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Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!gem.mps.ohio-state.edu!ginosko!uunet!crdgw1!crdos1!davidsen
From: davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr)
Newsgroups: comp.sys.ibm.pc,comp.unix.i386
Subject: Re: Micronics 386 motherboards
Message-ID: <969@crdos1.crd.ge.COM>
Date: 10 Oct 89 15:41:51 GMT
References: <22861@cup.portal.com> <157@sherpa.UUCP>
Reply-To: davidsen@crdos1.UUCP (bill davidsen)
Followup-To: comp.sys.ibm.pc
Organization: GE Corp R&D Center
Lines: 31

In article <157@sherpa.UUCP>, rac@sherpa.UUCP (Roger Cornelius) writes:

|  Can you explain interleaved memory and what it's advantages are?  

  Dynamic RAM has an access time and a cycle time. If you read one byte
from the RAM it will take the access time, say 60ns. However if you go
right back to that chip you can't get data in less than the cycle time,
say 80ns. By putting the odd bytes in one bank and the even in another
you avoid going to the same chip for two bytes in consecutive locations.

  High performance memory may be interleaved more than two ways to
maximize the chance of hitting another chip when accesses are done,
random or sequential.

  When Tandy released their first 386 machine some magazines got 20%
more performance on the CPU than others. It seems that with only 1MB the
interleave was disabled, giving 1 w/s on each access. There were claims
that Tnady had sent out "souped up" machines for benchmarking, but these
were proved false when adding memory to the "slow" machines made them
fast. Many machines today require adding memory two banks at a time and
don't offer disabling of interleave.

  Caching is another way of reducing the effective number of wait
states, as is column static memory. Let some EE write the definitive
posting. Oh yes, this is true for UNIX and DOS both.

-- 
bill davidsen	(davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen)
"The world is filled with fools. They blindly follow their so-called
'reason' in the face of the church and common sense. Any fool can see
that the world is flat!" - anon