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Install MS-DOS 7.10 on a Window NT that uses NTFS

Last reviewed: September 2008

On this page:
• About adding MS-DOS 7.10 to a Windows NT that uses NTFS
• How MS-DOS will work with NTFS
• Preparations: Dual-Boot MS-DOS 7.10 on a Windows NT that uses NTFS
• Procedure: Install MS-DOS 7.10 on a Windows NT that is using NTFS
• How to return to your original Windows-only system
• Boot Disks & your own Rescue Boot Disk

About adding MS-DOS 7.10 (FAT or FAT32) to a Windows NT that uses NTFS

You can install MS-DOS 7.10 on a computer with Windows NT using NTFS already installed so you can select either MS-DOS or Windows NT on startup (a dual-boot is created). There should be no loss of data and no commercial utilities are required.

However, you must create a new Primary partition (drive) at the end of the NTFS partition(s) for the MS-DOS installation. If you don't have free space (unallocated) at the end of the hard disk, you can resize (smaller) the existing partition with PartitionMagic (commercial), or with GParted (free, and just as good!) on the GParted Live CD (90 MB) or on Ubuntu Live CD (700 MB), or with a variety of other partitioning/resizing utilities. Unfortunately, the free Easeus Partition Manager Home Edition (8 MB) does not appear to work with Windows NT.

MS-DOS must be installed on a Primary FAT32/FAT partition on the first hard disk (seen as Disk0 at boot time).

You must not use this page if your current Windows uses the FAT file system. Use the instructions in Install MS-DOS on a Window NT that uses FAT - there are substantial differences in the procedures.

The MS-DOS version 7.10 that comes with Windows 98SE was used in testing. The single hard disk used was a 40 GB Western Digital all of which was used by Windows NT Workstation 4.0 (Build 1381, SP1 updated to SP6) on a single NTFS partition.

Initially Windows NT v4.0, SP1, was used successfully but proved unfriendly because of the disk size limitation (7.8 GB) and the NT installation partition size limitation. Thereafter, the SP1 was updated to SP6 before the procedure described here and this proved more satisfactory because the entire disk could be used from the very start.

How MS-DOS will work with NTFS

The Windows NT boot loader (NTLDR) will gladly boot to MS-DOS provided a few conditions are met.
1. MS-DOS is installed on a different Primary partition (FAT/FAT32) on the first hard disk (Disk0).
2. A copy of that partition's boot sector is in a file (Bootsect.dos) on the NT partition with the other NT boot files.
3. A line that locates Bootsect.dos is included in NT's Boot.ini file.

Unallocated free space is created at the end of the NTFS partition. FAT will be used if less than 2048 MB is allocated to MS-DOS; if greater than that, FAT32 can be used.

Fdisk (preferably) is used to create a Primary partition in the Unallocated space and that partition is Formatted with FAT32 or FAT. When booted to MS-DOS, any NTFS partition is ignored and the FAT or FAT32 Primary partition is automatically the C: drive.

The SYS C: command in Btsect ( creates a MS-DOS boot sector on this C: (it's the FAT/FAT32 drive) and also copies, Drvspace.bin, Io.sys, and Msdos.sys to C:. Btsect then copies the MS-DOS boot sector of C: to C:\Bootsect.dos.

The newly created Bootsect.dos must now be copied to the root of the NTFS partition that contains the NT boot files - the Active partition. This is not a problem if MS-DOS is on a FAT partition because Windows NT gives access to FAT partitions but not to FAT32. If Bootsect.dos is on a FAT32 partition, it must first be copied to a media accessible by Windows NT. This is usually a floppy disk or a hard disk FAT Logical partition - Bootsect.dos can be copied from there to the NTFS partition when booted to Windows NT.

Adding the line, c:\bootsect.dos=" dos ", to boot.ini completes the dual-boot creation.

The NTFS partition always remains the Active partition and Windows NT always retains its ability to boot throughout the process. MS-DOS will not be independently bootable at any stage (unless its partition is made Active!).

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Preparation: Dual-Boot MS-DOS 7.10 on a Windows NT that uses NTFS

  1. Optionally, update your Windows NT installation with Service Pack 6 (or 5) if you can or need to.
  2. It's routine to backup important data first.
  3. Download a partition manager that allows resizing of a partition (read above).
  4. Read Create a new BOOTSECT.DOS and download THPC's (7 KB). Extract its three files (18 KB) to a Windows 98/98SE Startup Disk. (6 KB) must always be added to this floppy (same version please!).

    If using an ordinary MS-DOS boot floppy/CD (or Win95 Startup Disk), the following files must be on the floppy:
    attrib.exe (15 KB), (6 KB), debug.exe (21 KB), (19 KB)

    If you don't have a floppy drive, you can use a bootable CD created from an ISO or IMA image of MS-DOS using a utility like CDBurnerXP (free) or Nero. There's plenty of MS-DOS images available free on the Web. Before you create the bootable CD, make sure the ISO file contains the three Btsect25 files, and also Attrib, Choice, Debug, Sys (the free WinImage, and similar utilities, allow you to add files to an .IMA image). Incidentally, in this dual-boot creation, do not allow a MS-DOS installation to write to the MBR (Master Boot Record).

    Booting MS-DOS from a USB flash drive is still a hit-or-miss affair. However, you might like to Google with 'boot usb flash pen stick drive' or have a look at How To Boot From A USB Flash Drive at
  5. This might be a good time to run Disk Defragmenter, and run Chkdsk /F from a Command Prompt. Allow plenty of time!
  6. Disable Virtual Memory ---> Start > Settings > Control Panel > System > Performance tab > Change button - set both Initial Size and Maximum Size to 0, and click the Set button (remove this unmovable hidden file that may prevent resizing of the hard disk).

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Procedure: Install MS-DOS 7.10 on a Windows NT that is using NTFS

Reboots are important. Please follow on-screen instructions.

  1. Prepare (read above)
  2. Create Unallocated free space at end of hard disk for MS-DOS (read above).
    Reboot to Windows when finished, let Chkdsk finish and reboot again if requested.
  3. Boot from Win98/SE boot floppy/CD. No FAT/FAT32 drive exists, so ignore the caution.
    Run Fdisk.
        Press Y for enable large disk support, if you intend using FAT32 for MS-DOS.
        Press Y for should NTFS partitions on all drives be treated as large (if it appears).
        Create a Primary partition - leave 16 MB unused if using FAT32 and you have no floppy.
        If you just left 16 MB unallocated, create an Extended and then a Logical partition there.
        Press ESC until you exit from Fdisk.
  4. Reboot from Win98/SE boot floppy/CD. C: is now the new Primary (DOS ignores NTFS).
        Format the new Primary (C:) with FAT32 or FAT - give it a doss label.
        Format the tiny Logical partition (D:) if you created it - give it a dummy label.

    Finalise all previous items before the executing next part.

        Run A:\>btsect   and press Y for the SYS C: option.
        (MS-DOS boot sector will be written to new Primary partition and copied there as a Bootsect.dos file - 512 bytes).
        Copy the new C:\Bootsect.dos to floppy or to FAT partition (attrib -r -h -s c:\bootsect.dos is required).
  5. Reboot. Only Windows NT boots at this stage. C: is now he NTFS drive.
        Let Chkdsk finish plus its reboot, and then reboot again after bootup if requested.
    Copy Bootsect.dos from the new FAT32/FAT drive to root of the C: drive.
    Edit Boot.ini (it's a Read-only, Hidden, file on root of C:) - you can read How to Edit Boot.ini
        Add the following line to the end of the [operating systems] section
        C:\BOOTSECT.DOS=" MS-DOS 7.10 "
        and, optionally, change the timeout under [boot loader] to timeout=10 (that's 10 seconds).
        Save Boot.ini back to C:
    Reset Virtual Memory if you disabled it earlier.

Finished! You now have a boot menu containing both operating systems.

Boot to 'MS-DOS 7.10' and install your full MS-DOS 7.10. Installing or re-installing MS-DOS from DOS at this stage will not rewrite the boot sector of the NTFS partition which is recognised by MS-DOS 7.10 but is then totally ignored.

When booted to Windows, you'll see a drive letter has been allocated to a FAT32 partition even though you can not use that drive. You must not delete this partition - it contains your MS-DOS!

* You must recreate and copy Bootsect.dos again if the hard disk geometry is altered again.

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How to return to your original Windows-only system

Remove the line C:\bootsect.dos=" MS-DOS 7.10 " from the Boot.ini file.

The only substantial change to your computer system has been the resizing and creation of the partition(s). The end of the disk is the safest area for such operations. Whenever you wish, you can reformat the MS-DOS partition with NTFS, or delete it and then resize the Windows partition to include that space.

To Format or Delete a partition, use Disk Administrator in Windows NT.
Use your own partition management utility to Resize (larger) a partition.

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NEVER dual-boot without your personal safety net - a BOOT DISK for XP/2K/NT.
If stuck, use a Win9x Startup Disk (CD support), and run WINNT.EXE from I386 folder on CD.

If you don't have a floppy drive, you should investigate how to create a bootable CD from a floppy disk image.

RESCUE BOOT DISK for when XP, 2K, NT will not boot - ESSENTIAL, 1 floppy
   Create a bootable floppy to get XP/2K/NT running even if the boot record,
   or boot files, are ever a problem. Write-protect and keep it safe.
      Format a floppy with that XP, 2K, or NT. It must be a full XP/2K/NT format.
      Alter file Attributes (Attrib -r -s -h) of these files in root of C: (PC system partition)
      Boot.ini, NTLDR,, and Bootsect.dos & Ntbootdd.sys (if present)
      (plus Arcldr.exe & Arcsetup.exe - for Windows 2K) and copy them to the floppy.
      Write-protect the floppy. Then restore original Attributes to the files on C:.
      Read the Rescue Boot Disk page for fuller details, plus a much improved Rescue disk.
Use the CD: If you have a Bootable installation CD you should check if your BIOS
   supports booting from it. This is hugely convenient, but still make the floppy.
ERD XP, 2K, NT: Emergency Repair Disk - repair key Registry entries and partition geometry
2K/NT Setup Boot Disks: (4 floppies for 2K, or 3 for NT)
   Use WINNT32 and MAKEBT32 from 2K/NT (\Boot disk folder on CD).
   Use WINNT and MAKEBOOT from a non-2K/NT system (such as Win9x).
XP Setup Boot Disks: (6 floppies)
   Read the Microsoft page How to obtain Windows XP Setup boot disks.
   It provides free downloads that create setup boot floppies for all versions of Windows XP.
   Each download is specific to each XP version (Home/Pro; original/SP1/SP2).
Win9x/Me Startup Disk:
   (95+) From a Windows: Control Panel > Add/Remove Programs > Startup Disk tab.
   (98+) From true MS-DOS: Go to the Command folder in Windows, and type Bootdisk.
   Windows 95 Startup Disks do not have CD support (add your CD-ROM driver).
   You can download free Win9x/Me boot disks from (IDE CDrom Drivers Included).

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Please remember that you alone are responsible for the consequences of any changes you make to your computer hardware or software.

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