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From: phil@amdcad.UUCP (Phil Ngai)
Newsgroups: net.arch
Subject: Re: VERY LARGE main memories; HOW M
Message-ID: <13214@amdcad.UUCP>
Date: Thu, 2-Oct-86 01:17:34 EDT
Article-I.D.: amdcad.13214
Posted: Thu Oct  2 01:17:34 1986
Date-Received: Sat, 4-Oct-86 04:09:17 EDT
References: <1128@tekig5.UUCP> <5100141@ccvaxa>
Reply-To: phil@amdcad.UUCP (Phil Ngai)
Organization: Advanced Micro Devices, Sunnyvale, California
Lines: 37

In article <5100141@ccvaxa> aglew@ccvaxa.UUCP writes:
>
>>This is another problem with virtual memory - central memory is
>>starting to get cheaper and bigger than the disk memory.  The biggest
>>disk drive available with a Cray these days is a DD-49 (holds about
>>151 MW).  One memory image of the 4GW Cray 3 would fill 26 DD-49s to
>>capacity.  What are you going to operate virtual memory out of?
>>
>>J. Giles
>>Los Alamos
>
>Main memory will be as much high speed RAM as you can afford.
>Virtual memory will be slightly slower speed but less expensive RAM.

In fact, the Cray 2 uses ordinary dynamic RAMs for main memory. These
are the same type of devices your IBM PC uses. Of course, Cray
interleaves them many ways to get the data bandwidth needed. But the
point is, main memory is already made out of the most cost effective
memory devices available. There is no "slower speed but less expensive
RAM". Note that I am talking about main memory, not cache, which is
made of expensive high speed devices. As cache is handled by hardware,
it is not relevant to a virtual memory discussion.

There was a claim that RAM is getting cheaper than disk. Assume 474Mb
eagle at $10,000. This yields $2E-5 per byte. Assume 256Kbit DRAM at
$2.56. (see 10/1/86 San Jose Mercury News Fry's Electronics ad) This
yields $8E-5 per byte.

Rotating machinery is still cheaper than silicon.

-- 
 In Arizona they brag about how much water it takes to maintain their
lawns and golf courses. Can you say "aquifer overdraft"?

 Phil Ngai +1 408 749 5720
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