Xref: utzoo comp.os.misc:622 comp.os.cpm:1817
Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!pyrnj!pyrdc!uunet!mcvax!unido!fauern!faui44!mlelstv
From: mlelstv@faui44.informatik.uni-erlangen.de (Michael van Elst )
Newsgroups: comp.os.misc,comp.os.cpm
Subject: Re: a very naive Question???
Message-ID: <685@faui44.informatik.uni-erlangen.de>
Date: 17 Oct 88 13:27:01 GMT
References: <6693@ut-emx.UUCP>
Reply-To: mlelstv@faui44.UUCP (Michael van Elst (kdebugger))
Organization: CSD., University of Erlangen, W - Germany
Lines: 31

In article <6693@ut-emx.UUCP> kannan@emx.UUCP or nataraj@happy.cc.utexas.edu writes:
>    I read an article in UNIX World comparing system V and AIX.
>     It clearly stated that System V did not have VM(Virtual Memory concept).
Of course, System V _uses_ virtual memory.
>
>   (1) If there is no VM, how does the operating system, bring the programs
>    from secondary storage to main for execution.(System V )
I don't see the point. VM is used to run large (or multiple) programs
in a limited real memory. The secondary storage is problem of the
file system. You load programs from a code-file, that contains
the code and data segments and some other useful information like
stacksize.
>
>   (2) How does MS-Dos solve the above problem?
MS-DOS has no VM. It runs all programs in a single address space for
there is only one process. Loading of programs is ... (see answer to 1)
>    
>    (3) I have comments like Unix needs at least 4M of main memory?
>      Is it for all the daemons to run?
No. UNIX is rather large operating system. The kernel is some 100kbytes
large and you need buffer space to speed up disk i/o.
You need approx. 1.5M to 2M for a single user workstation and 1M for
each other user. So 4M is an average size for an UNIX machine but not
required.
The deamons are programs that handle regular system activities like
printer spooling. For UNIX handles virtual memory, those processes
are swapped out on disk and don't need real memory unless they
really DO anything useful.
				Michael van Elst

E-mail: UUCP: ...uunet!unido!fauern!faui44!mlelstv