How to add processors to a computer that is running Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, Windows Vista, Windows 7 or Windows XP Professional x64 Edition

This article discusses how to add more processors to a computer that is running Microsoft Windows Operating System listed in Applies To section. 

The following list contains information about the number of processors that are supported in the various versions of Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, Windows Vista, Windows 7 and in Windows XP Professional x64 Edition:   


To add more processors to a computer that has only one processor, the following conditions must be true:

• The computer has a motherboard that can support multiple processors.
• The processors that you want to add to the computer use the same speed and the same stepping.
• Any BIOS updates or driver updates to the motherboard that you want to apply are installed on the computer before you add the additional processors.

Note Before you add a processor to the computer, make sure that the computer is turned off.

If these conditions are true, you can add the processor or processors. When you restart the computer, Plug and Play detects and installs the processor or processors.

All versions of Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, Windows Vista, Windows 7 and of Windows XP Professional x64 Edition use the Advanced Configuration and Power Interface (ACPI) Advanced Programmable Interrupt Controller (APIC) hardware abstraction layer (HAL).

Note The HAL option in Device Manager may change from ACPI APIC Uniprocessor HAL to ACPI APIC Multiprocessor HAL. This change does not indicate a change in HAL type. Instead, this indicates a change in the kernel.

After you add an additional processor to the computer, the computer detects the processor the next time that you start the computer. If the processor is not detected when you restart the computer, you must investigate possible hardware issues. For example, the processor may not be detected if one or more of the following conditions are true:

• The processor is incorrectly seated.
• The processor is damaged.
• The motherboard does not support the processor.
• The operating system is already supporting its maximum number of processors.

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: