Windows Activation Methods Explained: KMS, MAK, OEM and Digital License

Windows activation is the process Microsoft uses to verify that a copy of Windows is genuine and properly licensed. But not all activation works the same way. Depending on how the license was purchased, Windows uses one of four different activation mechanisms: KMS, MAK, OEM SLP, or digital license. This guide explains each method, how it works technically, and when it applies.

KMS Activation (Key Management Service)

KMS is Microsoft's volume activation method for organizations. Instead of each computer contacting Microsoft directly, clients activate against a KMS host server on the local network. The client uses a Generic Volume License Key (GVLK) - a public key published by Microsoft for each Windows edition - and discovers the KMS host through DNS or manual configuration with slmgr /skms.

KMS activation lasts 180 days and automatically renews every 7 days while the client can reach the host. Communication happens over TCP port 1688. A KMS host requires a minimum activation count before it begins activating clients: 25 for Windows client editions, 5 for Windows Server.

For a complete walkthrough of volume activation concepts, see the complete Windows licensing guide which covers OEM, Retail, and Volume licensing models in detail.

MAK Activation (Multiple Activation Key)

A Multiple Activation Key activates a fixed number of computers directly against Microsoft's activation servers. Unlike KMS, there is no local host and no renewal cycle - each activation is one-time and permanent, but it decrements the remaining activation count on the key. MAK is suited for smaller organizations or isolated machines that cannot maintain contact with a KMS host.

OEM SLP Activation

OEM System-Locked Pre-installation is the method used by manufacturers like Dell, HP, and Lenovo. The product key is embedded in the BIOS or UEFI firmware, and Windows activates automatically during first boot by matching the firmware SLIC table against an installed OEM certificate. OEM licenses are permanently tied to the original hardware and cannot be transferred.

Digital License

Introduced with Windows 10, a digital license (formerly digital entitlement) links activation to a hardware hash stored on Microsoft's servers. After the first online activation, reinstalling the same edition on the same hardware activates automatically without entering a key. Linking the license to a Microsoft account also enables the Activation Troubleshooter after hardware changes.

Which Method Applies to You

• Home user with a pre-built PC: OEM (embedded in firmware)
• Home user with a custom-built PC: Retail key or digital license
• Organization with 25+ PCs: KMS with GVLK keys
• Organization with few or offline PCs: MAK

If you need the actual product keys for volume activation, Microsoft publishes them publicly. The full GVLK key list for Windows and Office includes every edition from Windows 7 through Windows 11 and Server 2025.