This article describes preventive steps that you can take to preserve data before you attempt to remove Windows XP and install Windows NT 4.0 on your computer.

Removing Windows XP and installing Microsoft Windows NT 4.0 is a manual process; no uninstall process is available.

Note that this article does not describe how to install Windows NT 4.0. For information about how to install Windows NT 4.0, refer to the product manuals and the Microsoft Knowledge Base.

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The easiest way to remove Windows XP from your computer and reinstall Windows NT 4.0 is to back up any data and files that you need to keep, reformat and repartition all drives, install Windows NT 4.0, install the latest Windows NT 4.0 service pack, install your programs, and then restore your data.

If the size of the boot drive, the system drive, or both exceeds 7.8 gigabytes (GB), you need to repartition the drive because of a limitation in Windows NT 4.0 Setup. Also, you need to remove or reformat any drives that are formatted with the FAT32 file system.

For additional information about these issues, click the article numbers below to view the articles in the Microsoft Knowledge Base: Before you remove Windows XP from your computer, review the following topics:

•	Backing Up Data
•	Reformatting NTFS Drives
•	Reformatting FAT32 Partitions
•	Backing Up Encrypted Files
•	Backing Up Profiles
•	Overwriting the Boot Sector
•	Deleting Files and Folders
•	Converting Dynamic Disks

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Backing Up Data

Before you remove or install an operating system, back up all data files that are in the computer to prevent accidental file deletions. Backup is particularly important if you have FAT32-formatted partitions, because these partitions are not available under Windows NT 4.0. Also, there are some NTFS file system limitations after you upgrade your computer to Windows XP.

Copy all data files to a network share or to removable media, or back them up by using a backup program that is compatible with both Windows XP and Windows NT 4.0. After you reinstall Windows NT 4.0, the latest service pack, and any programs, you can restore the data.

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

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Reformatting NTFS Drives

When you install Windows XP, all NTFS volumes on your computer are upgraded to the version of NTFS that is included with Windows XP. Although Windows NT 4.0 Service Pack 4 (SP4) or later enables read and write access to these drives, there are some limitations:

•	Utilities such as Chkdsk that are included with Windows NT 4.0 do not work properly.
•	Access to the Repair and Chkdsk utilities that are included with Windows XP is possible only while you are running one of the two operating systems or when you are running Recovery Console for one of the two operating systems.
•	Some enhanced features such as Encryption or Reparse Points are not available, and files that are encrypted or that contain reparse points are not accessible under Windows NT 4.0.

For these reasons, Microsoft recommends that you back up all data and then reformat these NTFS drives either during Setup or after you install Windows NT 4.0.

NOTE: Because of upgrades that Windows XP performs on all NTFS drives, you cannot use Windows NT Setup to set up boot and system drives that are formatted with NTFS. Although the driver in Windows NT 4.0 SP4 or later enables you to read and write to NTFS drives, there is no way to place this driver into the Windows NT 4.0 Setup process. Because of this, the NTFS driver in Windows NT 4.0 is not able to properly read or write from NTFS drives that are upgraded by Windows XP. There is no workaround to this issue. Note that NTFS data drives become available under Windows NT 4.0 after you install Service Pack 4 or later.

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Reformatting FAT32 Partitions

Windows XP supports the FAT32 file system, but Windows NT 4.0 does not. FAT32-formatted partitions are not available under Windows NT 4.0, and data on these partitions is not accessible unless you are dual-booting with an operating system that does support FAT32 (for example, Microsoft Windows 98).

The system drive is the drive that contains the boot files, and the boot drive is the drive that contains the Winnt folder; these drives cannot be a FAT32-formatted partition. Back up all data that is located in FAT32 partitions, and then format the partitions with either FAT or NTFS. You can do this either during Windows NT 4.0 Setup or later. Note that NTFS-formatted drives must be reformatted as NTFS under Windows NT 4.0.

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Backing Up Encrypted Files

Windows XP supports the encrypting of files on NTFS drives, but Windows NT 4.0 does not. Files that are encrypted under Windows XP are not available under Windows NT 4.0. You must decrypt these files before you back them up so that they are available after you reinstall Windows NT 4.0.

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Backing Up Profiles

By default, Windows NT 4.0 and Windows XP do not store profiles in the same location. The default location for profiles in Windows NT 4.0 is the %SystemRoot%\Profiles folder. The default location for profiles In Windows XP is the %SystemDrive%\Documents and Settings folder, but if you upgraded from Windows NT 4.0, the profiles are still in the %SystemRoot%\Profiles folder.

Profiles usually contain some data files and may contain other necessary information. Deleting the %SystemRoot% folder when you remove files can delete the data that is in the profiles. Because of this, it is important that you back up these files first.

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Overwriting the Boot Sector

If you do not repartition or reformat the system drive, and you do not install Windows NT 4.0, the boot sector may still be on the drive. This is not an issue if the drive is formatted with the FAT file system. If you reinstall Windows NT 4.0, the Windows XP boot sector may be overwritten. If the Windows XP boot sector is not overwritten, you can run the Windows NT 4.0 Repair process and choose to overwrite the boot sector.

In most cases, Microsoft recommends that you first start the computer by using a Windows 98 or Microsoft Windows 95 Startup disk, and then run the sys command on the drive before you run a Repair process or install Windows NT 4.0.

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Converting Dynamic Disks

Windows XP supports dynamic disks, but Windows NT 4.0 does not support dynamic disks. Unless you convert dynamic disks to basic disks before you remove Windows XP and install Windows NT 4.0, the disks will not be available under Windows NT 4.0.

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Deleting Files and Folders

There are several files and folders that you must delete. (If you repartition or reformat the drives, some of these files and folders are not present.) You must delete some files from the system drive (the drive that the computer boots from), and you must delete some folders and files from the boot drive (the drive that contains the %SystemRoot% folder, which is usually the Winnt folder). The system drive and the boot drive may be in the same location, or they may be on separate volumes.

Before you delete any folders, verify that you have a good backup of any files that you want to have available after you reinstall Windows NT 4.0. After you delete these files, Windows XP is unavailable. You must have the Boot.ini, Ntldr, and Ntdetect.com files from Windows NT 4.0 to boot Windows NT 4.0.

Files on the System Drive

Folders and Files on the Boot Drive

SystemRoot folder
(in which Windows XP is currently installed, by default the Winnt folder)

Program Files folder

Documents and Settings folder
(unless you upgraded to Windows XP from Windows NT 4.0)

Pagefile.sys
Hiberfil.sys
(if hibernation was enabled on the computer)

It is recommended that you install Windows NT 4.0 in its own partition, not in a partition that contains an installation of Windows XP. However, in some cases, this may not be possible, or restoring Windows NT 4.0 on the computer may be time critical. If you have only one partition available, and if this partition has enough disk space for the installation, use the following procedure:

1.	Start Windows NT 4.0 Setup by using the Winnt32.exe program that is included with Windows NT 4.0 SP4 or later. If this program is not available, start your computer by using a Windows 95 or Windows 98 Startup disk, and then type sys c:, where c is the drive that you boot from. If you experience a reboot loop (because of a problem with the Windows NT 4.0 Setup program if Windows XP was installed), either remove the Windows XP boot sector and replace it with an MS-DOS-based boot sector, or use the Winnt32.exe program that is included with SP4 or later.
2.	If you install Windows NT 4.0 in a folder other than the Winnt folder, you do not need to rename the Winnt folder. However, if you want to use the same folder name, you must rename the existing Winnt folder. For example, type ren winnt winXP at a command prompt, and then press ENTER. This command renames the Winnt folder to "WinXP". Note that after you do this, you cannot reuse Windows XP.
3.	At a command prompt, to rename the Program Files folder, type the following command, and then press ENTER: ren "program files" "old program files" Because both Windows NT 4.0 and Windows XP use the Program Files folder, you must rename this folder if you are installing Windows NT 4.0 on the same drive and you do not want to delete the folders at this time. If the Hiberfil.sys file exists, you can delete it; this file is not used in Windows NT 4.0.
4.	The Documents and Settings folder is not used by Windows NT 4.0 and is not overwritten. It will be available after the upgrade unless you format or partition the drive during Windows NT 4.0 setup.

After you rename the two folders and replace the boot sector with one from the Windows 95 or Windows 98 Startup disk, you can install Windows NT 4.0. You should have the three Windows NT 4.0 boot floppy disks to start Windows NT 4.0 Setup. If not, you can boot by using a Windows 98 Startup disk or a bootable disk that contains your CD-ROM drivers, and then run Winnt.exe. This copies the files from the CD-ROM to the local hard disk and creates the three boot floppy disks.

NOTE: If you boot with a Windows 98 Startup disk, run Smartdrv to help speed up file copying.

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