https://www.microsoft.com/licensing/existing-customers/product-activation.aspx
If your organization has fewer than 50 PCs, the best option is to use Multiple Activation Keys (MAK) with Volume Activation Management Tool (VAMT).
VLKs can be used only with Volume Licensing products; they cannot be used with retail software or software that is preinstalled on a new computer (original equipment manufacturer, or OEM, products).
http://technet.microsoft.com/en-us/library/dd979803.aspx
Activation Improvements in Windows 7
Modified Hardware Tolerance Values
With Windows 7, customers are less likely to trigger an out-of-tolerance condition that results in a need to reactivate the computer.
Original Equipment Manufacturers
Original Equipment Manufacturer (OEM) activation is a perpetual, one-time activation that associates Windows 7 with the firmware (BIOS) of a computer. This occurs before the computer ships to the customer, so the end user or organization is not required to take any additional actions. The copy of Windows 7 that the OEM installs on a computer is valid only on that particular computer, and it can be reinstalled and reactivated only from the OEM-provided recovery media.
Windows 7 Activation and Licensing
Customers can obtain licenses for Windows 7 through one of three channels: retail, original equipment manufacturer (OEM), or Volume Licensing (VL). One software license is always required for each computer that uses Windows
http://www.neowin.net/news/report-microsoft-to-change-windows-8-oem-activation
http://gizmodo.com/5931972/microsoft-changes-up-its-windows-8-activation-policy-to-curb-the-rampant-piracy-it-seems-to-expect
This time, Microsoft is demanding a little more, and will be requiring OEMs to write a unique activation key into the BIOS of each machine, and ship them with the operating pre-installed. OEMs also going to have to get all keys directly from Microsoft, no ifs ands or buts
http://www.neowin.net/news/windows-8-activations-made-possible-by-belarus-customs
Windows 8 activations made possible by Belarus Customs
Thanks to a tip sent into Neowin, we now know why it was possible to activate the Windows 8 RTM leaks illegally for a short time, and well before it should be legally possible.
The bypass, which is now shut down, was made possible by Belarusian customs officers who setup their own Key Management Server (KMS). It was one of the first servers that pirates had been using to activate the Windows 8 RTM leaks, and not just anywhere, but in a state institution - Gomel customs.
It's unclear if they were contacted by Microsoft, or simply shut it down due to over-capacity.