If you pay attention to the updates Microsoft rolls out each month or take note of what Windows Updates are on your Windows 8 PC or Windows Server 2012 Server, you may have seen some monthly rollup updates.
These update rollups are not cumulative updates. You do need to apply each of the monthly update rollups to get the fixes and enhancements from each month. Installing the February 2013 Update Rollup does not get you the January 2013 to October 2012 rollup updates. This is to say, these rollups are independent of each other. Searching on the KB number will discuss what each rollup is addressing that month. Note that these updates do not focus on a particular component as we have seen with previous cumulative or rollup type updates but are broader to Windows.
Continue at source:Update Rollups For Windows Server 2012 and Windows 8 Explained - Ask Premier Field Engineeri