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From: bzs@bu-cs.BU.EDU (Barry Shein)
Newsgroups: net.arch
Subject: Re: Reasons For Large Main Memories
Message-ID: <1161@bu-cs.bu-cs.BU.EDU>
Date: Fri, 5-Sep-86 17:40:21 EDT
Article-I.D.: bu-cs.1161
Posted: Fri Sep  5 17:40:21 1986
Date-Received: Fri, 5-Sep-86 22:57:06 EDT
Organization: Boston U. Comp. Sci.
Lines: 43


From: rjn@duke.UUCP (R. James Nusbaum)
>Your point is also true.  However many Lisp systems are single user systems.
>Having even a couple of hundred megawords of memory could totally eliminate
>paging, as the entire system could be resident.  Take the Symbolics for
>instance.  It has a 200Mb disk used for paging and some middle amount of 
>memory (maybe 16Mb).  We have run many complex systems in this 200Mb size.
>If we had 200Mb of memory then we would have no need for paging at all!  This
>would significantly speed up many applications.

But you still miss the point. In the first place, move this to GigaBytes,
obviously adding a few more megabytes is not interesting (so why do people
keep going back to it?) Even 200MB is quite different than 5X that or
more.

Now, ok, you eliminated paging, garbage collection has become a field
service thing. But, could you do anything useful with all that memory
and that (relatively) itty-bitty processor? How long would it take you
to do a MEMQ of a list of a few HUNDRED MILLION lisp objects long?
etc.  Paging is only an advantage at some interim and relatively low
point (100-200MB perhaps, probably less.)

Now, I could see a lisp-machine type saying that only garbage
collecting on Xmas day would be a big win, if they could actually
accomplish that, and would otherwise run 'reasonable' programs.
Somehow though I suspect it won't work that way. More like the machine
down every Sunday for garbage collection (though I suppose many
long-running applications could be checkpointed to disk and a simple
re-boot would suffice.)

There might be hope here, it's more or less like using memory in
a way similar to a write-once CD, you "never" reuse scratch memory,
when you run out you put a new disk in (ie. re-boot.)

Ok, but still obviously not cost-effective (the magic ingredient that
gets thrown out whenever this topic starts getting discussed, 1GB of
memory is going to cost you around $1M [there's more than chips
involved, don't just tell me the 1MB price * 1,000, you'll need
backplane, power-supplies etc etc, if your figures come to $500K,
fine, same thing], how many of us would buy a lisp-machine to run one
application for $500-$1M? $250K?)

	-Barry Shein, Boston University