Following are excerpts from the Unofficial DVD specifications Guide 2.2 ebook.

...The following illustration shows common configurations of PGC:



1. PGC1 contains pre-commands. These commands are executed before the cells are played back. PGC1 has 7 cells which correspond to the actual cells A-G physically located on the disc. The sequence order of the cells to be played back is the same as that of the cells on the disc. PGC1 has three chapters, PTT1-PTT3. The first chapter (PTT1) has one program (program 1). The second chapter (PTT2) has two programs (program 2 & 3), and the last chapter has one program (program 4). Program 1, 2, 3, and 4 has 2, 1, 1, and 3 cells accordingly...

The left and top illustration show a typical hand-held remote control unit and a DVD players that use the symbol to indicate the "previous" program selection, and the symbol to indicate the "next" program selection. Since most commercial movie DVDs assign one program per chapter, these buttons initiate the previous or next chapter selection.

2. PGC2 does not have pre-commands so cell 1 is played back if PGC2 is linked to. PGC2 has 5 cells which correspond to the actual cells A, B, E, F, and G physically located on the disc. The sequence order of the cells to be played back is not the same as that of the cells on the disc. PGC2 has two chapters only. Since PGC2 has post-commands, these commands are executed immediately after the playback of cell 5.

3. PGC3 does not have any cells to playback. The pre-commands are executed and then the post-commands are executed. PGCs which do not contain cells are used to direct and control the playback sequence of movie titles on the DVD.

For a complete coverage of a PGC, visit the section on functions and structure of a PGC.