View Full Version : MFM disk on AT?

April 25th, 2006, 07:37 AM
Can I use Western Digital MFM HDD from XT computer on AT machine? Of course I have controller.

April 25th, 2006, 07:52 AM
I don't think that I would try it .. In theory it is just another 8 bit peripheral, but there are some signifcant differences between XTs and ATs with regards to hard disks:

- ATs expect the controller to be on IRQ 14. XTs have it on 7 usually.

- ATs have hard disk support built into the BIOS. XTs provide it on the card.

- ATs expect a 16 bit interface to the drive controller. XTs only have an 8 bit interface.

If you could disable the AT onboard controller it might work. On an genuine IBM AT that is not possible.

April 25th, 2006, 08:28 AM
That computer have 16bit HDD/FDD IDE controller not build in to mainboard but it's in 16bit slot. There were 10-20 MB IDE drives? If not, what is usage of some disk drives types in BIOS?

Terry Yager
April 25th, 2006, 09:03 AM
Depends on the BIOS. Some early IBM versions had as few as 15 recognized drive types. Later versions (and most clones) included many more types, and (usually) a user-definable type, where the user enters the parameters (c/h/s) manually. Type #44 was commonly user-definable.


May 6th, 2006, 09:50 AM
Finnaly I have connected hard card to 8bit slot and it work fine, but hard disk is bad sectored so I made low level format, but now DOS don't recognize this drive. Why?

May 6th, 2006, 12:56 PM
Did you use FDISK to set up the partition?

May 6th, 2006, 09:56 PM
I forgot about FDisk :D . It works fine on AT without any problems.

May 7th, 2006, 02:09 AM
Hello Luke

What software did you use to low level format the disk?
I may need to do the same thing as you are doing.

May 7th, 2006, 12:12 PM
It's easy, just get MFM drive working and try G=C800:0005 in debug, this will start program from MFM controller that will format your drive.

May 7th, 2006, 02:26 PM
Not necessarily true .. that assumes that the controller has a BIOS extension starting at C800, and that a low level format routine can be found at that address.

If you jumpered the hard disk to another BIOS area, adjust accordingly. Also, many XT class controllers *do not* have the format routine on disk. They do have a built-in BIOS service that can do it, but you have to call it from a program .. it's not 'interactive' like the example referenced above. The original XT controller falls into this category .. you need the Advanced Diagnostics disk to do a low-level format.

May 11th, 2006, 10:09 AM
WDFMT is for IDE-AT drives... I haven't found any utillity to low level format MFM drive. Wrong thread :S...

May 29th, 2006, 03:01 AM
Re "If you could disable the AT onboard controller it might work. On an genuine IBM AT that is not possible."

I used to work on genuine IBM AT's. To disable the onboard hard disk controller, just set the drive type to zero.

May 29th, 2006, 06:43 AM

Original IBM ATs don't have onboard controllers. The controller is in a slot. It's a full sized card based on a Western Digital chipset.

The BIOS of the machine has the hard disk BIOS built in, unlike on an XT. When you set the drive type to zero, you are just telling the machine not to try to bother using a hard disk with the built-in BIOS.

Presumably, another card with a BIOS extension will be found and will drive a hard drive. And it's quite possible that the other card doesn't even have a hard disk interface - it could use the original controller card in the machine! (As long at the replacement BIOS knows where to find the hardware, it really doesn't matter where it lives.)

May 29th, 2006, 04:40 PM
Yes, you are right. I was careless in my response. My "hard disk controller" should have perhaps been "hard disk code".

What I was trying to indicate was that if you have a genuine IBM AT and you want to fit a HDD controller that has a BIOS, then set the drive types in the AT's setup to zero. note that I'm not saying that any HDD controller with a BIOS will work in an AT. The controllers I'm referring to are usually specialist boards (eg. to support hard drive encryption) that are designed for the AT.

May 29th, 2006, 05:00 PM
Gotcha. Just doing my part to keep things clean and accurate.

SCSI cards and add-on IDE cards generally use this technique as well, as they both provide their own BIOS and don't want the system BIOS to try to do anything. As you noted, setting the CMOS drive types to 0 effectively neuters the on-board BIOS support for booting from a hard disk.