Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!mp.cs.niu.edu!ux1.cso.uiuc.edu!kchang From: kchang@ncsa.uiuc.edu (Kenneth Chang) Newsgroups: comp.sys.mac.hardware Subject: Re: System 7.0 and RAM Message-ID: <1991Apr25.191017.10487@ncsa.uiuc.edu> Date: 25 Apr 91 19:10:17 GMT References: <1991Apr22.042204.1291@lynx.CS.ORST.EDU> Sender: usenet@ux1.cso.uiuc.edu (News) Distribution: usa Organization: Nat'l Ctr for Supercomp App (NCSA) @ University of Illinois Lines: 25 Originator: kchang@pluto In article bruner@sp15.csrd.uiuc.edu (John Bruner) 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.... >> >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. > There's a better reason that "Apple was lazy." To quote from the manual for Connectix's Virtual (which implements virtual memory in a similar fashion): "Performance. When swapping a page in memory that has not been modified, we can speed up the page swap time by a factor of two if we can count on there still being a disk image of the unmodified page. This requires that we be able to store the image of all pages in the virtual memory space, regardless of whether it is RAM." -- Kenneth Chang | National Center for Supercomputing Applications kchang@ncsa.uiuc.edu | Consulting Office/(217)244-1144 ----------------------------------------------------------------------------- "Everything's entertainment in America eventually" -- Tracy Ullman