Help me understand ST506 / MFM Drive interface to controller

[jeggers]

I'm new to this, and I'm trying to understand MFM drives a little better, so here's a couple of questions (I'm working on a very-low-cost MFM-Drive emulator).

I'm looking at the OEM manual for the ST506 and ST412, and it states 32 sectors/track. Google states 17 and various other numbers... But I thought an MFM drive was "dumb", why would the manual state ANY number for what's essentially BIOS / Operating-System dependent? If a controller wanted to, couldn't it format to just 1 or 3 or any number of sectors per track? I would have thought that the drive (or manufacturer) doesn't care.

When a controller wants to read/write a particular sector (after navigating to the track and selecting the head), does it use the Sync-signal from the drive to calculate the time offset to find the beginning of the sector?

When a controller wants to write actual data to the sector, does it write the entire sector, or could/does it do partial writes ?

Any help would be appreciated.

[fzabkar]

It doesn't make sense to write a partial sector. How would you compute the ECC bytes?

As for choosing the sectors per track, this AT&T 3B2 Computer uses 18:

http://www.unixwiz.net/3b2/3b2faq.html

Code:

Drive type   drv id   cyls trk/cyl sec/trk byte/cyl     abbrev
--------------- ------   ---- ------- ------- --------     ------
Wren II 30MB      3     697    5   18   512       HD30
Wren II 72MB      5    925    9   18   512       HD72
Fujitsu M2243AS      8     754    11      18      512       HD72C
Micropolis 1325    5    1024     8      18      512       HD72
Maxtor 1140      4*    918=   15   18   512       HD120
Maxtor 1190     11   1224+   15   18   512       HD135

The Micropolis manual suggests 32 sectors at 256 bytes per sector, or 33 sectors at 256 bytes per sector.

https://bitsavers.org/pdf/micropolis/101400b3_1320_1987.pdf

AIUI, the sync bytes are required to synchronise the bitclock prior to reading the sector ID, and to train the AGC circuit.

[Hardcore Games]

MFM disks are really old. Both the ST506 and ST412 are things I used back when DOS was a thing. IDE disks quickly obsoleted the old MFM/RLL period.

[WebClaw]

MFM disks are really old. Both the ST506 and ST412 are things I used back when DOS was a thing. IDE disks quickly obsoleted the old MFM/RLL period.

Has to be a bot; comments are completely useless and serve no purpose other to increase post count.