Hello I have a questions about processors on a Windows Server 2008 server.I have a Windows Server 2008 x64 server. It is the management server in a EBS enviornment, so it's a domain controller. It currently has two processors and I would like to add 2 or 6 more.My questions is: How tolerant is Windows Server 2008 x64 to changing processor count? It was installed with 2 processors, so I am thinking that it should already have a Multi processor HAL. However, I have read that changing the number of processors can lead to instability, but it's really dependant on the O.S.Should I expect to run into instability problems, might have to rebuild HAL or do a repair install of windows?Also, this server is a Virtual Machine in a VMWare enviornment. I am addressing the issue via a VMWare perspective also. However, I am posting this discussion in hopes of addressing the issue from a Operating System perspective. Becuase it's VMWare, the O.S. is only going to see the processors as cores, not sockets.So, I would be shutting down the Server, going from 2 to 4 or 6 processors, and powering it back up.

Windows 2008 should automatically detect the 2nd processor and update itself from. When it boots up check in device manager to see if the CPU is recognised and drivers are installer, or check in task manager to check if the cores/ cpu's can be seen. You might need to reactivate since its a change to the hardware.

Hi There,You are referring to the Hot Add CPU feature which got introduced in windows 64bit Datacenter / windows 2008 64bit enterprise edition. Requirements=========--supports itanium based OS --Your hardware should support hot add feature As you mentioned your OS is running on VM , there is an option in VMware for Hotadd CPU functionality, and IMHO when Your OS needs to communicate to the hardware, its the ESX server which would respond and not the OS , OS acts as an abstract and not the base which means Any communication from kernel to HAL are viceversa are dealt in OS , but from HAL , the instructions are passed down to the devices, either CPU / memory, HAL provides the support for multiple devices to be compatible with OS . In your scenario , i would recommend you to post your query in VMware forum because HAL depends on underlying hardware whcih might be ESX in your environment.You can check if your server is runnring with ACPI Multiprocessor HAL / ACPI uniprocessor HAL using device manager --> system devices

If possible i'd like to contuinue this thread as i have similiar questions and have been unable to find any definitive info on Win2008 X64 processors. Under Device manager --> system devices on my Win2008 x64 servers it simply says ACPI x64-based PC. There is no designation of it being a multi or uni processor. I have looked at both my VMs and my physical W2K8x64 servers and they all say the same. I had once read (can't remember where..) that w2k8x64 has done away with the Mutli/Uni HAL concept and now there is only one regardless of the processor count. Can anyone confirm or deny this? In VMWare, it is recommended that we change the virtual server's HAL to match the virtual processor count (uni or multi) but this option does not appear to exist in w2k8x64. comments anyone?