Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!linac!att!cbnews!cbnewsl!urban
From: urban@cbnewsl.att.com (john.urban)
Newsgroups: comp.unix.sysv386
Subject: Re: Math Co-Proc. usage
Message-ID: <1991May9.141158.6106@cbnewsl.att.com>
Date: 9 May 91 14:11:58 GMT
References: <455m21w164w@gantz.bowlgreen.oh.us>
Distribution: na
Organization: AT&T Bell Laboratories
Lines: 25

In article <455m21w164w@gantz.bowlgreen.oh.us> gantzm@gantz.bowlgreen.oh.us (gantzm) writes:
>
>        Could someone with more experience then I have, please explain
>how a math co-proc. is handled under any System V os???  What I want
>to know is, if two tasks want to use a 387 is the math unit treated
>as a resource that gets locked and unlocked?  If not is the data
>in the math co-proc. switched during a task switch, and if this is
>true isn't this slow!!!!!

Slow?  Well maybe, however, if you don't have a 387 chip, the 80387 emulator
(/etc/emulator) runs at about 2% of speed of a 387 chip.  Thus is you have
a little math intensive program that takes 35.7 seconds to run with a 80387
chip, it will take about 14 minutes with the emulator.

The 80387 (or emulator) is only locked into the processes when it is running.
When the process is swapped out, the 387 is free for the next process.  Just
like the 80386.

When the kernel changes processes, the states/registers of both the 80386 and
the 80387 are saved, so they can be restored when the original process is swapped
back in.

Sincerely,

John Urban