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From: madd@bucsb.bu.edu.UUCP
Newsgroups: comp.lang.c
Subject: Re: Fork and Exec
Message-ID: <889@bucsb.bu.edu.UUCP>
Date: Wed, 1-Apr-87 22:40:25 EST
Article-I.D.: bucsb.889
Posted: Wed Apr  1 22:40:25 1987
Date-Received: Sat, 4-Apr-87 10:27:19 EST
References: <6635@brl-adm.ARPA>
Reply-To: madd@bucsb.bu.edu.UUCP (Jim "Jack" Frost)
Organization: ODO (Organization for the Disorganization of Organization)
Lines: 31

In article <6635@brl-adm.ARPA> bagpiper@csvax.caltech.edu writes:
>   What is the difference between fork and exec in a unix environment and
>   furthermore how does that map into a MS-Dos environment??

No problem.  fork() causes program execution to split into two
identical processes.  They have independent data sections (although the
two are identical to begin with) and may have shared code, although on
some systems it is easier to duplicate the code than to share it.

exec() is slightly different.  It means to load in a new program ON
TOP OF the current one.  Thus to run a program and return, you would
fork(), then have the child process of the fork perform an exec().
When the new program exits, the program that executed the fork() will
be notified.  Usually this parent sits in a wait state, although not
always.

MS-DOS is a bit different.  Because it's not multitasking, the concept
of fork() is impossible.  Instead, there exists an exec function that
performs the functions of ALL THREE of the unix functions fork(),
exec() and wait().  When you call exec, MS-DOS loads the new program
into a new space, and gives it control.  When it terminates, control
is returned to the parent process.  This is much more primitive than
in unix.

I hope this is helpful.

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          Jim Frost * The Madd Hacker | UUCP: ..!harvard!bu-cs!bucsb!madd
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