According to Microsoft, Windows 10 has “B,” “C,” and “D” updates—but never “A” updates! These updates are released at different times, contain different things, and are offered to different people. Let’s break all this down.
What Is a Cumulative Quality Update?
Microsoft calls these “quality updates,” and each is released once per month. This distinguishes them from the big “feature updates” like the October 2018 Update and 19H1 that are released once every six months, usually in the Spring and Fall.
Quality updates are cumulative, which means they contain all the fixes from previous updates. So, when you install the December cumulative update, you get the new security fixes from December as well as everything that was in the November and October updates, even if you haven’t installed those previous updates.
And, if you’re updating a new PC, you only have one big cumulative update package to install. You don’t have to install updates one by one and reboot in between each.
That’s all great, but the way Microsoft handles C and D updates is just bizarre. Microsoft tricks people it calls “seekers” into installing updates before they’re fully tested. But almost none of these people even realize they’re signing up to be “seekers.”
“B” Updates: Patch Tuesday
The big updates most people are familiar with come out on “Patch Tuesday,” the second Tuesday of the month. These are called “B” updates because they’re released in the second week of the month. That explains why there are no “A” updates, as Microsoft doesn’t generally release updates in the first week of the month.
B updates are the most important updates, featuring new security fixes. They also contain previously released security fixes from prior B updates and previously released bug fixes from prior C and D updates.