With Microsoft desktop operating systems (OS) are surprisingly simple when it comes to licensing. For each physical or virtual client that uses that operating system you can install one copy per license. This includes thin clients also. The only exception to this rule is if you have a volume licensing program – the desktop OS license is an upgrade. Typically, the licenses that come with your PCs when you purchase them are considered base licenses; therefore, you should only have to apply a volume licensed desktop OS license and you will be set.
Microsoft users with software assurance (SA) have the advantage of being allows to run up to four additional copies or instances of the OS without purchasing extra licenses. This will come in handy for virtualization.
For Desktop applications – a single license is required for each physical device running or accessing the software, therefore you may be required to purchase additional licenses if you have a virtual or thin client accessing that application.
This is one of the simpler licensing scenarios!