How to Resolve the Difference in the Number of CPU Cores Between Task Manager and Device Manager of a Windows 7 VM

Publication Date:  2015-03-04 Views:  491 Downloads:  5
Issue Description
A site uses a Windows 7 VM with 2 CPU cores. The site performs all required operations to adjust the number of CPU cores to 4. After the adjustment, however, the number of CPU cores displayed on Task Manager of the VM is still 2. The user checks device drivers and the CPU driver is normal. Then the user restarts the VM but the problem persists.
Handling Process
1. Click Start and then Run. In the Run dialog box, enter msconfig.

2. In the System Configuration dialog box, click the Boot tab and then Advanced options.

3. In the BOOT Advanced Options dialog box, deselect the check box in front of Number of processors.

4. Restart the VM.
The problem is resolved after the VM restarts.
Root Cause
1. The number of CPU cores displayed in Device Manager is 4, indicating that the system hardware has recognized 4 processors. Hence, this issue is not caused by the device layer or the virtualization layer. The number of CPU cores displayed on Task Manager is 2, indicating that the system software layer can recognize only 2 CPUs.

2. Check the registry of the VM. It is found that the number of CPU cores displayed in HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System\CentralProcessor is also 2, which is consistent with Task Manager.

3. Do as follows to check the system settings: Click Start and then Run. In the Run dialog box, enter msconfig. In the System Configuration dialog box, click the Boot tab and then Advanced options. In the BOOT Advanced Options dialog box, check the setting of Number of processors. It is set to 2 and the maximum value in the drop-down list is also 2, as shown in Figure 1.

Figure 1 Setting of Number of processors



Deselect the check box in front of Number of processors and restart the VM. After the VM restarts, check Task Manager. The number of CPU cores is correctly displayed as 4.
In the BOOT Advanced Options dialog box, select the check box in front of Number of processors, set it to 2, and restart the VM. Then this problem occurs again.
It can be concluded that the setting of Number of processors determines the number of physical cores that Windows uses to start up.

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