Appendix E. An Introduction to Disk Partitions

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Table E 1. Partition Types

By this point, you might be wondering how all this additional complexity is normally used. See Figure

E 6, for an example.

Figure E 6. Disk Drive With Single Partition

In many cases, there is only a single partition spanning the entire disk, essentially duplicating the

method used before partitions. The partition table has only one entry used, and it points to the start of

the partition.

We have labeled this partition as being of the "DOS" type. Although it is only one of several pos 

sible partition types listed in Table E 1, it is adequate for the purposes of this discussion. This is a

typical partition layout for most newly purchased computers with a consumer version of Microsoft

Windows  preinstalled.

E.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 E 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 E 7, shows a disk drive with one primary

partition and one extended partition containing two logical partitions (along with some unpartitioned

free space).

Figure E 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.