Product Key Types
Retail, OEM, MAK, KMS Host, and GVLK keys
Microsoft product keys fall into a small number of documented types, each tied to a particular distribution channel and activation method. All Microsoft product keys share a common 25-character grouped format (XXXXX-XXXXX-XXXXX-XXXXX-XXXXX), but the type is determined by metadata associated with the key in Microsoft's activation back end, not by its visible format.
Installing a key against a SKU it does not match results in 0xC004F050(product key is invalid); the Software Protection Platform validates key-to-SKU mapping before accepting any product key.
See also: GVLK Keys, HWID Digital License, Volume Licensing Programs.
History
The Retail and OEM categories date back to Windows 95. The Volume License Key (VLK) category was added in Windows 2000 and split into MAK, KMS Host key, and GVLK with Volume Activation 2.0 in Windows Vista. OEM keys evolved with each generation, culminating in OA 3.0 (System Locked Pre-installation) in 2012, which embeds the key in firmware where it is read directly by the Software Protection Platform.
Technical details
Keys are installed with slmgr.vbs /ipk <key> on Windows or cscript ospp.vbs /inpkey:<key> on Office. The first three groups of a key identify the product family to the activation back end; the remaining groups are checksum and entropy. The full key is not stored in the registry after activation — only the partial key (last five characters) is retained, visible in slmgr.vbs /dli output.
Key type table
| Type | Channel | Transferable | Activation |
|---|---|---|---|
| Retail (FPP) | Microsoft Store, retailers | Yes | Online digital licence; tied to a Microsoft account when linked |
| OEM (OA3) | Pre-installed by hardware manufacturer; embedded in firmware | No — bound to the original device | Read from ACPI MSDM table and digitally licensed |
| MAK | Volume Licensing | Per organization | One-time online or telephone activation, consuming a unit from a pool |
| KMS Host key (CSVLK) | Volume Licensing | Per organization | Installed on a KMS host; activated once against Microsoft |
| GVLK (KMS Client Setup Key) | Publicly published by Microsoft | N/A | KMS host or Active Directory-Based Activation |
Format and encoding
The 25-character key uses a 24-character alphabet (digits 2–9 and uppercase letters B, C, D, F, G, H, J, K, M, P, Q, R, T, V, W, X, Y, omitting visually ambiguous characters). OEM keys embedded in firmware are stored in the ACPI Microsoft Software Licensing (MSDM) table; they can be read with wmic path SoftwareLicensingService get OA3xOriginalProductKey on Windows 10 and 11.
Common issues
- Retail key on Volume Licensed media. Installs successfully but switches the SKU's licensing channel away from KMS / AD-BA; the device will require online activation.
- OEM key after motherboard replacement. The firmware key no longer matches the embedded entitlement; replacement parts from the OEM that include a new MSDM table restore activation.
- MAK installed on a system intended for KMS. Disables KMS / AD-BA on that host; remove the MAK with
slmgr.vbs /upkand re-install the appropriate GVLK. - KMS Host key installed on a client. Converts the client into a KMS host candidate but does not activate Windows; uninstall with
/upkand install the correct GVLK.
References
- Plan for volume activation — https://learn.microsoft.com/en-us/windows/deployment/volume-activation/plan-for-volume-activation-client
- KMS client setup keys — https://learn.microsoft.com/en-us/windows-server/get-started/kms-client-activation-keys
- Activate Windows — https://learn.microsoft.com/en-us/windows/client-management/manage-windows-10-in-your-organization-modern-management
- OEM activation overview (OA 3.0) — https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/oem-activation-3