|Author:||Zaphod (guest: search)|
|Date:||Thu, Feb 11th, 2016 @ 19:41 ( . )|
Encounter uses TWIN SECTORS.
In this case, track 21 had 2 different sector 18s on it.
To check the protection it would seek one sector, then seek 18 and store it one place, then seek a different sector then seek 18 again and store it somewhere else.
A fast copier will only pick up one of the sector 18s, and both have to be present to pass the protection.
A nibbler will not get the gaps the same length, and throw off the timing causing the wrong sector to be loaded and also failing the protection.
This protection is interesting in that it needs no drive code.
It can be copied easily by writing the track in one pass, which will get the gaps right and put the sectors the proper relative distance apart.
It's also tricky to parameter, because you need to relocate the twin sector elsewhere, then change the code to look elsewhere, AND you need to make sure the correct sector was copied before the parameter.