Osborne-1 SD format

From: Eric Smith <eric_at_brouhaha.com>
Date: Mon Feb 21 19:31:32 2005

Steve Thatcher wrote:
> all Intel did was to use the same basic 3270 format and double the number
> of sectors to make the OS changes easy. The gaps between real data did not
> get as big from SD to Intel's DD.

Intel made more changes than that. In addition to the use of M2FM and
and different gap sizes, the index mark, ID address mark, data mark, and
deleted data mark don't match standard FM or MFM. The gap and PLO sync
bytes are different as well.

It's documented in the disk controller manuals. For instance, see
pages 4-25 through 4-31 of the iSBC 202 manual:

Or pages 1-4 through 1-11 of the Intellec Double Density Diskette Operating
System Harndware Reference Manual:

DEC, on the other hand, really did just subsitute a slightly modified
MFM data field for the FM data field on their RX02 disk system. The
details are in the RX02 Floppy Disk System Tecnical Manual, pages 1-10
through 1-14:

Received on Mon Feb 21 2005 - 19:31:32 GMT

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