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.

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


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.

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A backup a day keeps DR away.

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.

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Orico DS500C3-US-BK 5-disk 3.5" SATA, iTGZ 4x M.2 2280 Thunderbolt enclosure NVMe/SATA, etc. etc.

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