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Undocumented FDISK | |
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| Background |
| This page describes undocumented switches you can use with FDISK. With
the switches you can use FDISK in non-interactive mode, e.g. in a batch
file.
The switches works with the FDISK that is include with Windows 95 OSR2 (MS-DOS 7.1). Several people has contributed to this page. If you have comments, suggestions or questions, feel free to send me an e-mail. |
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I haven't found a way to delete existing partitions with FDISK so I wrote a small utility, INSTHELP, to nuke the Partition Table. Use with care. |
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| How To Do |
Variables used in this document:
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| /STATUS | Show current partition layout | |
| /MBR | Recreate Master Boot Record on disk 1 | |
| /PRI | Create primary partition | |
| /PRIO | Create primary partition with FAT16/FAT32 override | |
| /EXT | Create extended partition | |
| /LOG | Create logical drive | |
| /LOGO | Create logical drive with FAT16/FAT32 override | |
| /FPRMT | Prompt for FAT32/FAT16 in interactive mode | |
| /Q | Skip forced reboot on exit Info provided by Mike Cowen and Paul Helsen | |
| /X | Do not use LBA partitions Info provided by Francisco Arráez Sánchez. | |
| /ACTOK | Do not check drive integrity Info provided by Svend Christensen. | |
| /CMBR | Recreate Master Boot Record on specified disk Info provided by Francisco Arráez Sánchez. | |
| Notes on /PRI, /PRIO and /LOG, /LOGO |
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| /STATUS - Show current partition layout
FDISK /STATUS |
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If you have an extended partition with no logical drive defined, no information about the extended partition is shown. |
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| /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 /MBR |
| /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> |
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If <size> is larger than the space on the HD all space is used for the primary partition. |
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| /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> |
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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. |
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| /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> |
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/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. |
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| /LOGO - Create logical drive with FAT16/FAT32
override
Works as /LOG. |
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| /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 promted for FAT16/FAT32 each time you create a partition. FDISK /FPRMT Additional info provided by Jeff Richards: Note that the prompt for FAT16/FAT32 will be available for ALL partitions, so this option can be used to force FDISK to create FAT 32 partitions smaller than 540Mb. (By default, FDISK uses FAT32 for partitions greater than 540Mb only). | |
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| /Q - Skip forced reboot on exit
With /Q the PC will not be rebooted after modifying the Partition Tables. However, I don't recall that DOS 7.x FDISK does a reboot. Maybe it's because I always use FDISK from a boot-floppy. FDISK /Q | |
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I have not tried this switch. Mike Cowen and Paul Helsen provided the information. |
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| /X - Do not use LBA partitions
With /X you won't get any LBA partitions. See Micro Firmware Technical Support for more details. FDISK /X |
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I have not tried this switch. Francisco Arráez Sánchez provided the information. |
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| /ACTOK -
Do not check drive integrity
With /ACTOK the integrity of drive is not checked making FDISK faster. FDISK /ACTOK NOTE: It may not work everytime - please let me know your experience with /ACTOK. | |
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I have not tried this switch. Svend Christensen provided the information. |
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| /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> | |
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I have not tried this switch. Francisco Arráez Sánchez provided the information. |
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| 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). |
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| Piping Keystrokes |
| You can pipe keystrokes into FDISK using a file which contains the
keystrokes including <CR>. Most editors can't
insert the <CR> character without <LF> so you need a
hex-editor to do the job. Take a look at CREATE.TXT and ERASE.TXT (download
them).
Example 1a - Create extended partition: FDISK < CREATE.TXT Example 1b - Create extended partition without drive-integrity checking: FDISK /ACTOK < CREATE.TXT Example 2 - Delete extended partition from example 1a/1b: FDISK < ERASE.TXT All the piping information was provided by Svend Christensen. |
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| Other Links |
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| DISCLAIMER: The use of FDISK and other programs as described in this document is entirely on your own risk. |
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| Updated 22 AUG 1999 by Michael Jacobsen. |