Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.arch Subject: Re: Macintosh OS Message-ID: <12539@cbmvax.commodore.com> Date: 11 Jun 90 18:13:12 GMT References: <1990May30.230248.6200@Neon.Stanford.EDU> <1935@key.COM> <30273@ut-emx.UUCP> <76700207@p.cs.uiuc.edu> <402@newave.UUCP> <1990Jun2.132847.14292@oracle.com> <26437.266ae612@vaxb.acs.unt.edu> <1682@mcrware.UUCP> Reply-To: daveh@cbmvax (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 38 In article <1682@mcrware.UUCP> jejones@mcrware.UUCP (James Jones) writes: >In article <26437.266ae612@vaxb.acs.unt.edu> ac08@vaxb.acs.unt.edu writes: >>And those preemptive multitasking systems >>suck RAM like nobody's business... >Gee, that would be news to those who have used OS-9/6809 Level One (designed >to work in a single 64K address space) for years. (Admittedly, when I composed >a mail reply (which bounced, alas), I was on a Level Two system, but even with >windowing and a 96K RAM disk, 512K is fairly comfortable.) For that matter, I >wouldn't call OS-9/68K a memory hog... In fact, a non-preemptive multitasking system, like Mac's Multifinder or MicroSoft's Windows is extremely likely to take more memory than a well designed preemptive system. The only reason the two aforementioned operating systems aren't preemptive, despite how their proponents will claim that "Cooperative multitasking is superior", is for compatibility with programs written for the the non-multitasking operating systems they replace. Such programs, and the underlying operating systems, were never designed for preemption. So they can't take a context swap anywhere, or they'll end up having some system global context information clobbered. And the reason they need more memory than a well designed preemptive system are these globals. For every context swap, all kinds of this global context information must be stored somewhere. The preemptive system need only store CPU context information -- program counter and various registers. Certainly it's possible to build a preemptive system that takes up too much memory -- UNIX System V Release 4 and OS/2 are two good examples of this. The AmigaOS will also run with the windowing system, RAM disk, etc. in 512K. Or, for that matter, 146 Megabytes (the most that can currently be plugged into an Amiga computer with existing memory cards). > James Jones -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "I have been given the freedom to do as I see fit" -REM