Re: PC20-III

From: Sami Rautiainen (
Date: 2001-04-17 20:43:33

On Tue, 17 Apr 2001, Christopher A Bongaarts wrote:

> As Bryan Pope once put it so eloquently:
> [Someone else said:]
> > > Some centuries ago there existed PC's which had a BIOS which didn't know of
> > > the existance of harddisk at all. Then came the AT with some preprogrammed
> > > types. The one you mean is type 4: 620 tracks, 4 heads, 17 sectors. Those
> One of the "features" of the XT over the original PC was the addition
> of hard disk support to the BIOS.

Yep. PC/XT had 10MB MFM hard drive in the basic configuration, while
original PC didn't - for PC there was an awfully expensive IBM add-on
controller with its own BIOS.

> (To another someone else: all PC's have BIOS, but not all have the SETUP
> program in ROM.)

(Original PC didn't have setup program at all, since it had no CMOS. Later
disk based setup programs were quite common, before 386's.)

> > But I do remember using SETUP from a floppy.  But I always thought what a 
> > *bad* idea it was to setup your computer with a disk.  Unless that disk was 
> > nailed to the computer, the next time you wanted to change something you 
> > would have to spend have the day looking for the floppy to do a change that 
> > would only take five minutes.
> On the upside, the layout of the CMOS RAM area is pretty standard, so
> a "generic" SETUP program should be able to do simple setup on most
> PC's, or you could write your own without too much effort.  I think
> the basic 46 or so HD types are also reasonably standardized (from the 
> AT on, anyway).

Only the first 15 are "standard" (=defined by IBM at XT technical
reference), rest are usually different from vendor to another, especially
with compatibles made by Compaq, HP, Wyse and others. "Nameless" clones
basically used only few different BIOS vendors at the time (Phoenix and
later AMI), and there those types are more constant. But still, two clones
with Phoenix BIOSes may have different set of hard drive types.

> But as noted elsewhere, the specific problem here appears to be 8 bit
> vs. 16 bit IDE interfaces on the Commodore PC's.

Yep. Further Commodore's BIOS is very picky about hard drives. If the
physical layout does not match the one set in BIOS, problems will appear
for sure.

IMHO easiest way to add more hard drive space to Commodore's PC, is to use
original one as the boot drive and add an additional (secondary)
controller. Additional controller can be accessed with a DOS driver if it
does not have its own BIOS. One pretty good DOS IDE driver for old
machines has been available from Quantum in the past.

If the original drive cannot be used, well, then there is a problem since
8-bit IDE drives can be difficult to find and as far as I can remember,
the controller at the motherboard cannot be easilly disabled. An
additional controller with its own BIOS may work in this case.

  Sami Rautiainen                                      .. who made who?

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