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This floppy disk controller chip was used in IBM AT compatible machines. It happened that I am currently developing some firmware for it to control FDDs. The circuit and driver are developed and perform properly, the only one thing bothers me:

If I recall back in 90s, IBM PC storage controller BIOS was somehow able to identify the type of drive connected - 1.2M or 1.44M.

The difference must be in supported data rate (when setting up for data transfers), and number of sectors per track (when formatting and accessing media).

Looking to the datasheet of the 37C65 (I use chip SMC37C65C), I can not understand how this identification can be done. There's no status bit showing the number of heads or possible sectors per track; the supported data rate; and performing read command with no diskette will most probably terminate abnormally with invalid C/H/S values (however I did not try).

Anyone has knowledge on the subject?

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  • \$\begingroup\$ It was a BiOS setup \$\endgroup\$
    – D.A.S.
    Commented Mar 31, 2018 at 0:50
  • \$\begingroup\$ I recall the difference simply a control register bit to read at 300 RPM or 360 RPM or 1.2 x capacity using MFM \$\endgroup\$
    – D.A.S.
    Commented Mar 31, 2018 at 1:09
  • \$\begingroup\$ @TonyStewart.EEsince'75 correct, and different track layout when formatting. \$\endgroup\$
    – Anonymous
    Commented Mar 31, 2018 at 7:04
  • \$\begingroup\$ So what information are you having difficulting locating. The FDD manuals are online. I spent 11 years in HDD magnetic recording in MFG and Test Engineering but know a little bit about FDD's \$\endgroup\$
    – D.A.S.
    Commented Mar 31, 2018 at 8:52

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