[PostThisTooFast]

Some drives (like those for Atari 8-bits) were intelligent, so software didn't have direct control over the recording parameters. So publishers would create custom authoring drives that could write bad sectors on command; the program loader would check for a bad sector and refuse to load if it wasn't present.

A more-clever technique would write two sectors in a row with the same sector number but different data in each. The program loader would rapidly demand that sector twice, getting different data as the disk passed under the read head. A copy program, however, would only copy each sector once and be missing the data from the sector with the duplicate number.

[userbinator]

A more-clever technique would write two sectors in a row with the same sector number but different data in each.

This is also done in some optical disc copy protections, although the identically numbered sectors are far apart, causing seeks from the end to return different data than seeks from the beginning of the media.

[seryoiupfurds]

Hey @PostThisTooFast, you seem to be shadowbanned based on two flagged comments when your account was new in 2015.

Hey @dang, this account has made many good comments since then.