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Install MS-DOS on a Window XP or 2000 that uses FAT32

Last reviewed: September 2008

On this page:
• About adding MS-DOS 7.10 to Windows XP/2K
• How it works
• Preparation: Dual-Boot MS-DOS 7.10 on a Windows XP/2000 that uses FAT32
• Procedure: Installing MS-DOS on a Windows XP or 2000 that's using FAT32
• How to return to your original Windows-only system
• Boot Disks & your own Rescue Boot Disk

About adding MS-DOS 7.10 to a Windows XP/2K that uses FAT32

You can install MS-DOS 7.0+ on a computer with a FAT32 Windows XP or 2000 already installed so you can select either MS-DOS or Windows on startup (a dual-boot is created). There will be no loss of data and no commercial utilities are required.

There is no need to create another drive (partition) because both operating systems can safely use the same partition, the C: drive. The version of MS-DOS must be FAT32-capable. This page will use the MS-DOS version 7.10 used by Windows 98SE. The single hard disk used in testing was a 40 GB Western Digital all of which was used by Windows on a single FAT32 partition. The Windows systems used were Windows XP Professional (SP2) and Windows XP Home Edition (version 2002, SP1) and Windows 2000 (5.00.2195, Service Pack 5).

The procedure described here will also work when you already have a Windows-controlled (NTLDR) dual-boot provided the first FAT32 partition is a Primary partition, is the Active partition, and contains the boot files (Boot.ini, NTLDR, and Ntdetect.com - all hidden files).

You must not use this page if your current Windows uses NTFS. Use the instructions in Install MS-DOS 7.10 on a Window XP or 2000 that uses NTFS- there are substantial differences in the procedures.

How it works

When a Windows XP or 2000 is installed on a computer that already contains only a MS-DOS installation, the following occurs automatically during the installation of Windows XP/2000.
1. The existing MS-DOS boot sector is saved to C:\Bootsect.dos.
2. The existing MS-DOS boot sector is over-written by the Windows XP/2000 version.
3. A line to call the MS-DOS boot sector in C:\Bootsect.dos is entered into C:\Boot.ini.
A dual-boot of the two operating systems has been created by just installing a newer Microsoft operating system.

To install the older MS-DOS on a computer that already contains a newer Windows installation, we must do the equivalent manually.
1. First create a MS-DOS boot sector on C:, copy it to C:\Bootsect.dos, and copy MS-DOS boot files to C:
2. Over-write the MS-DOS boot sector with one for Windows XP/2000.
3. In C:\Boot.ini, enter a boot option that calls the MS-DOS boot sector saved in Bootsect.dos.

The SYS C: command in Btsect (btsect25.zip) creates the MS-DOS boot sector on C: and also copies Command.com, Drvspace.bin, Io.sys, and Msdos.sys to C:. Btsect then copies the MS-DOS boot sector of C: to C:\Bootsect.dos. Fixboot, run from the Recovery Console, writes a Windows XP/2000 boot sector on C: (returns the sector to its original state).

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Preparation: Dual-Boot MS-DOS 7.10 on a Windows XP or 2000 that uses FAT32

  1. It's routine to backup important data first.
     
  2. You need your Windows XP/2000 CD (full installation version - a restore or recovery CD may not work).
    If already dual-booted, you need the CD for the most recent version of Windows.
    You also need the Administrator password if one was set - it's rarely set in home computers.
     
  3. Read Create a new BOOTSECT.DOS and download THPC's btsect25.zip (7 KB). Extract its three files (18 KB) to a Windows 98/98SE Startup Disk. Choice.com (6 KB) must always be added to this floppy (same version please!).

    If using an ordinary MS-DOS boot floppy/CD, the following files must be on the floppy:
    attrib.exe (15 KB), choice.com (6 KB), debug.exe (21 KB), sys.com (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 Bootdisk.com.
     
  4. Create a C:\dos71 as a storage folder for DOS files and remember, later on, to enter that location in Autoexec.bat's PATH.
     
  5. This might be a good time to run Disk Defragmenter, and run Chkdsk /F from a Command Prompt. Allow plenty of time!

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Procedure: Installing MS-DOS on a Windows XP or 2000 that's using FAT32

Reboots are important. Please follow on-screen instructions.

  1. Prepare (read above)

    First make a MS-DOS boot sector on C: and copy it
  2. Boot from the Win98/SE boot floppy/CD.
        Run A:\btsect and allow the SYS C: command to run
        - you must use the SYS C: option to create the MS-DOS boot sector.
        The MS-DOS boot sector will be created on C: and then copied to C:\Bootsect.dos,
        and Command.com, Drvspace.bin, Io.sys, and Msdos.sys will be copied to C:
        Install your full MS-DOS now or later. Use the C:\dos71 folder except for boot files.
    Reboot (remove floppy). Only MS-DOS boots at this stage.

    Recreate the Windows XP/2000 boot sector on C:
  3. Boot from your Windows installation CD.
        Press R to enter the Recovery Console (and then C for Windows 2000).
        Logon
        At the prompt, type (and press Y to confirm when requested):
        fixboot
        exit
    Reboot (remove CD). Only Windows XP/2000 boots at this stage.

    Finally, edit Boot.ini so MS-DOS can be selected during startup
  4. Edit Boot.ini (it's a Read-only, Hidden, file in 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:
    Reboot.

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

If you did not install all the MS-DOS files earlier, you must now copy them to the hard disk. Actually installing MS-DOS at this stage would rewrite the boot sector just like SYS C: does!

* 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.
Reboot! Windows boots automatically without the appearance of a boot loader screen.

Delete the DOS71 and Bootsbck folders, and any other folders created for use with MS-DOS only.

To fully complete removal, delete the unrequired boot files on the root of the C: drive:
Autoexec.bat, Bootsect.dos, Command.com, Config.sys, Drvspace.bin, Io.sys, and Msdos.sys

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BOOT DISKS & YOUR OWN RESCUE BOOT DISK

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, Ntdetect.com, 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
   Use RDISK.EXE /S
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 Bootdisk.com (IDE CDrom Drivers Included).

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