3.5" floppy drive in IBM XT?

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Tue Apr 8 17:19:01 2003

> At 10:47 PM 4/7/03 -0700, Don wrote:
> >
> >Interesting question is whether it is being used as a 21mb MFM
> >drive or as a 33mb RLL. My guess would be 21mb.
>
>
> It's an RLL drive and is 32 Mb according to my sources.

All that means is the drive is capable of handling RLL encoding
(basically, it can correctly reproduce pulses at half-multiples of the
MFM spacing (although they won't ever be closer together than
the MFM encoder would produce). Such a drive will, of course, work
correctly with an MFM controller, but will have a lower capacity when so
used (in this case 21 Mbytes).

Remember that with the ST506/ST412 interface, it's the _controller_, not
the drive that handles the data encoding/decoding. The 'data cable'
carries the raw data stream to/from the disk.

-tony
Received on Tue Apr 08 2003 - 17:19:01 BST