Path: utzoo!attcan!uunet!wuarchive!uwm.edu!zaphod.mps.ohio-state.edu!mips!smsc.sony.com!dce From: dce@smsc.sony.com (David Elliott) Newsgroups: comp.sys.mac.system Subject: Re: Memory (de)fragmentation Message-ID: <1990Jun1.144817.500@smsc.sony.com> Date: 1 Jun 90 14:48:17 GMT References: <16797@phoenix.Princeton.EDU> <1990May29.145842.18701@kth.se> <4372@castle.ed.ac.uk> Reply-To: dce@Sony.COM (David Elliott) Organization: Sony Microsystems Corp. Lines: 46 In article <4372@castle.ed.ac.uk> nick@lfcs.ed.ac.uk (Nick Rothwell) writes: >This implies that VM makes the whole handles business obselete (yes?) Well, I'd say that it implies that VM could make handles obsolete, but it is my understanding that System 7's use of VM can't. In a "virtual machine" type of VM (a la BSD Unix), every process has (or can have) the same starting address and can have basically the same address space. Thus, each process more or less "owns" the entire machine while it is running, and VM is used to make this possible. As a result, something like MacOS handles isn't really needed in general (though this doesn't mean that the concept is totally alien, as people familiar with vi and most Unix compilers can see). My understanding of MacOS VM is that it allows the machine to appear as though it has up to 14MB of total RAM by backing real memory with disk space. A system with 8MB of RAM won't even use VM until more than 8MB of memory is being used (I would like to be proved wrong on this). For applications running under MultiFinder, this won't mean that their SIZE resources will be ignored. You will be able to run more applications, but they will still have to run in the requested area of memory. Sadly, this does you little good if you tend to keep few processes running because of memory protection problems (I hardly ever run out of memory on my 8MB system because of this). I would assume, though I've never heard this said, that the biggest improvement would be in the system heap, which is already dynamically sized. Even if Apple were to modify MacOS so that each process lived within a virtual machine environment, handles are still very useful, as they make it possible to deal with seldom-used resources in a very nice way. Why waste VM on a resource that you won't be using? Without adding some kind of disk buffer cacheing, handles are still the only game in town. In any case, I would suspect that handles will become unused by the OS long before there are system trap calls that don't use them. -- David Elliott dce@smsc.sony.com | ...!{uunet,mips}!sonyusa!dce (408)944-4073 "If I had a hat the size of Oklahoma, I'd be a happy person."