Super-Networking Blog

If you are running Virtual Server 2005 on a server with multiple processors you should be aware that the virtual machines you run on the server can only use one processor. So if you have a four processor server and are running two Virtual Machines you will only be able to utilize two out of the four processors. To make things worse if you have hyper-threading enabled on your processors the Virtual Machines can only use one logical processor or half of the physical processor. This will slow down your Virtual Machines a lot.

It is always recommended that you disable hyper-threading to get the best performance out of your Virtual Machines. Dual core processors are fine because it is actually two full speed processors in one instead of cutting the processing power in half like hyper-threading does. That said Virtual Machines in Virtual Server 2005 can still only use one core on a dual core processor but it is the same as running one physical processor.

Also I am hearing that the new Microsoft Server 2008 Hyper-V server will be able to utilize multi-core processors in Virtual Machines. This will break the single processor restriction in the current 2005 server.