1.1.1 Partition Table Contents

A partition table consists of four 16 Byte entries. Each entry contains the following data:

Bootable Partition Flag

The bootable flag lets the DOS boot loader know that the partition can be booted. MS DOS requires that only one partition be marked as bootable or active. If more than one partition is marked active a message like ‘Invalid partition table’.

Starting CHS

The starting CHS2 tells where the partition starts on the hard drive physically.

System Indicator Byte

The system indicator is a single byte that describes the file system that resides on the partition. Each file system type has a file system ID. For instance, a primary FAT 16 partition that is larger than 32 Mb would have a file system ID of 06h. One major limitation of the system indicator byte is that it is only 8 bits, which provides only 256 unique file system types. Setting this byte in a partition table entry to a value that is unrecognized by DOS would make DOS ignore that file system.

Ending CHS

The ending CHS tells where the partition ends on the hard drive physically.

Relative Sector Offset

The relative sector offset is the number of sectors before the partition on the disk. It could also be described as the number of sectors between the starting CHS and cylinder 0, head 0, sector 1.

Sector Count

The total number of sectors in the partition


Footnotes

(2)

CHS stands for Cylinder/Head/Sector used in referencing physical drive geometry. For more information read Upgrading and Repairing PCs by Scott Mueller, published by QUE Corporation.