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From: paulz@sco.COM (W. Paul Zola)
Newsgroups: comp.unix.questions
Subject: Re: Math Coprocessors
Summary: Applications, not the kernel, use the FPU
Message-ID: <12079@scorn.sco.COM>
Date: 20 Nov 90 14:46:59 GMT
References: <1990Nov12.032526.17125@mccc.uucp> <126@mq.com> <1990Nov15.184607.21575@mccc.uucp>
Sender: news@sco.COM
Reply-To: paulz (W. Paul Zola)
Organization: The Santa Cruz Operation, Inc.
Lines: 44


In article <1990Nov15.184607.21575@mccc.uucp> pjh@mccc.edu (Pete Holsberg) writes:
>In article <126@mq.com> alan@mq.com (Alan H. Mintz) writes:
>=The SCO XENIX 386 O/S definitely makes use of the FPU if it is available 
>=(according to SCO). 
>
>	Do they say in what way the OS uses it?
>	
[deleted]

There has been a great deal of confusion about this.  To put it
as clearly as possible:  the SCO XENIX *kernel* and the SCO UNIX 
*kernel* do NOT use floating-point calculations.  Since they don't
use floating-point calculations, they don't use the FPU, even if 
one is present.

What the SCO kernels do provide is a means by which application
programs can use the FPU if one is present.  The access to the FPU
is transparent to the application: applications always "see" an FPU
present, and always use the FPU instructions.  It is the kernel's 
job to hand off the FP instructions to the co-processor chip (if one
is present) or to emulate the FP instruction (if there is no FPU
present or if the kernel was instructed to ignore the FPU via the
'ignorefpu' boot string directive).

In summary:
    If an application uses floating-point instructions and an FPU
    is present, then the kernel will make sure the application 
    uses the FPU.

    If an application uses floating-point instructions and an FPU
    is not present, then the kernel will emulate the FPU on behalf
    of the application.

    In no case does the kernel itself use floating-point instructions
    or the FPU.

I hope this clarifies things for people.

-
Paul Zola			Software Support Engineer 
				paulz@sco.COM 
We only know in theory what we are doing.   - Kate Bush
    DISCLAIMER: I speak for myself, and not for SCO.