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From: dave@uwvax.UUCP (Dave Cohrs)
Newsgroups: net.unix
Subject: Re: Compatibility mode for VAX 4.2 BSD
Message-ID: <203@uwvax.UUCP>
Date: Sun, 26-May-85 14:20:00 EDT
Article-I.D.: uwvax.203
Posted: Sun May 26 14:20:00 1985
Date-Received: Mon, 27-May-85 08:00:59 EDT
References: <456@leadsv.UUCP>
Distribution: na
Organization: U of Wisconsin CS Dept
Lines: 29

>    1) Is it possible to use compatibilty mode on a VAX without severely
>       hampering other users? I thought that compatibility mode was system-
>       wide (ie. everybody is running in compatibility mode) and that is
>       unacceptable.

No.  When you run in compatability mode, all compatability-mode system calls
cause 5 context switches instead of 2 as the system calls are emulated by
the compat (often called v7run) program.  If a number of people are using
the compat programs at the same time, your system will bog down.  The
system-wide compatability is 4.1 compatability which is not necessary to
use Pdp-11 compatability.

>    2) What is compat and where can I get it and does it run on 4.2BSD?

You should find the source in /usr/src/games/compat.  Note that there are
a couple bugs in this code which cause SIGILL to be handled incorrectly.

>    3) If I am using compat, what does it look like (maybe a PDP-11 running
>       4.2BSD)?

V7run (compat) emulates version 7 execution.  2.8 and 2.9 executables also
work, at least they do for system calls that are also on version 7.

-- 
dave cohrs
...!{allegra,harvard,ihnp4,seismo}!uwvax!dave
dave@wisc-limburger.arpa

    (bug?  what bug?  that's a feature!)