Part of the Computing fundamentals glossary:

WARNING: Use caution when repartitioning a hard disk drive that contains data. Repartitioning wipes out all data on the disk. Be sure to back up everything to another storage medium first.

FDISK is a utility, included in all versions of MS-DOS and Windows, for formatting (preparing) a hard disk drive to hold data and to logically partition the disk, specifying and naming major portions of it for different uses. FDISK is used to prepare and partition a brand new hard drive, and typically most personal computers today arrive with the drive already partitioned and loaded with the operating system and perhaps other software. A typical personal computer today arrives with a single partition that is addressed by the operating system as the logical C drive. (Some PCs also have one or two diskette drives addressed as the A and B drives. PCs with CD-ROMs also usually address the CD-ROM as the D drive. But a hard disk drive can be divided into and addressed as several "logical" drives, or partitions.)

In addition to setting up a new hard disk drive, FDISK is used for repartitioning the hard drive when you want to change something. For example, a computer can be set up as a dual boot system, with one operating system (for example, Windows 2000) in one partition and another operating system (for example, Linux) in another partition. Disk partitioning is also commonly used on LAN servers, where different sets of users share different files and applications. The maximum partition size in the first version of DOS to use FDISK was 16 megabytes. Recent Windows systems support hard drives up to 2 terabytes (2,000 gigabytes) in size!

If you need to repartition your current hard drive, be sure to back up all data because it will be lost when you use FDISK. Be careful to follow the documented Microsoft and manufacturer directions.

The age of your computer and the operating system you use determines how difficult the hard drive installation will be. The Basic Input Output System (BIOS) in computers manufactured before 1994 does not support drives larger than 512 MB, which causes FDISK to display larger hard drives as only 512 MB in size. It is necessary to use disk management software that helps an older BIOS version to recognize a hard drive larger than 512 MB. Disk management software is usually included with your new hard drive or free upon request from the hard drive manufacturer. You can also purchase a BIOS upgrade such as an EPROM chip, flash memory BIOS software, a controller card, or a card with a BIOS chip on it depending on the manufacturer's recommendation. Depending on your operating system, you may have to create multiple partitions in order to use your hard drive's full capacity:

  • DOS version 6.22 and later supports drives greater than 8.4 GB. Versions earlier than 6.22 do not.
  • Windows 95A does support drives larger than 8.4 GB, but you have to partition the drive into at least four partitions depending on the hard drive's size because of FAT 16 file system's limitations used by Windows 95A. Windows 95B supports FAT 32, which allows one large partition on new hard drives and supports hard drives up to 2,000 GB in size.
  • The first and later editions of Windows 98 support FAT 32 and hard drives up to 2,000 GB.
  • Windows NT version 5.0 and later also supports large hard drives.

FDISK has its limitations. You can't move applications from one partition to another without uninstalling and reinstalling the software. FDISK erases all data on your hard drive. And you can't delete or create new partitions without going through the entire FDISK and formatting process again. However, special partitioning software such as PartitionMagic can be used instead of FDISK. Partitioning software allows you to create, delete, and resize partitions without losing your data. You can move applications from one partition to another without uninstalling and reinstalling the application. You can hide partitions to protect data from other users. You can also use partitioning software as a boot manager. A boot manager allows you to install and use more than one operating system easily. Partition software also eliminates the need for a BIOS upgrade in older computers.

This was last updated in September 2005
Contributor(s): Errie and C.J. Garibay
Posted by: Margaret Rouse

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