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From: hmthaker@wateng.UUCP
Newsgroups: comp.arch
Subject: Will caches ever become obsolete?
Message-ID: <3182@wateng.UUCP>
Date: Sun, 1-Mar-87 23:41:12 EST
Article-I.D.: wateng.3182
Posted: Sun Mar  1 23:41:12 1987
Date-Received: Mon, 2-Mar-87 19:39:04 EST
Distribution: comp
Organization: Electrical Engineering Dept., University of Waterloo
Lines: 35
Keywords: cache, coherence problems


      I have a question concerning caches.  Currently,
caches are used, either in uniprocessors, or multiprocessors,
because the time a microprocessor takes to execute an
instruction is much smaller than the time to reference
main memory.  Thus, a cache is used to match the speed
difference (the cache is usually as fast as the microprocessor).

      Thus, it is evident that a cache can very dramatically
improve the throughput of a microprocessor.  For multiprocessors,
much research is being conducted to find efficient algorithms
for multi-cache consistency.

      Multi-cache consistency problem arises when, say a
block of data resides in the caches of processors A, B, and
C.  Then, if processor B decides to write to that block,
it must inform A and C that their copies of the block are
no longer valid.

     My question is, then, with the current improvements in
memory chips (ie. faster access, and greater densities), does
anyone forsee a time in the distant future (> 3 or 4 years)
that the speed of say, a 1Mb chip will be comparable to that
of say a 1Kb ECL chip used in current caches?

     In other words, will all the research being conducted
for the cache coherency problems be a waste?  Could the
research done for multi-cache coherency be applied elsewhere?

Thanks.

             Hemi Thaker

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