Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rochester!kodak!elmgate!jdg From: jdg@elmgate.UUCP (Jeff Gortatowsky) Newsgroups: comp.sys.m68k Subject: Re: move sr/move ccr: crock Message-ID: <561@elmgate.UUCP> Date: Sat, 24-Jan-87 16:58:09 EST Article-I.D.: elmgate.561 Posted: Sat Jan 24 16:58:09 1987 Date-Received: Sun, 25-Jan-87 20:39:03 EST References: <809@imagen.UUCP> Reply-To: jdg@aurora.UUCP (Jeff Gortatowsky) Followup-To: comp.sys.m68k Organization: Eastman Kodak Company, Rochester, NY Lines: 20 Keywords: logic? CCR Protection Summary: Can you say 'virtual machine'? Sure ya can. My understanding of the Move From STATUS reg difference on the 68k vs. the 010 and 020 is that this one simple difference allows the implementation of virtual machines. This is where each process thinks it has it's OWN operating system that is running in supervisor mode but indeed is just another task under some other master executive. If you were allowed to 'see' the status register you'd find out that your so called operating system is really not in supervisor mode, something a virtual machine concept does not tolerate. Instead, the REAL master operating system traps the move status register instruction and gives your fake operating system the impression it's in supervisor mode by setting the S/U bit in the copy it returns. I hope I haven't explained this too poorly. I'm not an OS expert but this is what Motorola told me in an 020 training class. -- Jeff Gortatowsky {allegra,seismo}!rochester!kodak!elmgate!jdg Eastman Kodak Company