View Full Version : IBM PC/AT problems and questions

November 18th, 2017, 06:58 AM
Hi all, this is my first post here :)
So recently I got an IBM PC/AT from the local recycling center a few days ago and I've been trying to get it to read disks - now, mind you I have replaced the original 1.2MB FDD drive with a known tested working one. I've made several different 1.2MB boot disks that would boot from other machines but not the AT. List of disks I have done: the ATAD 2.07 disk, MSDOS 3.3, and a MSDOS 6.2 disk.
The 44MB ST-251 has also bit the dust (see here https://www.youtube.com/watch?v=neIShqU1pM4 )
Questions I want answers to: How do I use an IDE HDD with this machine? Does the PC/AT support booting off of 1.2MB diskettes?

Info about the machine: Type 1 512k board, with the rev. 2 6/10/85 BIOS, 286/8, using VGA.

Also this post error:

November 18th, 2017, 12:58 PM
I think that the AT assumes the first floppy drive is 360k until you tell it otherwise using the setup disk. You'll need to boot that first. Also I wouldn't necessarily conclude the ST251 is toast until you've told the machine it's there, again using the setup disk. 384 KB should be plenty for this purpose, if you should choose to disregard the memory fault until later.

November 18th, 2017, 01:18 PM
I've booted from a 1.2MB on a PC/AT; as long as your CMOS settings are correct (indicating a 1.2MB as A: ) you should be fine. Otherwise, the 5170 does assume a 360K if no CMOS information is available.

ISA IDE controllers are available and fairly common. Bonus points if you can get one, such as a Promise, that also contains a BIOS.

You're actually showing two errors; one with the memory and the other with the invalid CMOS setup data.

November 18th, 2017, 01:28 PM
One problem using standard IDE on an IBM PC/AT 5170, or some other early AT clones, is that the IDE drive must match one of the drive types in the BIOS drive lookup table.

There are several different solutions to this:
- Replace the IBM BIOS ROMs with third party ROMs that support entering custom drive types.
- If you have an EPROM burner, burn a replacement set of ROMs with a customized drive type table.
- Get an XT-IDE (or other IDE card that has a BIOS).
- Install an XT-IDE BIOS on a ROM card or network card. (If the motherboard has extra ROM sockets, you might be able to use those)
- Go SCSI instead :P.

November 18th, 2017, 01:38 PM
What I said about Promise IDE cards--they have their own BIOS.

November 18th, 2017, 03:39 PM
Lots of IBM AT (IBM 5170) info at minuszerodegrees.net

RAM error

I.e. The 201 error.

The "060000" (an address in hex) in the 201 error equates to the on-screen "00384 KB OK".
It is possible that your early 5170 has only 384 KB of RAM.
Whatever the amount of RAM, assuming that the RAM is good, once you configure that amount into the CMOS SETUP, the 201 error should disappear.

CMOS SETUP yet to be performed

I.e. The 161 and 163 errors.

When you press F1 key, you will note that you get taken into BASIC.
Per the information at [here (http://minuszerodegrees.net/5170/setup/5170_setup.htm)], note that you can do the CMOS SETUP via BASIC (i.e. no boot floppy required).

Also, per that web page, you will see that booting from a 720K boot diskette is possible when the CMOS SETUP has yet to be done.

November 18th, 2017, 05:18 PM
You mentioned converting the ATAD 2.07 disk to a 1.2 MB diskette.

Try creating the ATAD 2.07 disk as its original size of 360KB (on a 360KB diskette) and see if you can boot with that.

November 19th, 2017, 04:38 AM
Thanks for all the help guys - I'm going to try configuring the BIOS through BASIC and booting a DOS 6.2 disk.