Path: utzoo!attcan!uunet!samsung!usc!wuarchive!hsdndev!spdcc!iecc!johnl
From: johnl@iecc.cambridge.ma.us (John R. Levine)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: QEMM slows down floating point!?!?
Message-ID: <1990Dec11.145038.12228@iecc.cambridge.ma.us>
Date: 11 Dec 90 14:50:38 GMT
References: <3599@ryn.mro4.dec.com>
Distribution: comp
Organization: I.E.C.C.
Lines: 18

In article <3599@ryn.mro4.dec.com> reisert@ricks.enet.dec.com (Jim Reisert) writes:
>QEMM puts the processor in protected mode.  In this mode, interrupts slow
>down.

Quite true.

>FP coprocessor uses interrupts to signal when results are ready.
>Hence the slowdown.

Not true at all, there's a dedicated READY line.  But you're close.  The
original question was about a machine with no 387, and the usual way to
emulate a 387 is to trap all of the floating point instructions and simulate
them.  Since the traps are slower, the emulation is slower.

-- 
John R. Levine, IECC, POB 349, Cambridge MA 02238, +1 617 864 9650
johnl@iecc.cambridge.ma.us, {ima|spdcc|world}!iecc!johnl
"Typically supercomputers use a single microprocessor." -Boston Globe