introduction
(from http://www.redhat.com/docs/manuals/linux/RHL-9-Manual/install-guide/ch-partitions.html)
Disk partitions are a standard part of the personal computer landscape and have been for quite some time. ...s disk drive capacities soared, some people began to wonder if having all of that formatted space in one big chunk was such a great idea. This line of thinking was driven by several issues, some philosophical, some technical. On the philosophical side, above a certain size, it seemed that the additional space provided by a larger drive created more clutter. On the technical side, some file systems were never designed to support anything above a certain capacity. Or the file systems could support larger drives with a greater capacity, but the overhead imposed by the file system to track files became excessive.
The solution to this problem was to divide disks into partitions. Each partition can be accessed as if it was a separate disk. This is done through the addition of a partition table.
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the partition table is divided into four sections. Each section can hold the information necessary to define a single partition, meaning that the partition table can define no more than four partitions.
Each partition table entry contains several important characteristics of the partition:
- The points on the disk where the partition starts and ends
- Whether the partition is "active"
- The partition's type
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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.
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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 paritions on a single disk drive.
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