Different ways to determine CPU speed in Windows XP or in Windows Server 2003

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SYMPTOMS

This article describes the different locations where CPU speed is reported in Microsoft Windows XP and in Microsoft Windows Server 2003.

Note CPU speed may be reported differently in some locations. For example, the System Properties dialog box displays basic information about your computer, including the computer's processor speed. However, the value for the processor speed in this dialog box may differ slightly from the manufacturer's specification.

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MORE INFORMATION

In Windows XP and in Windows Server 2003, CPU speed is reported in the following locations:

The System Properties tab
To view the CPU speed on the System Properties tab, right-click My Computer, and then click Properties. Click the General tab. CPU information is listed in the first or second line of the Computer area.

The CPU information that is listed in the Computer area is retrieved from the ProcessorNameString entry under the following registry subkey:
HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System\CentralProcessor\0
Note In this example, 0 refers to the first CPU in the computer. In a multiprocessor system, 1 refers to the second physical CPU, or the second logical CPU in a system, such as a Intel hyper-threading technology system, that use multiple logical cores.

Windows reads the CPUID at startup and populates the ProcessorNameString entry accordingly. The CPUID string is the CPU brand string that is returned from the CPUID instruction. Some processors may include the CPU’s maximum-rated frequency as part of the CPU brand string.

The second or third line of the Computer area is calculated by the kernel very early during the initialization of Windows. Computers that use processor power management features, such as Advanced Configuration and Power Interface (ACPI) processor performance state technologies, may start with the processor running in a decreased performance state. This behavior reduces power consumption and avoids thermal problems until an ACPI-aware operating system can take control of these features. This initial speed setting is determined by the system designer and is controlled by the BIOS. When the system starts at a decreased performance state, the kernel performs the early CPU speed calculation before ACPI and the Windows processor driver have loaded. Therefore, the kernel incorrectly uses the reduced frequency rate to determine the maximum frequency of the processor.

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System Information utility
To use the System Information utility to see CPU speed, click Start, click Run, type Msinfo32, and then click OK. Click System Summary. CPU speed is displayed in the Processor line.

This information is updated dynamically whenever you run the System Information utility. The utility uses the Windows Management Instrumentation (WMI) component of the Windows operating system to retrieve the current processor performance state from the processor driver.
Help and Support Center
To use the Help and Support Center to see CPU speed, use one of the following methods.
- Method 1: View Detailed System Information
  1. Click Start, and then click Help and Support.
  2. Click What's new in Windows XP, click Tools, click Advanced System Information, and then click View Detailed System Information.
- Method 2: My Computer Information
  1. Click Start, and then click Help and Support.
  2. Click Use Tools to view your computer information and diagnose problems.
  3. In the Tools list, click My Computer Information, and then click Find information about the hardware installed on this computer.
Note Both of these methods use the System Information utility to retrieve CPU information.
Device Manager
To use Device Manager to determine CPU speed, click Start, click Run, type Devmgmt.msc, and then click OK. Expand Processors to see CPU information.

This information is retrieved from the FriendlyName entry under a registry subkey that is similar to the following:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\ACPI\GenuineIntel_-_x86_Family_15_Model_<number>\_0
Note In this example, 0 refers to the first CPU in the computer. In a multiprocessor system, 1 refers to the second physical CPU or to the second logical CPU in a multiple logical core processor system.

The information in the FriendlyName registry entry is retrieved directly from the CPU by using the CPUID instruction from the processor driver. The information is retrieved when the driver is initialized or when the computer is restarted. If this information changes at some point, either because of corruption or because of user modifications, this information is updated with information that is returned directly from the processor or processors. The CPU speed is referred to as the "Brand String" or the "Friendly Name".

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DirectX Diagnostic Tool
To view the CPU speed in the DirectX DiagnosticTool, click Start, click Run, type DXDiag, and then click OK. Click the System tab. CPU information is displayed in the Processor line. The DirectX Diagnostic Tool uses the CPUID to retrieve CPU speed information.
Windows Management Instrumentation Tester utility
You can use the Windows Management Instrumentation Tester utility to determine the current speed (CurrentClockSpeed) and the maximum speed (MaxClockSpeed) of the CPU. WMI uses the WBEMTEST and WMIC tests to retrieve this information.

To use the WBEMTEST test to determine the current speed and the maximum speed, follow these steps:
1. Click Start, click Run, type wbemtest, and then click OK.
2. Click Connect.
3. In the namespace box at the top of the dialog box, type root\cimv2, and then click Connect.
4. Click Enum Classes.
5. Click Recursive, and then click OK. Do not enter a superclass name.
6. Locate and then double-click Win32_Processor (CIM_Processor).
7. Click Instances. The CPU instances on the computer are displayed. Double-click the CPU that you want. For example, double-click Win32_Processor.DeviceID="CPUO".
8. In the Properties box, scroll down to see MaxClockSpeed and CurrentClockSpeed.
System Monitor
If your computer supports ACPI processor performance states, such as Enhanced Intel SpeedStep technology or AMD PowerNow! technology, you can use the System Monitor part of the Windows Performance tool to determine current CPU speed.

To use System Monitor to determine CPU speed, follow these steps:
1. Click Start, click Run, type perfmon, and then click OK.
2. Remove the default counters.
3. Right-click the chart, and then click Add Counters.
4. Click ProcessorPerformance in the Performance object box.
  
  Note If ProcessorPerformance is not listed in the Performance object box, follow these steps:
  1. In the Performance object box, click WMI Objects, click HiPerf Classes in the list of counters, and then click Add.
  2. Click Close, and then remove the HiPerfClasses counter.
  3. Right-click the chart, and then click Add Counters.
  4. Click ProcessorPerformance in the Performance object box.
5. Click % of Maximum Frequency in the list of counters, and then click Add. Alternatively, you can click Processor Frequency in the list of counters, and then click Add.
  
  Note If you use the Processor Frequency counter, you must also set the y-axis maximum scale to handle your processor’s maximum frequency. Otherwise, the counter will appear to run at the top of the scale.
Windows uses processor performance states to comply with the power scheme and the processor dynamic throttling policy. To test demand-based switching, verify that your power scheme is set to Portable/Laptop in Power Options in Control Panel. This power scheme uses the Adaptive processor dynamic throttling policy. Alternatively, you can use the Powercfg.exe utility to set your processor policy to Adaptive.

For additional information about the Powercfg.exe utility, click the following article number to view the article in the Microsoft Knowledge Base:
324347 (http://support.microsoft.com/kb/324347/ ) How to use Powercfg.exe in Windows Server 2003

If you use an Adaptive processor policy, the current processor speed will change in response to an increased workload. On some portable computers, the system may limit the highest performance state currently available when on battery power. In this case, you will see the top frequency that is reported fall to a value that is lower than the frequency that the CPU runs at while on AC power.
Additional locations
There may be other locations where CPU speed information is displayed, depending on your computer hardware. For example, some computers display CPU speed when the computer first starts. The system BIOS may also show CPU speed. The information in these locations is not controlled by the operating system but may be useful to help determine CPU speed.

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The CPU returns all its information in registers. For more information about the CPUID, see pages 3 through 115 of the Intel IA-32 Architecture Guide VOL 2. (See "Table 3-6: Information Returned by CPUID Instruction".)

For information about how to contact the third-party companies mentioned in this article, visit the following Microsoft Web site:

http://support.microsoft.com/gp/vendors (http://support.microsoft.com/gp/vendors)

For additional information about how the processor speed is reported to a computer, click the following article numbers to view the articles in the Microsoft Knowledge Base:

312104 (http://support.microsoft.com/kb/312104/ ) How processor speed is reported to a computer

311051 (http://support.microsoft.com/kb/311051/ ) CPU speed in System Properties dialog box may differ from actual CPU speed

For information about the Microsoft support policy for multiprocessor systems and processor steppings, visit the following Microsoft Web page:

http://www.microsoft.com/whdc/system/sysinternals/SMP.mspx (http://www.microsoft.com/whdc/system/sysinternals/SMP.mspx)

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.

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