Programs become unstable or do not start after you install an x64-based version of Windows on the same partition as a 32-bit version of Windows

After you install an x64-based version of Microsoft Windows on a computer that also has a 32-bit version of Windows installed, you may experience the following symptoms:

• Some of your programs become unstable.
• You cannot start the 32-bit version of Windows.
• The files in the Program Files folder are replaced with 64-bit versions of these files. Therefore, the Program Files folder contains a mixture of 32-bit and 64-bit files.

These issues occur if you install an x64-based version of Windows on the same partition as your 32-bit version of Windows. Dual-boot environments are not supported if the 32-bit version of Windows and the x64-based version of Windows are installed on the same partition.

To resolve these issues, reinstall the x64-based version of Windows and the 32-bit version of Windows on separate partitions. Make sure that you back up all important data before you do this.

Dual-boot configurations that include an x64-based version of Windows and a 32-bit version of Windows are fully supported by Microsoft. However these operating systems must reside on separate drive partitions. In a dual-boot environment, you can run 16-bit programs on a 32-bit version of Windows. The 32-bit version of Windows also provides support for programs that use a 16-bit Setup program. However, programs that use a 16-bit Setup program are not supported in x64-based versions of Windows.

When you try to install an x64-based version of Windows on a partition that already contains a 32-bit version of Windows, the following warning appears in the text-mode Setup program:If you want to set up a dual-boot system, use the following best practices:

• Always install the 32-bit version of Windows first to make sure that the correct startup files are written to the root of the drive. If you overwrite the x64-based version of NT Loader (NTLDR) with the version of NTLDR that is included with 32-bit versions of Windows, this prevents the x64-based version of Windows from starting. The version of NTLDR that is included with x64-based versions of Windows is backward-compatible with the version of NTLDR that is included with 32-bit versions of Windows. The versions of NTLDR that are included with the 32-bit versions of Microsoft Windows XP and Microsoft Windows Server 2003 cannot start the current releases of x64-based versions of Windows.
• Do not install an x64-based version of Windows on the same partition as a 32-bit Windows installation. The x64-based versions of Windows use the same Program Files folder and the same Documents and Settings folder as 32-bit versions of Windows. Therefore, the contents of these directories may be replaced with 64-bit versions of the .dll and .exe files that are required by the 32-bit versions of Windows. If the 32-bit files are replaced, 32-bit programs and services may not start or may become unstable. If you unintentionally install the x64-based version of Windows on the same partition as an existing 32-bit version of Windows, back up as much data as possible. Then, format and reinstall both operating systems.

Technical support for Windows x64 editions

Your hardware manufacturer provides technical support and assistance for Microsoft Windows x64 editions. Your hardware manufacturer provides support because a Windows x64 edition was included with your hardware. Your hardware manufacturer might have customized the Windows x64 edition installation with unique components. Unique components might include specific device drivers or might include optional settings to maximize the performance of the hardware. Microsoft will provide reasonable-effort assistance if you need technical help with your Windows x64 edition. However, you might have to contact your manufacturer directly. Your manufacturer is best qualified to support the software that your manufacturer installed on the hardware.

For product information about Microsoft Windows XP Professional x64 Edition, visit the following Microsoft Web site: For product information about Microsoft Windows Server 2003 x64 editions, visit the following Microsoft Web site: