I was working on a users desktop the other day who had an SSD installed a while back (back when 128GB were silly prices!) and it could only hold 64GB and it was full (well around 500kb free). This meant her .ost for Outlook couldn’t expand, causing no end of problems for her. Cleaning out temp files and rebuilding the .ost managed to bring back around 2GB which just wasn’t enough really so after hunting around on the drive to find where the rest of the space had gone I found the WinSXS folder. Now this folder was changed from XP to Vista quite a bit from the old .INF files being in there in XP to .mui, .exe’s in Vista and beyond. This folder allows you to run application such as SFC (System File Checker) or when installing additional features and roles in Server 2008 etc. As handy as this is, it can take up a great deal of space, especially when Service Packs are installed (which was the case for this poor user). To help clean this folder up there is a handy tool built into Windows, which can be run from the command prompt (you need to run the command prompt in Elevated Mode to run. To do this, hold down shift and right click on the command prompt icon and select Run as administrator…) which does a nice job of doing it all for you. Please bear in mind after this runs, you won’t be able to roll-back from the Service Packs. The command to run is below:

DISM /online /Cleanup-Image /SpSuperseded

This will take around 20-30minutes to run (depending on the OS and how much space it can reclaim) and can usually bring back around 3-5GB, which is the perfect amount of time to crack open a can of beer 

WinSXS size before command was run

WinSXS size after command was run