ATIP = Actual Time In Pre-Groove...
atip information is only present on rw material, you'll never find it on pressed disks (silvers) for example, and its often used as a 'backup' check for some protections (note: that a cd reader unit - ie : NOT a burner, will also return nothing on an atip check)..
the atip contains information like the dye used on the disk, max writing speed etc, and information that sometimes allows you to track it back to the manufacturer (to detect forged/fake disks and so on)... apart from that its not that interesting..
http://en.wikipedia.org/wiki/ATIP
some of the info there is wrong, like the "ATIP information is only readable on CD-R and CD-RW drives, as normal drives don't need the information stored on it." line... but apart from that (and the fact that it doesnt mention dvd-r/rw etc) the information should be enough to satisfy your curiousity
