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Atari didn't need it either. The 1771 (or 2793 I think) floppy controller chip (a standard chip for IBM formatted floppies) does need the index pulse for the write track command for formatting. But the signal is just connected to a GPIO (I think on the 1050 drive this was fed by a timer).

This saves money, eliminating the need for the index pulse LED and photo transistor.

Reads never need the index pulse on soft sector floppies. Each sector has a header with the sector number and an "address mark" (a unique data pattern) used to detect the beginning of each sector and track.

Hmm, except the index pulse may have been used for a timeout if I remember correctly.




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