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Re: [Xen-devel] Multiple Address versus single AS Operating System

To: VISHAL MALIK <sunnymak04@xxxxxxxxx>
Subject: Re: [Xen-devel] Multiple Address versus single AS Operating System
From: Hollis Blanchard <hollisb@xxxxxxxxxx>
Date: Tue, 21 Jun 2005 16:41:47 -0500
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On Thu, 2005-06-16 at 10:42 -0700, VISHAL MALIK wrote: 

>         I was wanted to confirm and also find out what people think is
>         the main difference 
>         between multiple address space Operating systems and single
>         address space 
>         operating systems. 
>         Intel is a MAS platform as the cache's are physically indexed
>         whereas 
>         most of the RISC processors have Single Address space
>         Operating system 
>         architecture due to the fact that the caches are virtually
>         indexed. 
>         (in a VI-cache, you access the cache and tlb at the same
>         time). 
>         I have been trying to ask if the above assertion is correct or
>         we can have 
>         a MAS-OS on RISC platforms too? And if yes, then from a
>         hardware 
>         perspective, what is the defining criteria to have a SAS-OS or
>         MAS-OS. 

I don't understand your question, but I can say for PowerPC:

        icache          dcache
        index/tag       index/tag
405GP:  V/P             P/P
604:    P/P             P/P
970:    V/P             V/P

So your statement that most RISC processors are virtually indexed is a
bit of an oversimplification I think.

Hollis Blanchard
IBM Linux Technology Center

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