Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rochester!ur-tut!tuba From: tuba@ur-tut.UUCP (Jon Krueger) Newsgroups: net.arch Subject: Re: Very large memories Message-ID: <719@ur-tut.UUCP> Date: Tue, 23-Sep-86 10:18:48 EDT Article-I.D.: ur-tut.719 Posted: Tue Sep 23 10:18:48 1986 Date-Received: Tue, 23-Sep-86 22:15:14 EDT References: <1164@ncr-sd.UUCP> <2383@peora.UUCP> <683@ur-tut.UUCP> <2449@peora.UUCP> Reply-To: tuba@ur-tut.UUCP (Jon Krueger) Organization: Univ. of Rochester Computing Center Lines: 63 > Joel Upchurch @ CONCURRENT Computer Corporation (A Perkin-Elmer Company) joel@peora.UUCP writes: > I don't agree that applications are growing faster than > memory is getting cheaper. I might agree that the applications > are growing faster than the amount of memory usually installed > in most computers. > Back in 78 it cost me $200 dollars to add 16KB to my Apple II. > Last month I paid $401 to put 2 more megabytes in PC clone. An alternate way of expressing the trend is that over the last eight years, memory costs have halved every 1 to 2 years. Bell's law states that applications grow at the rate of an address bit every two to three years. Therefore, accepting your figures as accurate, I stand corrected. The semiconductor industry has created ever cheaper memory products, and more than kept up with demand, over the last eight years. Too bad they haven't increased the address bits of their processors at the same rate. > The cost of disk storage hasn't gone down nearly as fast as > the cost of memory. Especially the kind of high performance > drives that make good paging devices. You can have virtual > memory without fast disks, but then you need more memory > to maintain equivalent performance levels. If your applications are i/o bound by paging, buy more memory. Tuning your application on a virtual memory machine gets you more performance out of less memory, not adequate performance out of inadequate memory. > I will agree that for any given memory N, there will always > be applications that won't run in N. But as time goes on these > applications will more and more be oddballs, rather than the > mainstream. There will niche computers to run them, but the > common run of applications won't need this kind of support. About the turn of the century, there was a serious proposal to close the Patent Office, since everything useful had already been invented. Let's not limit tomorrow's application size in today's architectures. I don't pretend to predict tomorrow's applications. But it's a safer bet that they'll require more memory than to set an upper limit on typical demands. Bell's Law has surprising generality and longevity. > This is not to say that future processors won't support > virtual memory. Address translation/ memory protection > support is useful on any multitasking system, with or > without virtual memory and the incremental cost for > hardware to generate page faults isn't much. A lot > of people seem to be excited about the 80386, but not > because of virtual memory, but because of better support > for multitasking. Neither. Imagine the technical excitement of the 80386 if the IBM PC market didn't exist, had never existed. Yawn. Just another pretty chip. --> Jon Krueger uucp: {seismo, allegra, decvax, cmcl2, topaz, harvard}!rochester!ur-tut!tuba Phone: (716) 275-2811 work, 235-1495 home BITNET: TUBA@UORDBV USMAIL: Taylor Hall, University of Rochester, Rochester NY 14627 -- --> Jon Krueger uucp: {seismo, allegra, decvax, cmcl2, topaz, harvard}!rochester!ur-tut!tuba Phone: (716) 275-2811 work, 235-1495 home BITNET: TUBA@UORDBV USMAIL: Taylor Hall, University of Rochester, Rochester NY 14627