Installation guide

Appendix D. An Introduction to Disk Partitions 75
D.1.3. Partitions within Partitions — An Overview of Extended
Partitions
Of course, over time it became obvious that four partitions would not be enough. As disk drives
continued to grow, it became more and more likely that a person could configure four reasonably-
sized partitions and still have disk space left over. There needed to be some way of creating more
partitions.
Enter the extended partition. As you may have noticed in Table D-1, there is an "Extended" partition
type. It is this partition type that is at the heart of extended partitions.
When a partition is created and its type is set to "Extended," an extended partition table is created. In
essence, the extended partition is like a disk drive in its own right — it has a partition table that points
to one or more partitions (now called logical partitions, as opposed to the four primary partitions)
contained entirely within the extended partition itself. Figure D-7, shows a disk drive with one primary
partition and one extended partition containing two logical partitions (along with some unpartitioned
free space).
Extended
OS/2 HPFS
Linux native
DOS
Figure D-7. Disk Drive With Extended Partition
As this figure implies, there is a difference between primary and logical partitions — there can only
be four primary partitions, but there is no fixed limit to the number of logical partitions that can exist.
However, due to the way in which partitions are accessed in Linux, you should avoid defining more
than 12 logical partitions on a single disk drive.
Now that we have discussed partitions in general, let us review how to use this knowledge to install
Red Hat Enterprise Linux.
D.1.4. Making Room For Red Hat Enterprise Linux
The following list presents some possible scenarios you may face when attempting to repartition your
hard disk:
• Unpartitioned free space is available
• An unused partition is available
• Free space in an actively used partition is available
Let us look at each scenario in order.
Note
Keep in mind that the following illustrations are simplified in the interest of clarity and do not reflect
the exact partition layout that you encounter when actually installing Red Hat Enterprise Linux.