Micro Firmware Tech Support

Notes on DOS FDISK Command


Filename: FDISK.TXT
WWW URL:  http://www.firmware.com/support/bios/fdisk.htm
FTP URL:  ftp://ftp.firmware.com/text/fdisk.txt
Author:   Terry Slade, Micro Firmware Technical Support
Revision: 04/22/99
Summary:  Some information on DOS FDISK program including differences
          in different versions of MS-DOS and Windows 95/98. 
FDISK is the utility provided with all versions of MS-DOS and Windows
95/98 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 - Basically the same as DOS 4.x, but now handles up to
8 physical drives

MS-DOS 6.x - Basically the same as DOS 5.x

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 the first drive (drive 1) can be made active. Only the first drive (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 partitions can be defined.

FDISK /MBR is an undocumented parameter that will create a new Master Boot Record.

FDISK does not automatically 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 5.00 and 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.

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).

A Quantum 12GB drive shows up like this on screen 4: (Partition has been previously defined with WIN95 FDISK)


Current Fixed Disk Drive: 1


Partition Status Type Volume Label Mbytes System Usage
C: 1 A PRI DOS 1149 7 100
%

Instead of like this:


Partition Status Type Volume Label Mbytes System Usage
C: 1 A PRI DOS 11497 100%

WIN95/WIN95A FDISK

Does support drives over 8.4GB, but is still limited to 2GB partitions. 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. Quantum 12GB shows just like example above (Option 4 (Display partition information) shows 12GB drive as "Total disk space is 1149 Mbytes" instead of "Total disk space is 11497 Mbytes"

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 gigbytes).
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 did show 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 may be a network drive.



Some Example Screen Dumps From DOS 6.22 FDISK



MS-DOS Version 6
Fixed Disk Setup Program
(C)Copyright Microsoft Corp. 1983 - 1993


FDISK Options

Current fixed disk drive: 1

Choose one of the following:

1. Create DOS partition or Logical DOS Drive
2. Set active partition * (Does not disturb data on drive)
3. Delete partition or Logical DOS Drive
4. Display partition information
5. Change current fixed disk drive * (If only one drive is present,
this option does not appear)
Enter choice: [1]

Press Esc to exit FDISK


Option 1 from main menu:

Create DOS Partition or Logical DOS Drive

Current fixed disk drive: 2

Choose one of the following:

1. Create Primary DOS Partition
2. Create Extended DOS Partition
3. Create Logical DOS Drive(s) in the Extended DOS Partition


Enter choice: [1]

Press Esc to return to FDISK Options
Option 2 from main menu:

Set Active Partition

Current fixed disk drive: 2

Only partitions on Drive 1 can be made active.

Press Esc to continue

Option 3 from main menu:

Delete DOS Partition or Logical DOS Drive

Current fixed disk drive: 2

Choose one of the following:

1. Delete Primary DOS Partition
2. Delete Extended DOS Partition
3. Delete Logical DOS Drive(s) in the Extended DOS Partition
4. Delete Non-DOS Partition



Enter choice: [ ]

Press Esc to return to FDISK Options

Option 4 from main menu:

Display Partition Information

Current fixed disk drive: 1

Partition Status Type Volume Label Mbytes System Usage
C: 1 A PRI DOS DRIVE C 244 FAT16 100%

* (A under Status indicates Active partition)

Total disk space is 244 Mbytes (1 Mbyte = 1048576 bytes)

Press Esc to continue
Option 4 - second drive (non-active)


Display Partition Information

Current fixed disk drive: 2

Partition Status Type Volume Label Mbytes System Usage
D: 1 PRI DOS DRIVE D 43 FAT16 100%


Total disk space is 43 Mbytes (1 Mbyte = 1048576 bytes)

Press Esc to continue


Option 5 from main menu:


Change Current Fixed Disk Drive

Disk Drv Mbytes Free Usage
1 244 0 100%
C: 244
2 43 0 100%
D: 43

(1 MByte = 1048576 bytes)
Enter Fixed Disk Drive Number (1-2).......................[1]


Press Esc to return to FDISK Options



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