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PC Hardware in a Nutshell, 3rd Edition by Barbara Fritchman Thompson, Robert Bruce Thompson

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Understanding partitioning

Each physical disk must have at least one partition, and may have as many as four. Creating the first partition on a physical disk drive creates the Master Boot Record (MBR) for that disk and writes the MBR to the first physical sector. Subsequent changes to the partitioning of that disk, no matter which operating system makes them, update that single MBR. The MBR on each physical disk contains a section called the partition table. The partition table tells the computer and the operating system how the hard disk is logically divided and how to access the information stored on that hard disk.

There are two types of partitions. A primary partition is one from which the computer may be booted. Each primary partition is logically formatted as a single volume for a particular operating system and is assigned one drive letter. A primary partition may occupy all or part of a physical hard drive, and a single hard drive may contain from zero to four primary partitions.

The second type of partition is called an extended partition. An extended partition is essentially a virtual physical disk, which may itself be subdivided into logical volumes. A disk may contain zero or one extended partition. The computer cannot be initialized from an extended partition, although the operating system files may reside on a volume located on an extended partition.

Extended partitions are neither formatted nor assigned drive letters. Instead, extended partitions are further divided, ...

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