Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site brl-tgr.ARPA Path: utzoo!watmath!clyde!bonnie!akgua!sdcsvax!dcdwest!ittvax!decvax!genrad!panda!talcott!harvard!seismo!brl-tgr!tgr!ron@BRL-TGR From: Ron NatalieNewsgroups: net.unix-wizards Subject: Re: How is \"single-user\" done? Message-ID: <8232@brl-tgr.ARPA> Date: Mon, 11-Feb-85 13:01:25 EST Article-I.D.: brl-tgr.8232 Posted: Mon Feb 11 13:01:25 1985 Date-Received: Thu, 14-Feb-85 02:55:30 EST Sender: news@brl-tgr.ARPA Organization: Ballistic Research Lab Lines: 24 > It means that it cannot process several jobs at once. Granted, the > IBM PC has the ability to run several *processes* belonging to the same user, > the capability of context switching with regard to several users is a bit > trickier. Wrong, the difficult in doing context switching is the same under UNIX irregardless of the uid's of the processes being run. > The CPU does not have the capability to block illegal memory > accesses (PAGING/VM), nor the speed required for multi-user. PAGING/VM is not required, just simple memory protection. The lack of memory protection alone is not the reason for the PC being a single user machine. Protecting one users task from trashing the memory of another of his, or writing on the operating system's memory is just as important as keeping him from stomping on other users. The real reason the IBM-PC is a single user machine is that no one in his right mind would consider it otherwise. First, as you stated before, it is slow. Second, the first user gets to use the CPU display and keyboard, everyone else is a second class citizen when they use the serial ports. IBM-PC software developers end of developing all their software to run assuming your using the console, since it is the easy way out and is the only terminal on the system in 99.9% of the cases.