Technical information

© Jean Louis-Guérin – V1.2a – September 2014 Page 45 / 69
For the standard partition description, the definitions of the fields in the partition table entry are:
Offset
Length
Description
$00
1
Flag: indicate the state of the partition
 bit 0 when set partition exist,
 bit 1-7 reserved
$01
3
Id: a 3-bytes ASCII field that identifies the type of partition
 GEM for regular (< 32MB) partition
 BGM for big (≥ 32MB) partition
$04
4
Offset to the beginning of the standard partition from the beginning of the extended
root sector that this structure reside in. In number of physical (512 bytes) sectors
$08
4
Size of the partition in number of physical (512 bytes) sectors
For the link to the next partition, the definitions of the fields in the partition table entry are:
Offset
Length
Description
$00
1
Flag: indicate the state of the partition
 bit 0 when set partition exist,
 bit 1-7 reserved
$01
3
Id: a 3-bytes ASCII field that identifies the type of partition
 XGM must be used
$04
4
Offset to the beginning of the next subdivision from the beginning of the entire
extended partition. In number of physical (512 bytes) sectors
$08
4
Size of the partition in number of physical (512 bytes) sectors
9.4.2 Example of layout with TOS extended partitions
In the following example we have a hard disk with 3 standard partitions and an extended partition that
contains two standard partitions. The Root Sector contains 3 pointers to the 3 standard partitions and
a pointer to the extended partition that starts with the first Extended Root Sector. This ERS contains
a pointer to a standard partition and a pointer to the next Extended Root Sector. The second ERS
contains only a pointer to the second standard partition as it is the last in the chain.