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/* FDC Track Format */
The main competitor of the µPD765 FDC chip on the market 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.
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=== GAPS Protection ===
GAPS was the most commonly used copy protection technique to protect floppy disks on Amstrad CPC. It consists of writing specific values (other than the standard &4E) in the separation area between 2 consecutive sectors.
When the protected program is launched, it checks if these special values (often a string signature) are present. If they aren't, the program can then crash or reset the computer or format the disk.
The trick is that the 765 FDC can read the custom byte values in the gaps, but it cannot write them. This made it hard for people to make working copies of protected disks.
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