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From: cdshaw@alberta.UUCP (Chris Shaw)
Newsgroups: net.arch
Subject: Re: VERY LARGE main memories
Message-ID: <81@alberta.UUCP>
Date: Thu, 25-Sep-86 02:40:11 EDT
Article-I.D.: alberta.81
Posted: Thu Sep 25 02:40:11 1986
Date-Received: Fri, 26-Sep-86 21:03:20 EDT
References: <7832@lanl.ARPA>
Reply-To: cdshaw@pembina.UUCP (Chris Shaw)
Organization: U. of Alberta, Edmonton, AB
Lines: 41

In article <7832@lanl.ARPA> jlg@a.UUCP (Jim Giles) writes:
>So the bottom line is: we still don't have complete control, we still
>need to do a lot of work on our own, and we still have a slower memory
>interface than necessary.
>

..and we still don't have any numbers to back up this or any other position.

Basically, Jim's argument has been "our machines are too big, the users love
performance, and they do weird things, so VM is no go". 

The pro-VM people are saying: Use (or invent) a call to tell VM what to do, 
and thereby solve the strange usage pattern problem. This will give the 
users much more flexibility. The flexibility will come at the price of a small 
performance hit, but the performance cost is worth it. There is the added 
benefit that the cost of the system may be less, since secondary store is 
cheaper than high-speed primary store. 

I suppose the question really is, how much primary memory do you need, versus
how much can you get away with. A previous article mentioned Cray wanting
a full 16MW of primary memory. Plenty of cash mo-nee, since the memory probably
has to run fast. Is this extra cost worth it? In the infinite-wallet world
of defence research, probably not. In the "real", tight-budget world,
bang per buck matters more, and the marginal speed improvement of (say)
full-address-space core might not pan out in the face of more reasonable 
alternatives.

But then, I'm talking through my hat, too.

In any case, there are two major positions here because there are two
types of budgets to consider. Jim is in the world of "performance at any
cost", while lots of other people are into "performance at a reasonable
price".

>J. Giles
>Los Alamos


Chris Shaw    cdshaw@alberta
University of Alberta
Bogus as HELL !