Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!utah-gr!stride!mitch From: mitch@Stride.COM (Thomas Mitchell) Newsgroups: comp.unix.questions Subject: Re: Is UNIX(TM) Multi-User? Summary: Yes I think so yet... Message-ID: <850@stride.Stride.COM> Date: 26 Aug 88 22:27:49 GMT References: <880@taux01.UUCP> <213@bhjat.UUCP> <1640@uop.edu> <404@cpro.UUCP> <15287@shemp.CS <365@pigs.UUCP> <11945@steinmetz.ge.com> <4871@netnews.upenn.edu> Reply-To: mitch@stride.stride.com.UUCP (Thomas Mitchell) Organization: MicroSage, 680 S. Rock Blvd, Reno, NV 89502 Lines: 60 >| | is unix REALLY a multi-user operating system? ... because it is a multi-tasking o/s? Yes, not because it is multi-tasking but because of ownership. >| Any multitasking o/s can be a multiuser system, provided that the user >| agent (shell or whatever) is a normal process. No must have ownership or all tasks look the same. Without ownership it is only multi-tasking. Well -- multitasking and multiuser. Each person has a differing concept about multi everything (user, tasking, processor). In a multiuser OS there should be the concept of ownership. However, the hooks of ownership need not be available to the user. A multiuser OS also need not be multitasking. As I thought about all the permutations it became useful to write them down. Start with a single user OS. (loader) Then a multitasking single user OS. (multi-loader) Then move to a virtual operating system which permits any user to believe that he is the only user on the machine. The OS imposes virtual (solid) walls between one user and another. If this is a multi user environment we may have multiple users on different terminals. No user can see, feel or in any way learn about the other. When one user is 'idle' the OS places an idle loop in his time slice so even a stop watch cannot see the other user. The simplest of this type of virtual environment would permit the user a single task. Up scale from this each user could have the option of multiple processes (tasks). Down scale, only one of many could be active at any time. Say the machine has one console. When I sit down and login there is no clue that you were there yesterday. Then begin to provide tools to share resources. Visible ownership advisory Visible ownership enforced Invisible ownership enforced Resource locking advisory Resource locking enforced Quotas (processor, disk, I/O, printer paper) Communication Services -- virtual users (lpr) --------------------------------------------------------------------------- Unix is not the OS of the future. It is the environment the OS of the future will be written in. -- Thomas P. Mitchell (mitch@stride1.Stride.COM) Phone: (702)322-6868 TWX: 910-395-6073 FAX: (702)322-7975 MicroSage Computer Systems Inc. Opinions expressed are probably mine.