B.3. Creating DOS partitions
There are two basic DOS partition types:
A primary partition, which is described by a partition record
in the MBR partition table.
A logical partition, which is described by a partition record
in the EBR partition table.
Every partition table has room for four partition records; however,
there are a few rules that impose limits on this.
An MBR partition table can hold four primary partition records unless you
also have logical partitions.
In this case, one partition record is used to describe an extended
partition and the start of the EBR chain that in turn describes
logical partitions.
Because all logical partitions must reside in the extended partition, you
cannot allocate room for a primary partition within the extended partition
and you
cannot allocate room for a logical partition outside or adjacent to this area.
Lastly, an EBR partition table performs two functions:
It describes a logical partition and therefore uses a partition
record for this purpose.
It uses a partition record to locate the next EBR partition table.
EBR partition tables use at most two entries.
When creating a DOS partition, the options you are presented with depend
on the kind of disk you are working with. However, both OS/2 disks and
Linux disks require that you choose a freespace segment on the disk
within which to create the new data segment. The create options are:
- size
The size of the partition you are creating.
Any adjustments that are needed for alignment are performed by the
DOS plug-in and the resulting size might differ slightly from the
value you enter.
- offset
Lets you skip sectors and
start the new partition within the freespace area by specifying a
sector offset.
- type
Lets you enter a partition type or choose from a list of
partition types; for example, native Linux.
- primary
Lets you choose between creating a primary or logical partition.
Due to the rules outlined above, you might or might not have a choice.
The DOS plug-in can determine if a primary or logical partition can be
created in the freespace area you chose and disable this choice.
- bootable
Lets you enable the sys_ind flag field in a primary partition
and disable it when creating a logical partition.
The sys_ind flag field identifies the active primary partition for booting.
Additional OS/2 options are the following:
- partition name
An OS/2 partition can have a name, like Fred or Part1.
- volume name
OS/2 partitions belong to volumes, either
compatibility or logical, and volumes have names. However, because
the DOS plug-in is not a logical volume manager, it cannot actually
create OS/2 logical volumes.
- drive letter
You can specify the drive letter for an OS/2 partition, but it
is not a required field. Valid drive letters are: C,D...Z.
