VCPU issue and Windows servers

[marius1]

Using Converter I can easily change the number of VCPU, virtual CPUs.

If I change the number of CPU for a Windows Server shoud I reinstall or reconfigure the guest Windows Operating System (let's say Windows Server 2003 or Windows Server 2008) to make it aware of the new number of CPUs?

In other words,

• if I convert a single processor Windows server to a 2 processors Windows server have I to do anything to make it work fime as a SMP virtual machine?
  
• if I convert a SMP viertual machine to a single processor virtual machine have I to do anything from the Windows side to make it work fine?
  

Regards

marius

[a_p_]

I'd suggest you make sure you are always running the OS with the correct HAL. Usually the newer OS's automatically pick up the multi-processor HAL when you add a CPU, however they don't revert to a uni-processor HAL automatically when you remove a CPU.

see e.g. http://kb.vmware.com/kb/1003978

André

[marius1]

After some investigation from the Microsoft point of view it looks (I'ts my personal opinion, I can be wrong!!!) that Windows Server 2008 allows increasing or decreasing the number of VCPUs without the need of any configuratiion change, while older versions require some additional chach: is it true?

Regards

marius 

[AndreTheGiant]

From Vista the HAL is generic and you can change the number of vCPU without change anything in the OS configuration.

The problem was in previous version, expecially to go from a multi-CPU HAL to a uni-CPU HAL.

Andre