With Windows 10, quality updates are cumulative. Installing the most recent update ensures that you receive any previous updates you may have missed. We used a cumulative update model to reduce ecosystem fragmentation, and to make it easier for IT admins and end users to stay up to date and secure. However, cumulative updates can prove challenging when it comes to the size of the update and the impact that size can have on your organization’s valuable network bandwidth.
When a new Windows 10 feature update is released, the first cumulative update is generally between 100-200 MB in size. Across all versions of Windows 10, cumulative updates grow as additional components and features get serviced, pushing the size to somewhere between 1-1.2 GB. Generally, this happens within the first 6-8 months after the release of a feature update.
To help you reduce the burden on your network bandwidth, yet still receive the same equivalent update, Microsoft designed three different update types:
- Full updates have all the necessary components and files that have changed since the last feature update. We refer to this as the latest cumulative update, or LCU. It can quickly grow to a little over 1 GB in size, but typically stays that size for the lifetime of that supported version of Windows 10.
- Express updates generate differential downloads for every component in the full update based on several historical bases. For example, the latest May LCU contains tcpip.sys. We will generate a differential for all tcpip.sys file changes from April to May, March to May, and from the original feature release to May. A device leveraging express updates will use network protocol to determine optimal differentials, then download only what is needed, which is typically around 150-200 MB in size each month. Ultimately, the more up to date a device is, the smaller the size of the differential download. Devices connected directly to Windows Server Update Services (WSUS), System Center Configuration Manager, or a third-party update manager that supports express updates will receive these smaller payloads.
- Delta updates include only the components that changed in the most recent quality update. Delta updates will only install if a device already has the previous month’s update installed. For example, assume in May that we changed tcpip.sys and ntfs.sys, but did not change notepad.exe. A device that downloads the delta update will get the latest version of tcpip.sys and ntfs.sys, but not notepad.exe. Delta updates include the full component (not just the individual files) that changed. As a result, they are larger than express updates, often around 300-500 MB in size.
Regardless of which type of update is installed on a device, that update is fully cumulative and installing the latest update will ensure that the device has all the necessary quality and security improvements.
This raises an important question: why make delta updates available if express updates are more optimized and don’t require the previous month’s update already be installed? Delta updates were originally created because the express update protocol was only available to devices connecting directly to Windows Update or Windows Server Update Services. In January 2017, the express protocol was extended to all 3rd party update management systems; however, we continued to ship delta updates to give companies and third-party update management tools time to implement support for express updates.
Currently delta updates are available for the following versions of Windows 10:
- Windows 10, version 1607
- Windows 10, version 1703
- Windows 10, version 1709
- Windows 10, version 1803
Now that express update support for third-party update managers has been available for over a year, we plan to stop shipping delta updates. Beginning February 12, 2019 Microsoft will end its practice of creating delta updates for all versions of Windows 10. Express updates are much smaller in size, and simplifying the cumulative options available will reduce complexity for IT administrators.
For more information on optimizing update bandwidth and more details about express updates, see Optimize Windows 10 update delivery. To learn more about Windows as a service, check out the new Windows as a service page on the Windows IT Pro Center.