floppy low level format question

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Jun 11 18:05:32 2004

> The information I have gives the makeup of each of the gap types in
> terms of bit patterns, counts, what clock transitions are missing for
> MFM formats etc.
>
> Question is, is this a standard? I mean, for any disk using MFM or FM
> recording are these bit patterns going to be the same? Or is it
> dependant on the controller chip being used?

It's sort-of a standard for standard controllers (the sort-of because the
WD1771, for example, could read/write a couple of data markers that no
later controller could write -- and the TRS-80 Model 1 used one of
them...). That's why you can read a disk formated on an HP9114 (WD2797
controller IIRC) on a PC (Intel 8272 controller).

However. it's not standard on non-stnadard controllers, meaning DEC M2FM
(RX02), any of the GCR ones (Apple ][, older Macs, Commodore Pet/C64
drives ,etc).

-tony
Received on Fri Jun 11 2004 - 18:05:32 BST