If you're a Windows administrator, you would certainly know already that even business customers have to activate Windows Vista. There are several ways to do it, and KMS will probably be the one that most companies will use. Microsoft's own documentation is a bit long winded because it also covers uncommon cases. In this post, I summarized the most important facts about KMS. It will help you get an overview of the activation procedure via KMS.

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Retail versions of Vista have to contact Microsoft for activation. This isn't feasible for business customers because they would have to enter a separate product key on every machine. Another option for business customers is to work with so called MAK keys. I will write about this in another post.

The biggest advantage of KMS is that you don't have to mess with product keys and manual activation on your Vista machines. You only have to activate the KMS once, and then your Vista computers are activated by connecting to the KMS.

Here the essentials about KMS:

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KMS facts and requirements

  • One KMS host can service thousands of Vista clients.
  • You can run a second KMS host as backup system.
  • KMS is available for Windows Server 2003 SP1.
  • You can also use a Vista machine as KMS host.
  • Also check out my post about the differences between running the KMS host on Vista and on Windows Server 2003 .
  • KMS activation can be used for Vista Business and Enterprise edition.
  • Activation for the OEM edition is only supported if the KMS host is a Vista machine.
  • At least 25 Vista machines have to connect to the KMS before clients can be activated; the number of machines connected to the KMS is referred to as n-count or n value.
  • Virtual machines can be activated by the KMS, but they don't contribute to n-count.
  • The KMS host mustn't run in a virtual machine.

KMS time periods

  • New installed Vista machine have a 30-day grace period to activate.
  • If a Vista computer didn't activate during this time, it will go into Reduced Functionality Mode (RFM).
  • KMS clients which are not yet activated contact the KMS host every two hours (value configurable).
  • Afterwards they auto-renew their activations every 7 days (value configurable)
  • KMS clients have to renew their activation at least after 180 days.
  • If activation fails, the client has again a 30 days grace period before going into RFM.
  • The KMS host contacts Microsoft every 180 days. If there was a misuse with your KMS key, your KMS host will be disabled! (I didn't find this information in the documentation, but a Microsoft official said this on an info session at our computer center.)

Originally, I also planned to write about the KMS installation in this post, but then I ran into some interesting problems. I wasn't able to active KMS on a Windows server. However, the same key worked on a Vista machine. I also didn't find srv records of the KMS host in our Windows DNS server. Did anyone get this working? To be continued…

  1. Max 17 years ago


    Yepp, I did not get it to work on a Windows 2003 Server either. I even tried it on Windows Longhorn Server. No way. Concerning the SRV records I would place them manually like you can read here: http://its.psu.edu/mskms/howtoconnect.html


  2. Max, thanks for the link. I am going to try it soon.

  3. Jouni 17 years ago

    I have had interesting experiences concerning KMS-key. I have succesfully activated 5 workstations using KMS key. There was no KMS-server around when doing that. Those workstations were in workgroup neigbourhood. When i joined one of those systems in domain Vista deactivated itselfs. When i tried to activate workstation in domain neighbourhood, there was an error message stating that KMS-server was not found. I then joined workstation back to workgroup and tried to activate again. This time i was presented an error message saying that my key was allready in use….sigh

  4. Jouni, good to know that we are not the only ones who mistakenly used a KMS key to activate Vista clients. 😉 I posted an article about this story.

  5. Silas 15 years ago


    Could you clarify your statement that the KMS host must not run on a virtual machine?

    The following extract from the “Volume Activation 2 0 Changes for Windows Server 2008 and Windows Vista SP1.doc” states that:

    KMS can be hosted on a virtual machine running Windows Vista RTM, Windows Vista SP1, Windows Server 2008 RTM, or Windows Server 2003 running KMS for Windows Server 2003 v1.1.

    My concern is that if vmotion moves the KMS host, it will break the activation of the KMS host because new hardware will be detected.


  6. Chad 13 years ago

    How about an update now that 2008 R2 and Windows 7 is out?

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