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Hard disk drive partitioning

In the field of computer engineering, hard disk drive partitioning is the creation of logical divisions upon a hard disk drive that allows one to apply operating system-specific logical formatting.

Disk partitioning is a simple technique which can be viewed as a precursor of Logical volume management[?].

Drive partitioning on non- IBM PC architectures

~to be written~

Drive partitioning on the IBM PC

For an detailed discussion of how partitioning is implemented in the IBM PC architecture, see Partition (IBM PC). The rest of this article will concentrate on the practical aspects of PC hard drive partitioning.

Partitioning is done for several reasons:

  • Some filesystems (e.g. old versions of the Microsoft FAT filesystem) have size limits smaller than a modern disk drive.
  • If one partition becomes corrupt, you can attempt to salvage data onto another partition.
  • Swap partitions have to be separate from filesystem partitions.
  • To prevent overgrown log or other files from making the whole computer unusable, they are put on their own partition.

Numerous partitioning schemes have appeared during the years, for almost all computer architectures in existence. Many of them are relatively transparent and allow convenient manipulation of the disk partitions; some however are obsolete in design and are accompanied by numerous quirks.

The partition table, as used in the IBM PC architecture, was first devised in late 1980s, when hard drives were coming into use. It is a simple table, consisting of up to 4 records, each of which indicating where does the partition start, where does it end and what is its type. In addition, an "active" flag is provided, that tells the Master Boot Record from which partition to boot.

This scheme is widely considered obsolescent, because it allows for only 4 partitions (later, an expansion of this format that provides for "container" logical partitions that contain up to 4 secondary partitions inside themselves eased this problem somewhat, though by no means solved it), and because it has certain compatibility problems with hard drives bigger than 8 gigabytes in size. As the IBM PC architecture is extremely common, the partition tables are likely to stay for a while. However, a recent project of Intel and Microsoft called the Extensible Firmware Initiative (EFI[?]) has a component called GUID Partition Table (GPT) that will, perhaps, provide a much better solution from the problem on future generations of PCs.

Legacy partition tables are complicated to administer, and have numerous quirks. The reader that is interested in modifying his partition table is strongly advised first to study these quirks, and only then modify the drive. In addition, it is strongly recommended to do the modifications only using properly tested software, such as PowerQuest's Partition Magic.

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