The scheme defines the overall organization of the drive, which can feel pretty obscure, because you rarely need to change it. You can select among GUID Partition Map, Master Boot Partition, and ...

However, there's an asymmetry here. Although a PPC machine cannot boot up from a GUID-partitioned disk, an Intel machine can boot up from an Apple partition scheme disk.

Depending on the partition scheme, these are the file systems Mac OS 10.4 supports: Mac OS Extended or HFS+ is an improved version of Apple's Hierarchical File System from the mid-1980s.