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From: rmtodd@uokmax.UUCP
Newsgroups: comp.os.minix
Subject: Re: Which clones *don't* run MINIX
Message-ID: <447@uokmax.UUCP>
Date: Sat, 7-Feb-87 23:14:23 EST
Article-I.D.: uokmax.447
Posted: Sat Feb  7 23:14:23 1987
Date-Received: Mon, 9-Feb-87 01:43:24 EST
References: <275@ihnp3.UUCP> <459@moncol.UUCP> <2529@well.UUCP>
Organization: University of Oklahoma, Norman, OK
Lines: 34
Keywords: MINIX BIOS COMPATIBILITY
Summary: BIOS isn't reentrant

In article <2529@well.UUCP>, hrh@well.UUCP (Harry Henderson) writes:
> My apologies if this is a dumb question, by why the design decision to
> make MINIX so hardware-dependant. Why wasn't the BIOS used? Does the
> BIOS not provide enough functionality? If the problem is just speed,
> why not write a slower version for those of us whose chips don't have
> the right pedigree? The hardware dependance strikes at one of the
> basic tentents of UNIX philosophy.
  It's not a dumb question.
  The problem is that the people who wrote the ROM BIOSes for the clone
motherboards, the HD controllers, etc. did not write them with multitasking
in mind.  Thus the BIOS code is not reentrant -- multiple tasks cannot
call the BIOS without mass confusion arising as task 2's call writes on top
of the variables set by task 1's call.
  You could try to set it up so that only one task at a time can access the
BIOS and all the rest block.  Wendin's PCUNIX does this.  In fact, if I
remember correctly, they found that you couldn't even safely switch out of
the current task if it was executing BIOS code.  It does rather interesting
things to the system performance.
  For these reasons, if you want really good multitasking performance, don't
use the ROM BIOS.  I've heard that PC/IX, like MINIX, is picky about what
hard drives it'll use for the same reason.  I suspect XENIX acts the same
way.
  On a (somewhat related) subject, does anyone know just what *is* the type
of controller MINIX expects?  A check inside my machine shows Western
Digital chips (WD1010, WD1015, and WD1020, I think), and a ROM HD BIOS with
"Copyright (c) 1985 Western Digital".  I'd like to know if this is the kind
that works.
  As for violating "the tenets of the UNIX philosophy", all UNIX systems
have device-dependent driver code.  The UNIX philosophy just puts all the
mess in a small section of the code, leaving the rest relatively portable.
--------------------------------------------------------------------------
Richard Todd
USSnail:820 Annie Court,Norman OK 73069
UUCP: {allegra!cbosgd|ihnp4}!okstate!uokmax!rmtodd