Compatibility mode for VAX 4.2 BSD

[Dave Cohrs]

>    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 at wisc-limburger.arpa

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