Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!ncar!midway!msuinfo!rang From: rang@cs.wisc.edu (Anton Rang) Newsgroups: comp.sys.mac.programmer Subject: Re: System 7.0/Supervisor Mode ? Message-ID: Date: 16 May 91 04:36:48 GMT References: <10972.282FE0AB@stjhmc.fidonet.org> <1991May15.024320.9727@world.std.com> Sender: news@msuinfo.cl.msu.edu Organization: UW-Madison CS department Lines: 19 In-Reply-To: siegel@world.std.com's message of 15 May 91 02:43:20 GMT In article <1991May15.024320.9727@world.std.com> siegel@world.std.com (Rich Siegel) writes: [ about running in user mode ] > It's trivial to do, since it only involves changin a single bit >in the status register, and it'll only break software that depends on >exception stack frames Well, actually it's a little messier, since you have to make sure that the user and supervisor stack frames are aligned at trap and interrupt time, and you need to interpret the "MOVE SR" and other privileged instructions that some software uses, but it's not hard. > , but it's a completely useless thing to do on >a Mac SE, which is neither pre-emptive nor is it capable of supporting >an MMU directly. Yeah, I agree completely. :-) Anton +---------------------------+------------------+-------------+----------------+ | Anton Rang (grad student) | rang@cs.wisc.edu | UW--Madison | "VMS Forever!" | +---------------------------+------------------+-------------+----------------+