Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uwm.edu!ux1.cso.uiuc.edu!csrd.uiuc.edu!s4.csrd.uiuc.edu!bruner From: bruner@sp15.csrd.uiuc.edu (John Bruner) Newsgroups: comp.sys.mac.hardware Subject: Re: System 7.0 and RAM Message-ID: Date: 25 Apr 91 18:09:20 GMT References: <1991Apr11.193950.7332@cbnewsk.att.com> <1991Apr12.201532.18426@visix.com> <97@eclectic.COM> <1991Apr22.042204.1291@lynx.CS.ORST.EDU> Sender: news@csrd.uiuc.edu (news) Distribution: usa Organization: CSRD, University of Illinois Lines: 23 In-Reply-To: aland@chaos.cs.brandeis.edu's message of 24 Apr 91 15:57:28 GMT In article aland@chaos.cs.brandeis.edu (Alan D.) writes: > In article <1991Apr22.042204.1291@lynx.CS.ORST.EDU> hasses@prism.cs.orst.edu (Stephen Haase) writes: > >> One VERY annoying thing I noticed with system 7's virtual memory was that x >> amount of HD space does not equal x amount of extra RAM.... > > Very annoying, but quite necessary. You need to have some place to > swap OUT the memory you're replacing with the new memory... And > therefore you need as much free space on the HD as you want in virtual > memory, notwithstanding the amount of actual RAM you have. Sadly, it isn't necessary; rather, it simply is easier to implement virtual memory by associating a fixed secondary storage address for each virtual page. Dynamically assigning secondary storage addresses as pages are paged out does incur some additional space overhead, but the space savings are worth the extra bookkeeping. Many BSD-derived UNIX implementations take this approach, but there are certainly implementations that do not. It is too bad that Apple did. It does, however, encourage users to buy more disc storage. -- John Bruner Center for Supercomputing R&D, University of Illinois bruner@csrd.uiuc.edu (217) 244-4476