How To Add Cores To A VMWare Guest

Why would you want to do this? I’ll tell you why. Some software is licensed by the socket meaning you can load up the number of cores you use and still pay for only the sockets used. For example, a single quad-core CPU would cost the same as a single core processor and still cost the same. Windows Standard and SQL Server Standard editions are typical examples of software that works this way.

This leads us to a new problem. When you add CPUs to a VMWare guest it adds the new CPUs as sockets rather than cores. Which in turn means that if you assign 8 CPUs to a Windows Standard server you will only see 4 CPUs!

imageThe way around this is to tell VMWare to present the vCPUs as cores rather than sockets. To do this we change the number of CPUs to the total desired amount. This number must be a multiple of 2 (eg. 2,4,8,16). In this example we’ll use 8 as the total number of cores we want presented to the operating system.

The second number we need to know is how many cores we want to present per socket. This number must divide evenly into the total number of vCPUs listed above. In our example we’ll choose 4 – Ie. 4 cores by 2 sockets –> 8 cores. VMware will automatically determine the number of sockets required by dividing the total number of CPUs (cores) requested by the number of cores per socket specified.

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This number is assigned to the Configuration Parameter cpuid.corespersocket. This option is found under the guest settings under Options –> Advanced –> General and then click on Configuration Parameters. Add a new row to the bottom called cpuid.corespersocket and set the value as desired (4 in this case).

Save your settings are restart the virtual machine. Opening task manager should now show 8 cores coming from 2 sockets.

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