Double Sectors:

Although Atari specified 18 sectors per track as the standard, there is actually room for 19. One trick which has become popular has been to place 2 sectors, bearing the same sector number, within each track. The software then calls out for that sector several times. What it then does is compare the consecutive sectors of data looking for two different sectors. This will happen within 4 or 5 retries due to the laws of probability. If after four or five retries only one sector of data has been found it is assumed the disk was copied, and the program will not run. If both sectors are found of course the program runs. The code cracker has more trouble with this type of protection due to non- specific nature of the code required to check for double sectors (as opposed to a simple status check), however. Some pirates have been known to foil this type of protection. Usually the more familiar with assembly language the programmer is the easier it will be to comprehend these protection schemes.