Book type refers to the field of data consisting of four bits on the lead-in of a DVD, which is decoded by a DVD-ROM drive or DVD player. The book type then tells the DVD device what format (DVD-R, DVD+R, or DVD-ROM) is contained on the disc. The data included in the Book type can be changed on DVD+R discs, but currently no proven method exists to change the book type of a DVD-R disc. The ability to change book type is important as older devices can be fooled into playing DVD+R discs that have had their book type changed to that of DVD-ROM.
The book type field values are as follows: