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Fdisk Command

FDISK is the utility provided with all versions of MS-DOS and Windows95/98 for partitioning hard drives. Partitioning a hard disk defines areas of the disk to be used by operating systems as volumes. In DOS, each volume is assigned a drive letter. A disk must be partitioned with FDISK before it can be formatted, even if the disk is to be left as one volume.

FDISK Version History:

MS-DOS 2.x - First DOS version to support hard drives. Maximum partition size - 16MB.

MS-DOS 3.2 - Maximum partition size - 32MB No extended partitions supported.

MS-DOS 3.3 - Maximum partition size - 32MB First DOS version to allow extended DOS partitions. Maximum number of partitions - 24 (C: through Z:)

MS-DOS 4.x - Maximum partition size - 2.1GB Maximum number of partitions - 24

MS-DOS 5.x - Same as DOS 4, but now handles up to 8 physical drives

MS-DOS 6.x - Same as DOS 5

Windows95 - (MS-DOS 7) Basically the same as DOS 4/5/6 but adds 2 new partition types - 0E and 0F - which will be seen as NON-DOS partitions by earlier DOS versions. Type 0E is used for a Primary partition if INT13 Extension support is present in the BIOS. Type 0F is used for an Extended partition if INT13 Extension support is present.

WIN95B(OSR2) Adds support for FAT32. Adds 2 more new partition types 0B and 0C. 0B is used for a FAT32 partition. 0C is used for a FAT32 partition if INT13 Extension support is present. Type B and C partitions are seen as NON-DOS partitions by earlier DOS versions (including WIN95/WIN95A).

Some Rules of FDISK:
Under DOS, the first physical drive must be the boot drive. The first physical drive must contain a primary DOS partition and the primary partition must be the first partition on the drive. A drive can have only one primary DOS partition. The partition must be active in order to boot. Only partitions on drive 1 can be made active. Only drive 1 has to have a primary partition. Additional drives may be defined either as primary or as extended partitions. In addition to or instead of a primary partition, a drive may also have one extended partition. All volumes in extended partitions must further be defined in FDISK as logical DOS volumes. DOS through FDISK assigns drive letters first to all primary partitions in order, starting with the letter C, and then to all logical volumes in extended partitions. Drive letters A and B are reserved for floppy drives. Existing partitions must be deleted with FDISK before new partition scan be defined. FDISK from MS-DOS 4.01 and earlier will not remove NON-DOS partitions.

Some Considerations for Large Drives DOS 6.22 FDISK Does not support drives over 8.4GB. Will show total drive size for drives over 8.4GB as 7553MB or 8025MB or some similar value which will vary depending on how the drive is being handled by the BIOS.Also cannot correctly display the size of large drives - is limited to 4 characters (9999MB).

WIN95/WIN95A FDISK
Does support drives over 8.4GB, but is still limited. For drives over 8.4GB, the BIOS must support INT13 Extensions. If FDISK is started with /X option, it will be limited to 8.4GB total size and 0E or 0F partition types will not be used. Also still has same problem with displaying size of large drives.

FDISK will see only 8.4GB of a drive larger than 8.4GB if FDISK is used in a DOS window or through the Run box on the Start menu. To correctly set up a drive larger than 8.4GB, FDISK must be run in DOS mode. This can be accomplished by booting to "Command Prompt Only" from the Startup menu, or choosing "Restart in MS-DOS Mode" from the Shutdown menu, or just booting from a WIN95 startup disk.

WIN95B (OSR2) FDISK
Adds support for FAT 32, which allows single partitions up to 2 terabytes (2000 gigabytes). Will always first ask "Do you wish to enable large disk support?" What this means is "Do you wish to use FAT32?" Answering NO to this question still allows support for large drives. The /X option limits FDISK to 8.4GB total size, even if answering YES to "Do you wish to enable large disk support?". FAT32 can be used on any drive over 512MB.

The problems with displaying the size correctly are fixed in the WIN95B version of FDISK. However, the FORMAT command, which also does not display large sizes correctly, is still not fixed.

The problem with FDISK not seeing drive capacity beyond 8.4GB in a DOS window is fixed. WIN98 FDISK Problem with size shown by FORMAT command while formatting drive is still not fixed.

Explanation of * Remote * in Volume Label field in FDISK
In some cases, if an existing logical drive is not recognized, FDISK will show * Remote * in the Volume Label field for that drive. This can occur if a logical drive is not recognized by FDISK for some reason and if another drive such as CD-ROM drive or RAMDRIVE or network drive is using the drive letter that the logical drive would have been assigned. One reason that a logical drive might not be recognized is that the partition type may not be valid for that version of FDISK. We have seen a case where a logical drive showed up normally in WIN98 GUI mode or in FDISK in a DOS box, but the drive label field showed * Remote * in FDISK in DOS mode (with a RAMDRIVE loaded). In this case, when booting to Safe mode/Command prompt only, FDISK showed the partition but without the volume label (which dids how up in a DOS box) and the drive was not accessible. In this case the user had copied WIN95 from an old drive to a new drive installed as master, then installed WIN98 on top of WIN95, then converted the partition on the main drive to FAT32. The * Remote * string in the Volume label field is not meant as a volume label but is meant to indicate that FDISK thinks this drive maybe a network drive.

FDISK SWITCHES
/MBR - Recreate Master Boot Record on disk 1
This function is handy when an virus has infected the Master Boot Record. With /MBR you can wipe-out the virus.

FDISK does not build an MBR on any drive except the primary master. FDISK will only create an MBR on the primary master drive if the drive does not already have a valid MBR. The 55AAh signature at the end of the sector is checked by FDISK, if not present the MBR is written. Also if the drive is blank, an MBR is written.

FDISK /STATUS
displays partition information without starting FDISK and navigating thorough the menus. This works with MS-DOS version 5.00and higher. The first sector on the hard drive, (cylinder 0, head 0, sector 1) contains the master partition boot record. This 512-byte sector contains the partition loader and the partition table. At bootup, the BIOS loads the partition loader, the partition loader loads the bootstrap loader for the bootable partition and the bootstrap loader loads the operating system.

/PRI
Create primary partition. Partition is set to active Create a primary partition on disk number <disk> with the size of <size>. The partition is set to active. FDISK /PRI:<size> <disk>

If <size> is larger than the space on the HD all space is used for the primary partition.

/PRIO
Create primary partition with FAT16/FAT32 override. Partition is set to active

Works as /PRI.

/EXT
Create extended partition

Create an extended partition (to hold logical drives) on disk number <disk> with the size of <size>.

FDISK /EXT:<size> <disk>

If <size> is larger than remaining free space, all free space is used. That is, you don’t have to know the exact remaining size in order to use this switch.

/LOG
Create logical drive

With /LOG you create a logical drive with the size of <size>. /LOG must be used together with /EXT.

FDISK /EXT:<size> <disk> /LOG:<size>

/LOG must be used together with /EXT and <size> must be the same for both switches. Furthermore, <size> must be smaller or equal to free space.

/LOGO
Create logical drive with FAT16/FAT32 override

Works as /LOG.

/FPRMT
Prompt for FAT32/FAT16 in interactive mode

With /FPRMT you won't get the FDISK startscreen where you are asked for support for large disks. Instead, you will be prompted for FAT16/FAT32 each time you create a partition.

FDISK /FPRMT

/X
Do not use LBA partitions

With /X you won't get any LBA partitions.

FDISK /X

/CMBR
Recreate Master Boot Record on specified disk

Works as /MBR with the exception that you specify the disk to have it's MBR recreated.

FDISK /CMBR <disk>

Notes on /PRI, /PRIO and /LOG, /LOGO
As far as I can tell, PRI and LOG creates FAT32 when partitions are larger than 512Mb and FAT16 when partitions are smaller than 512Mb. PRIO and LOGO creates FAT16 even if partitions are larger than 512Mb (in effect, it’s like FDISK from DOS 5/6).