Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!think.com!mintaka!mole.gnu.ai.mit.edu!dbert From: dbert@mole.gnu.ai.mit.edu (Douglas Siebert) Newsgroups: comp.sys.mac.system Subject: Re: Virtual Memory and Sys 7 Message-ID: <1991May9.162601.19210@mintaka.lcs.mit.edu> Date: 9 May 91 16:26:01 GMT References: <1991May8.143042.20137@bigsur.uucp> <1991May9.042425.598@gla-aux.uucp> Sender: news@mintaka.lcs.mit.edu Organization: The Internet Lines: 53 In article <1991May9.042425.598@gla-aux.uucp> glenn@gla-aux.uucp (Glenn L. Austin) writes: >webster@bnr.ca (Brent Webster) writes: >>Just a few comments on Apple's version of virtual memory. >>I have a lowly Mac II with 8Meg of ram and a 40Meg hard-drive >>running 7.0b4 OS. I been running a Smalltalk-80 application on >>my SparcStation whose image size is about 6.5 Megs and I wanted to >>try running it on my Mac (speed initially is not a concern). > >>I went to reconfigure my memory via the Memory control panel but it >>only allowed me to increase the memory to 11 Megs. When I rebooted my >>Mac, to my astonishment, my harddisk was short 11Megs and not the >>3Megs plus some overhead which I expected. I can live with that >>but I am wishing for a more elegant solution. > >This is so that the entire memory map is available. If only the additional >RAM was allocated, where would you put the current RAM so that you could >swap in the additional RAM? There would always be some overhead, and by >allocating the full memory size, you remove problems with double-writing, > >memory collisions, etc. I wonder how long virtual memory will remain a useful solution however. Somewhere in the Mac newsgroups in the last few days someone mentioned how the memory used by the "power" user doubles in size each year. Now considering all hubbub about older Macs being limited to 16M, I'll assume that the 1991 power user uses 16M. Take that back ten years, to 1981, and you get 16K (my Atari 800 back then had 48K so I guess I was just ahead of my time! :) ) Now I, along with 99.9% of other computer users at the time, would have laughed at the notion that in ten years 16M would be a "limitation" people are bitching about. Virtual memory provides a temporary solution, but the way things are going, I'll wager virtual memory will not be used ten years from now. Because if memory usage continues to double, we'll be running around 16G (that's 16,384M for those of you not aware what a "G" is :) ) Of course we'll have run into the 680x0's addressable limit of 4G by then, but many of us will have migrated to 64-bit processors by then. Anyway, if we have even 2G of physical RAM by then (a conservative estimate I'd bet) we'll need to allocate several GIGS of memory on our harddisks to act as virtual memory. Now even if hard disk technology has progressed as well as it has in the past 10 years (from 10M winchesters to 1G Fujitsus) I'd hate to think how *slow* things would be, if we try to use much of that virtual memory. Of course we'll probably all be using IBM's SHRAM chips arrayed to give us gig after gig of "removal RAM" by then anyway....:) -- Doug Siebert | dbert@gnu.ai.mit.edu MBA Student (2nd year) | "All opinions expressed herein are obviously (starting MS in CS this fall?) | superior to yours or you wouldn't have need The University of Iowa | to be reading this, now would you?" :-)