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The standard boot sector is limited in the fact that it only has direct support for 4 partitions.  Extra partitions are added by chaining new partition tables.  It works, but is rather messy. 

A new standard is the Extensible Firmware Interface (EFI) an Intel replacement for the Master Boot Record (MBR) that is stilled on PCs.  Current Apple OS/X systems use this new partition layout. It is an option on Vista, and essential to create partitions that exceed to TB. The existing boot sector only has space for 32 bit sector numbers, the new system handles 64 bit sector numbers - should be a few years before that becomes a limitation.

The structure is that the MBR looks like a normal boot sector, with a single partition entry.  The critical point is the the file system is defined as 0xEE, rather than say NTFS, or FAT16.  The first sector is marked by the string "EFI PART".  The following sectors contain the specific partitions with a 128 byte record for each partition.

Each partition entry is identified by 2 16 byte GUID (Globably unique indentifier).  It then contains both start and end sector number, and a text description of the partition such as "Apple_HFS_Untitled_1"

CnW Recovery software reads this type of header and determines the disk type.  The program currently supports Apple HFS+ partitions and Windows Data partitions, as may be found on Vista drives.  See the section on recognising sector types for more details