The CRC is initialised to FFFF. It is updated byte by byte and uses the CCITT-CRC16 algorithm. It is written after the ID and data fields of each sector in big-endian format (high byte first and then low byte).
The main competitor of the µPD765 FDC controller on the market at that time was the WD179x FDC chip family.
The primary difference between 765 and 179x controllers is that the 765 only does standard track formats (preamble, marks and data fields), while the 179x will write anything you tell it in the write track (formatting a track) mode.
<br>