Path: utzoo!utgpu!watserv1!watmath!uunet!shelby!apple!vsi1!teraida!ditka!kls
From: kls@ditka.UUCP (Karl Swartz)
Newsgroups: unix-pc.general
Subject: Re: Fix disks: More than 2 drives?
Message-ID: <20103@ditka.UUCP>
Date: 2 Feb 90 10:37:27 GMT
References: <1990Feb1.070641.17593@stb.uucp>
Reply-To: kls@ditka.UUCP (Karl Swartz)
Organization: Inaction Central, San Jose, California
Lines: 35

In article <1990Feb1.070641.17593@stb.uucp> michael@stb.uucp (Michael Gersten) writes:
>Here's a simple question: Did the fix disk hard disk driver allow
>using 4 drives (since there is hardware out there that supports it)?

Here's the simple answer: No.

Elaboration: According to what I was told by someone who knows the
code quite well, it won't ever happen, nor will double floppy drives
happen.  Not with a few binary hacks to the drivers, not with a few
days of hacking on the source.  Nothing short of a complete rewrite
of the disk drivers (hard and floppy) would increase the limit above
the present one floppy and two hard disks.

Evidently, there are various places where the drive select is stored
as a two-bit field, where one bit selects hard or floppy.  Alas, the
floppy driver hasn't even a hint of a clue about drive selects so
the bit available for selecting between two floppies is wasted.  At
one point there was thought that it might be stolen for a third hard
drive but it quickly became obvious that that would lead to a major
project too.

Of course one might increase the field to three bits, giving four
ways to select the one floppy plus four hard drive selects, but the
code evidently isn't well parameterized, and would be quite dicey
not to mention difficult to modify in this manner.

So, while John Milton's efforts to support two floppies and four
hard disks in his hardware are admirable, they are wasted, unless
somebody comes up with a new OS for the UNIX PC.

-- 
Karl Swartz			 |UUCP	uunet!apple!zygot!ditka!kls
1-408/223-1308			 |INet	zygot!ditka!kls@apple.com
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