Extended Partition Tables

This is a discussion of extended partition tables related to my web pages discussing the boot process with emphasis on the MBR and boot code for Windows 95 OSR2.

The extended partition tables below are from a PC originally formatted under WFWG 3.11 and then upgraded to Windows 95a in a separate primary partition. Thus one primary partition contains WFWG 3.11 and the other contains Windows 95a even though the MBR table below shows one of the primary partitions as being Non-DOS.


Example of Extended Partition Tables

Example of a hard drive partitioned with DOS FDISK that has two primary partitions, each with its own OS, and one extended partition with several logical volumes (partitions). Actually the second Primary partition was obtained using PartitionMagic as DOS FDISK only allows one primary and one extended. The partition tables below are displayed in the same format as used by Norton's Disk Editor in Partition Table view. Note that (MBR only) the column labeled "Relative Sectors" is equivalent to the "Starting Sector" of the partition in LBA format.

Partition Table in MBR
Physical Sector: Cyl 0, Head 0, Sector 1

System

Boot
Starting Location Ending Location Relative
Sectors
Number of
Sectors
CylinderHeadSectorCylinder HeadSector
BIGDOSYes011 12925463632,088,387
Non-DOSNo13001 254254632,088,4502,008,125
EXTNo25501 1022254634,096,57512,337,920
UnusedNo000 00000

Notes on MBR

First partition table in Extended Partition
Physical Sector: Cyl 255, Head 0, Sector 1

System

Boot
Starting Location Ending Location Relative
Sectors
Number of
Sectors
CylinderHeadSectorCylinder HeadSector
BIGDOSNo2551 138225463632,056,257
EXTNo38301 510254632,056,3202,056,320

Notes on EBR

Second partition table in Extended Partition
Physical Sector: Cyl 383, Head 0, Sector 1

System

Boot
Starting Location Ending Location Relative
Sectors
Number of
Sectors
CylinderHeadSectorCylinder HeadSector
BIGDOSNo3831 151025463632,056,257
EXTNo51101 638254634,112,6402,056,320


Last partition table in Extended Partition
Physical Sector: Cyl 895, Head 0, Sector 1

System

Boot
Starting Location Ending Location Relative
Sectors
Number of
Sectors
CylinderHeadSectorCylinder HeadSector
BIGDOSNo8951 1102225463632,056,257

Boot sectors in logical drives contain code that is similar to the boot code in the main boot sector, but since extended partition volumes cannot be booted, this code generally displays a message stating that an extended volume cannot be booted.This code is not discussed further. Each boot sector also contains its own BPB for the current logical volume.

Additional sources of information:


MBR/Boot Index

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This page was created on 18 December 2000, last updated on 13 January 2001.