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What are the differences (and maybe pros and cons) of KMS and MAK license activation for Windows 7?

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Assuming that you are in an Active Directory domain environment with at least 25 computers on-site (or on your reliable, mission-critical WAN or VPN) running any combination of Server 2008, Server 2008 R2, Windows Vista, and Windows 7, you will want to use KMS.

Table of Pros and Cons, MAK vs. KMS

Detailed pros/cons:

MAK:

  • Pro: When you activate a product with a MAK key, it is activated permanently. It does not need to reactivate on any pre-set interval.

  • Con: You must enter a product key each time you set up a new workstation or server. Operating systems will not activate automatically.

  • Con: Each MAK key has a limited number of activations. (You still may be able to activate more computers than licensed. You are responsible for maintaining records of your licensing compliance.)

  • Con: Hardware changes may invalidate your activation. If your MAK key's activation count is depleted, reactivating will require a phone call to Microsoft.

KMS:

  • Pro: Your KMS server can activate unlimited computers without further approval from Microsoft. When you activate a Windows product with a KMS key, that computer becomes your KMS server. Normally, the KMS server that activates your Win7 workstations will be running Windows Server 2008 R2, activated with a Server 2008 R2 KMS key. This is because a Server 2008 R2 KMS can activate any Windows 6.x product, including Vista, Win7, and Server 2008. Although the KMS key itself will activate only a few times, this is not a limitation because you need only one KMS server. (You are still responsible for maintaining records of your licensing compliance; unlimited activations does not mean unlimited licenses.)

  • Pro: You do not need to enter a product key each time you add a new workstation or server. They will activate against your KMS server automatically upon joining your domain. (This works with Vista, Server 2008, Win7, and Server 2008 R2. The KMS must have a proper SRV record in your enterprise's DNS.)

  • Pro: Hardware changes that invalidate a computer's activation will resolve automatically after a reboot, with no phone call to Microsoft, because the computer will reactivate with the KMS server automatically.

  • Con: The KMS server must receive activation requests from at least 25 products (any combination of Win7/Vista, Server 2008, and Server 2008 R2) before it will grant activation for Windows 7. Therefore, if you do not have at least 25 computers and/or VMs running Windows 6.x operating systems, you cannot use KMS in your enterprise.

  • Con: KMS activations expire after 180 days. All KMS clients must have network access to the KMS server at least once every 180 days in order to reactivate.

Transitioning from MAK to KMS:

  • When you are transitioning to KMS, you may need to convert existing computers from MAK activation to KMS activation in order to reach the minimum count of 25. It is possible to convert computers from MAK to KMS activation remotely using slmgr.vbs.

  • Microsoft publishes lists of product keys that will configure Windows Vista/7/Server2008/R2 as KMS clients instead of using MAK activation.

  • The following commands can be executed by the domain administrator at a Windows command prompt to change a Windows 7 Professional computer named EXAMPLE-PC from MAK activation to KMS activation, activating against KMS-HOSTNAME. (Note: The product key included after the /ipk switch is a special key that tells Windows 7 to contact a KMS server. For other versions of Windows, please refer to the TechNet articles linked above for the correct keys):

    slmgr.vbs EXAMPLE-PC /ipk FJ82H-XT6CR-J8D7P-XQJJ2-GPDD4

    slmgr.vbs EXAMPLE-PC /skms KMS-HOSTNAME

    slmgr.vbs EXAMPLE-PC /ato

  • Such changes are to be made at your own risk, and only after careful planning. Changing a computer's product key will invalidate a computer's existing MAK activation. If you are not able to get the KMS working correctly, e.g. because you do not have the minimum 25 computers or the KMS is not configured correctly, this could create major problems. As always, RTFM (and test) before you leap!

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Computers activated with a KMS must check-in with the KMS once ever 180 days. If the computer isn't going to be able to communicate with the KMS (if it's, say, an off-site employee w/ no access to the LAN) then a KMS activation probably isn't the way to go.

After a MAK activation, no further communication with Microsoft is required. This makes it work well for computers that can't communicate to your KMS. A MAK key can be used a limited number of times, so if you have a number of computers (I believe Microsoft recommends KMS for 50 or more computers).

Microsoft has some official recommendations re: product activation, as well.

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There's also a 25 computers minimum for each workstation OS, and a minimum of 5 for each server OS. –  Chris S Jul 20 '10 at 17:56
    
@Chris: The limit is not for each OS. It is a count of total products. For example, if you have 5 computers running Server 2008 R2, 5 computers running Server 2008 (not R2), 5 computers running Vista, and 10 computers running Windows 7, for a total of 25, and all of them are pointed at the same Server 2008 R2 KMS, then all of them will activate successfully against the KMS. I have done this in a real-world production environment. –  Skyhawk Jul 20 '10 at 18:04
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