FDISK.EXE HIDDEN PARAMETERS
- BACKUP ALL YOUR DATA TO A SAFE LOCATION FIRST!
- Use ALL FDISK.EXE command line switches with CAUTION, ONLY from native/real MS-DOS mode, NOT from a Windows DOS box/session, even full screen!
- FDISK /FPRMT [Windows 95B OSR2 + MS-DOS 7.10 and above ONLY]
FDISK /FPRMT bypasses the FDISK startup screen, but enables interactive FAT16/FAT32 support. This can be used to force FDISK to create FAT32 partitions smaller than 512 MB, normally not possible by default.
- FDISK x /PRI:n (/PRIO:n) /EXT:n /LOG:n (/LOGO:n) [MS-DOS 6.00 and above ONLY]
FDISK x /PRI:n (or /PRIO:n) /EXT:n /LOG:n (or /LOGO:n) MUST be used together for proper operation. Meaning:
If using FAT16 maximum size allowed is 2,047 MB (2 GigaBytes).
- x = drive number: 1, 2, 3... etc. Drive 1 corresponds to the 1st hard disk installed (C), drive 2 to second hard disk (D)... etc.
- /PRI:n = creates a primary partition of size n (in MegaBytes) and makes it bootable (active).
- /PRIO:n = creates a primary partition of size n (in MegaBytes) and makes it bootable (active) while overriding FAT16/FAT32.
- /EXT:n = creates an extended partition of size n (in MegaBytes) which holds logical partition(s).
- /LOG:n = creates a logical drive in the extended partition of size n (in MegaBytes).
- /LOGO:n = creates a logical drive in the extended partition of size n (in MegaBytes) while overriding FAT16/FAT32.
If using FAT32 maximum size allowed is 2,047 GB (2 TeraBytes).
- Maximum partition size MUST be equal to or smaller than existing free disk space.
- /EXT:n and /LOG:n (or /LOGO:n) partition sizes MUST be identical.
- Only one FDISK "LOG" is allowed per EACH logical drive! Therefore on computers with more than one logical drive you MUST run a separate FDISK x /LOG:n (or /LOGO:n) command for EACH installed drive.
- ONLY IF using Windows 95B OSR 2.0 + MS-DOS 7.10 or newer: /PRI:n and /LOG:n default to FAT32 on partitions larger than 512 MB, or to FAT16 on partitions smaller than 512 MB. /PRIO:n and /LOGO:n default to FAT16 even on partitions larger than 512 MB, same as older MS-DOS 5.00/6.xx FDISK.
- ONLY Windows 95B/95C OSR 2.x, 98, 98 SE(U), 2000, ME, XP and 2003 support FAT32.
- Use /LOGO:n instead of /LOG:n and/or /PRIO:n instead of /PRI:n to ignore FAT information in case of disk access errors.
- FDISK /MBR [MS-DOS 6.00 and above ONLY]
FDISK /MBR recreates the boot sector of the first (bootable) hard disk overwriting it with a fresh copy, by writing a new Master Boot Record (MBR) based on existent disk structure, without altering the partition table information.
Can be used to repair a damaged/corrupted MBR (i.e. by a virus).
WARNING: Writing the master boot record to the hard disk in this manner can render certain hard disks partitioned with SpeedStor unusable! It can also cause problems for some dual-boot programs (including Windows 95) or for disks with more than 4 partitions!
DEFINITION of MBR:
During the bootup sequence, at the end of the ROM BIOS bootstrap routine, the BIOS will read and execute the first physical sector of the first available floppy or hard drive on the system. This sector is called the Master Boot Record (MBR), or Master Boot Block (MBB), or Partition Table.
A small program is stored at the beginning of this sector and the partition table is stored at the end of this sector. This program uses the available partition information to determine which partition is bootable (usually the first primary DOS/WIN partition) and attempts to boot from it.
NOTE: The largest partition MS-DOS beginning with release 5.00 and up to Windows 95a OSR1 versions of FDISK can create/recognize is 2 GB (GigaBytes).
The 2 GB partition limit has been overcome by Microsoft (FINALLY!), beginning with Windows 95B OSR 2.0. Named the FAT32 file system, it supports partitions/drives up to 2 TB (TeraBytes).
Windows NT4/2000/XP/2003 have their own 32-bit protected file system called NTFS, INCOMPATIBLE with FAT32 or FAT16!
WINDOWS 95 AND 95a OSR1 "MBR REFRESH" BUG
There is a problem when installing a new hard drive on your system under Windows 95 [original retail] or 95a OSR1 [upgraded with SP1].
If you upgraded from MS-DOS 5.00 (or earlier), your primary hard disk, formatted under your old version of MS-DOS, contains the MBR (the Master Boot Record, also called the boot sector) written by the hard disk formatting utility (FDISK) provided with MS-DOS. When you add another hard disk under Win95, you format and partition it with the Win95/OSR1 (MS-DOS 7.00) version of FDISK.
This means that each drive was formatted and partitioned under a different OS, but Windows 95/OSR1 WON'T RECOGNIZE YOUR DRIVE! There is nothing wrong, don't panic. :) It's "just" another glitch in the OS, something Microsoft overlooked! :(
When a drive is formatted/partitioned under Win95/OSR1 the MBR tells the OS that the drive is a Windows (WIN) drive. If your drive was formatted/partitioned under earlier versions of MS-DOS (3.0 - 6.22) the drive is recognized as an MS-DOS (DOS) drive.
All you have to do is refresh the MBR by running FDISK (the Windows 95/95a OSR1 version) with the UNDOCUMENTED /MBR switch on the old drive, which repairs the boot sector by overwriting it with a fresh copy:
The boot record (MBR) will be refreshed without reformatting the drive or losing any data!
I presumed your primary (old) hard disk has assigned the letter C (single logical partition) and your new (secondary) hard disk is D (also with a single logical partition). Change drive letters if different on your system and/or if you have more than 1 partition per each hard disk.
This can be done ONLY from native/real MS-DOS mode AFTER you EXIT Win95/OSR1 GUI to MS-DOS or (re)BOOT with the "Command prompt only" option from the Startup Menu.
If the Win95 OS doesn't recognize the new drive, then you can ONLY do this after rebooting into your old MS-DOS version, using the dual-boot feature implemented into Win95 OS. This means you MUST have kept your old MS-DOS files (including FDISK) on your primary (old) hard disk.
You also need to have kept the old drive as primary (master) and set the new one as secondary (slave).
Reboot when done. Your (newly installed) hard drive should be recognized by the OS from now on.
Now you can change the new drive to "master" (primary boot drive) and setup the old one as "slave", especially if the new one is faster.
Sounds pretty complicated, but you may have to do this some day, and it's better than reformatting the entire drive, and losing precious data.
There is still another way to refresh/fix the MBR: run the Windows Scandisk tool (Scandskw.exe, located in your main Windows folder) on ALL hard drives on your system. It will automatically refresh the MBR (as needed) if it is damaged.
A MUST: Install Microsoft Windows 95 and 95a OSR1 LBA and INT13 IDE Hard Disk Data Loss DISKTSD.VXD Fix:
DSKTSUPD.EXE [147 KB].
NOTE: The "MBR BUG" does NOT affect Windows 95B/95C OSR 2.x, 98/98 SE(U) or ME.
FYI: Partition Magic overcomes the above Windows 95/OSR1 limitation, and makes ANY hard drive compatible with ANY Microsoft operating system and ANY FAT system (and much more). Retails for $30-60 at most computer stores. IMHO it's worth every penny, it saved my "computing life" more than once! :)
Supports Windows 95B/95C OSR 2.x/98/98 SE(U)/ME FAT32/FAT32X and NT4/2000/XP/2003 NTFS/NTFS5 file system standards.
- FDISK /Q [MS-DOS 6.00 and above ONLY]
FDISK /Q prevents rebooting the computer automatically after altering the partition information by using FDISK with other parameters.
- FDISK /STATUS [MS-DOS 5.00 and above ONLY]
FDISK /STATUS displays a screen similar to using FDISK's option 4: "Partition information", but shows also extended partition information (if any).
- FDISK /X [Windows 95 + MS-DOS 7.00 and above ONLY]
FDISK /X limits disk access to a total of 8.4 GB even on larger physical drives, even if the BIOS supports INT13h extensions for hard disks over 8.4 GB, thus preventing the use of 0E and 0F partition types, by ignoring LBA (Logical Block Addressing) and extended disk information.
This makes possible disk partitioning on computers with older BIOSes without support for hard disks larger than 8.4 GB.
Use /X to start FDISK if you receive disk access, stack overflow and/or data corruption error messages.
- FDISK /ACTOK [Windows 95B OSR 2.0 + MS-DOS 7.10 and above ONLY]
FDISK /ACTOK (ACT OK = act as if disk is OK) allows to set an active partition on any hard disk (if present) other than hard disk 0 (default = 128).
[Thank you JW Rebel!]
- FDISK /CMBR x [Windows 95B OSR 2.0 + MS-DOS 7.10 and above ONLY]
FDISK /CMBR x MUST be used together for proper operation. Recreates the boot sector of the second, third... etc hard disk(s) (if any) overwriting it (them) with a fresh copy, by writing a new Master Boot Record (MBR) based on existent disk structure, without altering the partition table information. Valid values for x:
Can be used to repair a damaged/corrupted MBR (i.e. by a virus).
- 1 = first (bootable) physical hard disk (same as using FDISK /MBR):
FDISK /CMBR 1
- 2 = second (not bootable) physical hard disk (if any):
FDISK /CMBR 2
- 3 = third (not bootable) physical hard disk (if any):
FDISK /CMBR 3
- ... etc.
- FDISK /PARTN [MS-DOS 6.00 ONLY]
FDISK /PARTN saves the partition information to a plain text file called PARTSAV.FIL, which can be viewed afterwards using any text editor/viewer, like EDIT.COM in DOS or Notepad in Windows.
- FDISK /PRMT [MS-DOS 6.00 ONLY]
FDISK /PRMT adds extra prompt ["nagging" :)] screens which require user input (key press) before proceeding further.
BACK 2 CONTENTS