[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Multiple Address versus single AS Operating System
> 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. Actually, this is a separate issue to whether the OS itself presents a MAS or SAS model. All widely used general purpose OSes are MAS (eg. UNIX, Linux, Windows). When the cache is virtually indexed, you can still use a physical "tag". This means that there's no ambiguity between address spaces when doing a lookup, *except* when sharing pages between address spaces (in which case a MAS OS must be careful to avoid the same data being stored in two different cache locations). > 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. The hardware just has to have an MMU so that we can do virtual memory. Exactly how the hardware behaves is orthogonal to whether the OS is SAS or MAS - you could implement either. In a SAS OS, all processes coexist within one linear address space, starting at 0 and going up to 2^n -1 (for platform with n bit addresses). All they exist within the same address space, the MMU is still used to provide the usual protection between them. In a MAS OS, every process sees its own private linear address space from 0 to 2^n -1. This is the familiar model we get with Unix and other systems. HTH, Mark _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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