Microsoft KB Archive/252326

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Windows 2000 Setup Detects Only One CPU on Some Compaq Servers

Article ID: 252326

Article Last Modified on 2/28/2007


  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server

This article was previously published under Q252326


When you install Windows 2000 on a Compaq computer that supports multiple processors (such as the Compaq Proliant 3000, 5500, 6400, 6500, and 1850R) with multiple processors on board, Setup may detect only one processor (CPU).


Compaq Proliant multiple-processor computers have a Complimentary Metal-Oxide Semiconductor (CMOS) setting that specifies the operating system. If this setting is set to Other, Setup detects only one processor. This occurs because the Advanced Configuration and Power Interface (ACPI) setting is disabled. Compaq SMP-based servers require that the appropriate operating system is configured in CMOS to see all processors correctly.


To work around this issue and allow Windows 2000 to detect all processors in the computer, use any of the following methods:

  • Using Compaq System Configuration Utility 2.48a or later, change the setting that specifies the operating system to Windows 2000. Some earlier versions of System Configuration Utility do not have a Windows 2000 option, so be sure to use version 2.48a or later.
  • Change the ACPI mode from Disabled to Full Tabled Mapped or Full Table. To determine which mode to use, please contact Compaq Computer Corporation for details.

NOTE: To access the ACPI setting, Advanced mode must be enabled in System Configuration Utility. To enable this mode, press CTRL+A at the System Configuration Utility main menu.

You should also install the latest BIOS to enable new features that are used in Windows 2000, such as ACPI support. You can find all the updated files and drivers needed for Windows 2000 at the Compaq download support site:

After you configure the settings described in this article, you can install the multiple-processor hardware abstraction layer (the MPS HAL), in Device Manager to cause Windows 2000 to detect all the processors only if going from non-ACPI-UniProcessor HAL to non-ACPI-MultiProcessor or when going from ACPI-Uniprocessor HAL to ACPI-MultiProcessor HAL. For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base:

237556 Troubleshooting Windows 2000 Hardware Abstraction Layer Issues

234558 HOW TO: Add Support for Multiple Processors in Windows 2000

NOTE: You can use this procedure only to upgrade from a single-processor HAL to a multiple-processor HAL. If you use this procedure to change from a standard HAL to an ACPI HAL (for example, after a BIOS upgrade) or vice-versa, unexpected results may occur, including an inability to start the computer.

The third-party products that are discussed in this article are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.

Additional query words: uptomp

Keywords: kbenv kbhardware kbprb kbsetup KB252326