Since its inception, Microsoft has been interested in volume licensing, with the business sector being its main market. With the release of Windows XP in 2001, Microsoft introduced the activation of Microsoft Product , a DRM (Digital Rights Management) system to limit consumer software piracy by verifying the user`s product license application. However, at the time, volume-licensed versions of Windows XP were excluded from this measure. (See . Starting with Windows Vista, Microsoft has implemented two volume licensing methods for IT experts responsible for installing Windows in organizations that are both covered by Microsoft product activation: the first is the Multiple Activation Key (MAC) which is identical to Windows XP volume licensing keys, but which require product activation. The second key management server (SMS) and the corresponding keys. Hosts that are enabled via a KMS must connect to a software licensing server every 180 days.   Licenses using these schemes can be obtained through the Microsoft Software Assurance program. Transaction volume license agreement for business users with more than 250 users or devices.
Any customer computer with the appropriate kms customer installation keys can authenticate on any KMS server. The kms customer keys are well known to Microsoft and are publicly documented.  KMS servers need at least 25 customers to activate properly, but also to no longer count additional licenses beyond 50 and automatically accept each customer key as soon as the 25 customer threshold is reached. Microsoft Products and Services Agreement (MPSA) offers flexible call options on an ongoing, unsealed basis. This is a transaction licensing agreement for users who have more than 250 users or devices and who offer indeterminate user insurance and subscription licenses, with or without software, to public sector customers at the lowest available price level (volume D). Traditionally, a product key comes with computer programs. It acts as a password: the old computer programs ask the user to prove their right; In response, the user provides this key.