Servicing Stack Updates (SSU)

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Servicing Stack Updates (SSU) seem to cause a lot of confusion.  Users see posts mentioning a SSU update but when viewing Update History, only the latest Cumulative Update is listed.  So, what is the Servicing Stack and why are the updates important?

What is the Servicing Stack?

Simply stated, the Servicing Stack is what actually installs Windows Updates.  However, it also contains the "component-based servicing stack" (CBS).  The CBS is key to DISM, SFC, as well as changing Windows features or roles, and repairing components.

Why are the SSU Updates Important?

The Microsoft Docs article referenced below explains the importance of SSU's as follows:

"Servicing stack updates improve the reliability of the update process to mitigate potential issues while installing the latest quality updates and feature updates. If you don't install the latest servicing stack update, there's a risk that your device can't be updated with the latest Microsoft security fixes."

As an example of a SSU update, following are the issues addressed in the July 26, 2019 Servicing Stack Update for Windows 10, 1903 x64-based Systems:

• Addresses an issue in which an update may not install with certain other updates and upon start up after installation of the other updates, will require a second scan of Windows Update and a second restart to complete installation.
  
• Addresses an issue in which reserved disk space may not be returned to free space when installation of Language Packs or Features on Demand (FODs) fails or is canceled.  The disk space is returned to free space when Storage Sense is run.
  
• Addresses an issue when Windows Update Check for updates is run during the installation or uninstallation of an update, Features on Demand (FODs) or Language packs, which may cause the installation to fail and may cause a restart to take up to an hour.
  

Getting the SSU:

When there is a Servicing Stack Update released with security or cumulative updates, the updates are automatically installed with Windows Update (you won't see the SSU offered in the list of updates available).  Because each Servicing Stack Update replaces the complete "stack" they do not require a restart.

If you are unsure whether you have the latest Servicing Stack Updates installed, the list of SSU's is at https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/ADV990001.  Locate the update for your operating system.  Clicking the KB number will take you to the update, which includes the date of the last update.  You can now find the date of the last update on your device in the link to "View installed updates" located in Programs and Features of the Control Panel.

References:

• ADV990001 | Latest Servicing Stack Updates
  
• Servicing stack updates (Windows 10) | Microsoft Docs
  
• Windows Update History:
  
  
  
  • Windows 10
    
  • Windows 8.1
    
  • Windows 7