Path: utzoo!mnetor!uunet!husc6!bu-cs!bzs
From: bzs@bu-cs.BU.EDU (Barry Shein)
Newsgroups: comp.arch
Subject: Re: More than 32 bits needed where?
Message-ID: <20022@bu-cs.BU.EDU>
Date: 20 Feb 88 00:31:51 GMT
References: <9495@steinmetz.steinmetz.UUCP> <3815@megaron.arizona.edu> <15781@beta.UUCP>
Organization: Boston U. Comp. Sci.
Lines: 46
In-reply-to: jxdl@beta.UUCP's message of 19 Feb 88 17:00:03 GMT



From: jxdl@beta.UUCP (Jerry DeLapp)
>Address space is like disk space is like memory is like money. You can
>always use up everything you have and then some.

Actually I've always felt that this belief was untrue. It's more like
the amount of memory or disk space is a function of the speed of
accessing it and using it. What use would 1GB of main memory be on a
Vax750 for example? Just zeroing it would probably take about 20
minutes (one 4 byte word per loop, 4 instruction times per loop, about
1000 seconds, cut it in half if you like, it doesn't change the
argument), let alone actually making much use of it in real
calculations.

NOTE: This is not to say that *no* one can make use of massive memory,
but the applications diminish as the memory grows, and what
constitutes "massive" memory is dependant upon other elements of a
system (1GB on a Cray-2 is modest if not limiting.) The real point is
that there are economic trade-offs and there is definitely a point
where you'd be better off spending your money on a faster CPU
(assuming finite money) than more memory. A "truism" like the above
is actually not quite true.

What you really want is to find some sort of balance. Given the past
history of computing it's not surprising to hear people say there is
no limit to the need for more memory (although I will say that the
poster's address at Los Alamos Natl Lab might indicate a special case
environment.)

I actually think this is more important a comment than it might at
first seem and even applies to mere CPU speed which eventually gets
out of balance with the software for all but the most exotic
applications (how many people out there would throw away their current
workstation and pay for a new one merely to double its CPU speed? How
many would rather spend the same money on some software to make their
work easier (assuming finite funds)?)

See, the world is changing for a lot of folks, it's an important
change.  Granted these choices have always existed, but I do think the
threshold is moving rapidly, there are limits to human reaction time.

	-Barry Shein, Boston University

P.S. I know I've been thru this before in the past, it's kinda like
when I teach a class and get this urge on the first day to say "didn't
I explain this last* year?!"