| Red Hat Linux 8.0: The Official Red Hat Linux System Administration Primer | ||
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Partitions are a way of dividing a disk drive's storage into distinctly separate regions. Using partitions gives the system administrator much more flexibility in terms of allocating storage.
Because they are separate from each other, partitions can have different amounts of space utilized, and that space will in no way impact the space utilized by other partitions. For example, the partition holding the files comprising the operating system will not be affected even if the partition holding the users' files becomes full. The operating system will still have free space for its own use.
Although it is somewhat simplistic, from this perspective you can think of partitions as being similar to individual disk drives. In fact, some operating systems actually refer to partitions as "drives". However, this viewpoint is not entirely accurate; therefore, it is important that we look at partitions more closely.
Partitions are defined by the following attributes:
Partition geometry
Partition type
Partition type field
Next, we will explore these attributes in more detail.
A partition's geometry refers to its physical placement on a disk drive. In order to understand geometry, we must first understand how data is stored on a disk drive.
As the name implies, a disk drive contain one or more disks coated with a magnetic material. It is this material that actually stores the data. The surface of each disk is read and written by a head, similar in function to the head in a cassette tape recorder.
The head for each disk surface is attached to an access arm, which allows the heads to sweep across the surfaces of the disks. As the disks rotate under the heads, the section of the disks under the heads at any given position of the access arm make up a cylinder (when only one disk surface is involved, this circular slice of magnetic media is known as a track). Each track making up each cylinder is further divided into sectors; these fixed-sized pieces of storage represent the smallest directly-addressable items on a disk drive. There are normally hundreds of sectors per track. Present-day disk drives may have tens of thousands of cylinders, representing tens of thousands of unique positions of the access arm.
Partitions are normally specified in terms of cylinders, with the partition size is defined as the amount of storage between the starting and ending cylinders.
The partition type refers to the partition's relationship with the other partitions on the disk drive. There are three different partition types:
Primary partitions
Extended partitions
Logical partitions
We will now look at each partition type.
Primary partitions are partitions that take up one of the four primary partition slots in the disk drive's partition table.
Each partition has a type field that contains a code indicating the partition's anticipated usage. In other words, if the partition is going to be used as a swap partition under Red Hat Linux, the partition's type should be set to 82 (which is the code representing a Linux swap partition).