The cumulative updates for Windows 10 are released every month with both security and non-security improvements in just one package. Microsoft uses three different types of updates, which are either full updates, express updates, or delta updates to make it easier for IT admins to stay up to date and secure.
Full updates have all the necessary components that may have changed since the last update. On the other hand, the express update would generate "differential downloads for every component in the full update based on several historical bases", but a user only has to download what files have been specifically changed. Delta updates are larger in size compared to express updates because they contain the full component, rather than just the changed files. They also require the previous month's updates to be installed.
Starting on February 2019, the company will retire the delta updates branch and focus on full updates and express updates. This is because it makes more sense to focus on express updates, which are more optimized, smaller downloads, and do not require the previous month's updates to already be 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," Microsoft explained how delta updates work. "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."
The delta updates are currently available for Windows 10 version 1607, version 1703, version 1709 and version 1803, but will be discontinued once these versions reach the end of their support.
"Beginning February 12, 2019 Microsoft will end its practice of creating delta updates for all versions of Windows 10," Microsoft's Mike Benson explains in a blog post. "Express updates are much smaller in size, and simplifying the cumulative options available will reduce complexity for IT administrators."