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From: bcw@rti.UUCP (Bruce Wright)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Dumpster diving pays off (sorta)
Summary: Hard disk / Video cards
Message-ID: <3603@rti.UUCP>
Date: 23 Feb 90 05:42:28 GMT
References: <19768@nuchat.UUCP> <6550@cps3xx.UUCP>
Organization: Research Triangle Institute, RTP, NC
Lines: 59

In article <6550@cps3xx.UUCP>, usenet@cps3xx.UUCP (Usenet file owner) writes:
> In article <19768@nuchat.UUCP> seven@nuchat.UUCP (David Paulsen) writes:
> >
> >I recently rescued an ancient IBM-PC from the dumpster.. and it works!
> >
> >My question: what exactly do I have to do to this beast to install a
> >harddrive?
> 
> I don't believe you can do too much in the way of a hard disk, at least
> not a full or half height drive. There may be a possibility that you can
> upgrade the bios. I'm not familiar with hard cards, but my impression is
> that they need to be supported by the bios the same as regular hard
> disks.
> 
> According to <begin underline>The Winn Rosch Hardware Bible<end
> underline> (how do you underline anyway?) the original IBM PC introduced
> in 1981 cannot handle advanced video adaptors (presumeably EGA) or hard
> disks.

There is a direct connection.  One problem with the old original
PC BIOS was that there was no provision for BIOS extension ROMs.
This mechanism is used by essentially all hard disk controllers
(This is code that usually winds up at location C800:0).  It is
also used by the EGA, PGA, and VGA video adapters (this is code
that usually winds up at location C000:0).  The BIOS extensions
have a special prefix code (55AA) to allow the regular BIOS to
recognize them.

Hard cards run into exactly the same problems.  The controller
bootstrap code has to live somewhere.

There should be no particular problem finding replacement BIOS 
chips, if you aren't sold on getting a genuine IBM BIOS chip.
That would probably be pretty hard to find at this late date,
original PC is so dated.

There is an alternative.  It is possible to boot such a machine
from floppy and then switch over to the hard drive to do all 
the "real" work.  You would either need a disk driver on the
floppy, or a special program to tie the hard disk bIOS into the
BIOS transfer vector (I don't think this is done automatically
by the low-level MS-DOS code on such an old machine ... that's
usually the function of the ROM-BIOS, as noted above).  You
would probably want to redefine COMSPEC, for example, to point
to COMMAND.COM on the hard disk drive.  It does get to be a bit 
of a pain though to have to hunt up the boot floppy all the 
time (since you will want to use the floppy drive(s) for other 
disks too, you can't keep the boot disk in the drive _all_ the 
time ...).  If you are willing to do enough groveling it is 
probably possible to do a similar trick with an EGA/VGA video 
adapter, with a special program in the AUTOEXEC.BAT file on 
the boot floppy to link the BIOS extension code into the low 
memory transfer vector for the BIOS.

If you are stuck with the old BIOS, and have _any_ cash to spare,
you would be doing yourself a big favor to upgrade to a modern
BIOS.  Replacement chips only cost a few bucks.

						Bruce C. Wright