Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!gem.mps.ohio-state.edu!apple!chuq From: chuq@Apple.COM (Chuq Von Rospach) Newsgroups: comp.sys.mac Subject: Re: PMMU... Message-ID: <35041@apple.Apple.COM> Date: 26 Sep 89 22:30:10 GMT References: <32679@srcsip.UUCP> Distribution: usa Organization: Life is just a Fantasy novel played for keeps Lines: 41 >> Unfortunately, none of this excellent memory management hardware >>does you any good unless you run A/UX. The regular Mac operating system >>just turns any memory management unit off and runs in "real mode". Unless you buy the Virtual INIT. >>Even >>release 7, much to the disappointment of people who don't like system >>crashes, doesn't use the MMU. Not true. System 7 will use the MMU to implement virtual memory. As has been mentioned about 4,000,000 times on c.s.m in the last few months. >>On a machine with memory management and >>a solid operating system, an application can't crash the system no matter >>what it does. Essentially all workstation-class machines (Suns, Apollos, Um, that's a nice theoretical ideal, but I spent enough time at Sun crashing machines to know that applications *can* crash the system, even when they're not supposed to be able to. >Sorry dude, you almost got it but not quite. System 7 implements virtual >memory which REQUIRES a PMMU (either the 030's own or the 851 for the 020). Just to make sure it's clear. System 7 does not require a PMMU. To use virtual memory with System 7 does. (there's enough confusion on that point that it needs to be reiterated) >What System 7 does not implement is protected memory where the MMU is used >to prevent code in one address space from writing directly to another >address space. As I said above, even *with* protected memory applications can do all sorts of nasty things. They aren't supposed to be able to, but sometimes they do anyway. (those are called bugs, of course....) -- Chuq Von Rospach <+> Editor,OtherRealms <+> Member SFWA/ASFA chuq@apple.com <+> CI$: 73317,635 <+> [This is myself speaking. I am not Appl Segmentation Fault. Core dumped.