The ATIP (Absolute Time-In Pregroove), contains information about the blank CD. This information is required, so that the drive knows what kind of disc it is writing to, and so that it does not stray from the spiral it is supposed to write in.
The Main Data Channel (The area in which data is actually written), is 650 nm wide, and is shown in red.
The ATIP wobble, is approximately 22.05 kHz, and includes information by modulating the wobble frequency. The wobble is 1000 nm wide, and is shown in black. Because the wobble is so much wider than the Main Data Channel, and because the wobble is so slight, you can burn inside of it without damaging it, or make it unreadable in any way.
Note that normal CD-ROM's and DVD-ROM's cannot read the ATIP, since it is only needed for CD-Writing. It can be used in copy protections, by checking to see if ATIP info is present. Since the ATIP does not exist in pressed CD's (The kind that come from the manufacturing plant), if it is present, in can be presumed that the CD is a copy. This kind of protection can only be defeated by reading the disc from a drive which cannot detect the ATIP info, or using utilities such as Daemon Tools and CloneCD's "Hide CDR" features, which block all requests for the ATIP info sent to the drive.