4000 as the processor.... :-)
> -----

Oh, please stop that noise. I don't know who told you that the
cache size of a R4000 is limited to 32+32k. Can you tell me how it
would then be possible to add a secondary cache ????
The limitation, if there is one, is given by the chip size, not
by any architectural problem !
If you would take a look at the R4200 layout, you would see that
more than 70 percent of the chip space is used by rams !


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