Many people know that if you purchase a copy of Windows Server 2008 R2 Enterprise Edition then you get to run 4 copies of Enterprise or down level versions in a virtualised environment on that physical host for which the Enterprise license was purchased. This is true even if you don’t install Enterprise on the physical host. That is, you can install XenServer or VMWare and still take advantage of this fantastic deal.

What you may not be aware of though is that you can also but Windows Server 2008 R2 Datacenter Edition and run an unlimited number of Windows Server guest VM’s on that physical host. Datacenter is licensed per processor socket (not core) and you have to license a minimum of 2 sockets (processors) in the physical server but, and here’s the thing, with hexa (6) and octo (8) core processors now on the market then, with 2 octo-core processors and one physical core assigned to each VM then you can run 16 VM’s on a single host for the price of 2 Datacenter Edition licences or 4 Enterprise Edition licences. If you go for even higher densities then the gap widens still further. With the difference in price between versions being only a couple of hundred bucks then there are savings to be made in even the smaller virtualised data centers.

But, how do you tell which is the right choice for you ? Microsoft have published an online tool to help you out. Simply type in the price you pay for Enterprise, Standard and Datacenter Editions, the number of processors per server and the average number of VM’s per server and the calculator will tell you which is the cheaper option to go for.

You can find this tool online at http://www.microsoft.com/windowsserver2008/en/us/hyperv-calculators.aspx.