FDISK

With FDISK you can create or delete harddisk partions or logical drives.

First of all, let me explain what I mean by partitions or logical drives.
The term partition is often used when logical drive is meant, just as the term disk is often used when partition or logical drive is meant.

When I use the word disk, I mean the physical harddisk: a piece of hardware installed (I hope) in your computer. A harddisk needs to be partitioned - divided into partitions - to be of any use.

A partition is no more than an entry in the partition table, which is located at the very "beginning" of the hard disk's storage space.
Each entry in the partition table specifies the starting and end positions of the partition, the type, size and file system of the partition.
Each disk can only contain 4 partitions!

To overcome this limitation, the extended partition was introduced.
An extended partition can be subdivided into many logical drives, whereas the original primary partition can only contain 1 single logical drive.
The logical drive is what is usually referred to as drive or partition, and will usually be assigned a drive letter C: through Z:

This brings us to the next limitation in disk partitioning:
Each extended partition can only contain 24 logical drives.
Why 24?
Because logical drives can only be assigned a drive letter C: through Z:. C: is always reserved for the active primary partition, so if you have one or more primary partitions on the same disk, the number of logical drives in the extended partition is even limited to 23.

Note that this limitation no longer applies for Windows 2000 and XP, these Windows versions do not need drive letters for each partition.
Neither did this limitation ever apply to Unix/Linux, since they do not, nor ever did, use drive letters at all.

Say your disk has 3 primary partitions and 1 extended partition. Only 1 primary partition can be active and will be assigned drive letter C:. The other 2 primary partitions will not be assigned a drive letter and are "invisible" to the running operating system.
Logical drives in the extended partition will be assigned drive letters D: through Z:, 23 at maximum.
If a second harddisk is used, an active primary partition on that disk will be assigned drive letter D:, which leaves only 22 drive letters for the extended partitions on both disks.

I know it sounds pretty outdated and obscure, but if you can get a copy of OS/2 2.0 or 2.1's installation guide, it contains a detailed description of harddisk partitioning, that is valid for all Intel based computers and operating systems.

I found most of the undocumented options for MS-DOS' FDISK on Michael Jacobsen's Undocumented FDISK page, which — unfortunately — seems to be discontinued.
However, a copy is still available here.
For obvious (I hope) reasons I did not test all options, yet.
Be carefull, only experiment on systems that need to be reinstalled anyway.

More information on FDISK can be found at FDISK.com's FDISK page

Unfortunately, there seems to be no way to delete existing partitions with MS-DOS' FDISK.
Older versions of Symantec Ghost came with a utility called GDISK, a completely "scriptable" FDISK replacement. GDISK can wipe partitions. However, as far as I know, GDISK is no longer being sold.

You could, of course, use OS/2's FDISK. No need to install the entire OS, the boot diskettes that came with OS/2 are sufficient:

ChkFdisk is an example using OS/2's FDISK options to check and change the active partition at bootup.

Related Stuff:

• DISKPART: manage disks, partitions, and volumes, either by using scripts or interactively