MFM hard drive formats only 10/20 MB...why?

[billdeg]

USing an IBM XT 640K with an IBM 1816101 hard drive controller and a Rodime RO204 hard drive.

I "low level" formatted the drive using the IBM XT reference disk and fdisk'd with DOS 3.3. I then ran the format command /s. There were no errors, the correct number of cylinders were counted off (320cyl, 8heads) appeared.

For some reason it formatted to ~10MB not ~20MB. Do you know why that happens?

More on the Rodime RO204:
http://www.4drives.com/DRIVESPECS/RODIME/3704.txt

[mbbrutman]

I'm confused. All that I can think of is that you fdisk'ed wrong.

[Druid6900]

Bill,

Dongfeng went through this in http://www.vintage-computer.com/vcforum/showthread.php?t=3995 and it turns out it's a type 1 (10 meg) controller only.

Richard

[mbbrutman]

That is a possibility too, but he says that the format routine counted 320 cyls, 8 heads. Which it shouldn't .. that controller should only do 302 cyls, 4 heads.

[rmay635703]

That controller doesn't match that drive, you are lucky it works at all.

I have gone through this with XT controllers more times than I can count, a few later western digital controllers would support multiple MFM formats but even they were a bit of a pain and many times did not support every drive.

Also even though the SOFTWARE reports the correct number of cylinders does not mean the controller will use them, that controller only will work one way and is setup hard for that configuration regardless of whether or not the software can see what should be there.

Cheers
Ryan

[billdeg]

thanks for the explanation. Also, perhaps I am wrong about how many heads/cylinders were reported.

I have an XT system that I use for testing disk drives, and I guess I better get a new controller, one that is more flexible. I did not know that the old stock IBM controller was limited. That explains a few mysteries!

[dano]

Unfortunatly the boards are hard-coded for one drive type, or have a few selectable through dip switches or jumpers. The best I've found are Seagate controller that auto-detect the drive.... though they may be limited to Seagate brand drives. Recently I've started using Furute Domain SCSI controllers, it makes life much easier! Maybe we should setup a database of controllers, jumper settings, and drives supported? I have some old Everex documentation that is worth it's weight in gold....