WINSXS directory in Windows Vista: What is it and why is it so large?

Of the many blogs that I read daily, the Core Team Blog  really interests me.

The below article on WinSxS is explains a lot about vista changes.

You may read full the article  @ http://blogs.technet.com/askcore/archive/2008/09/17/what-is-the-winsxs-directory-in-windows-2008-and-windows-vista-and-why-is-it-so-large.aspx

Effort is to capture some core points :

• Vista is no more an INF described OS. It uses componentization.
• A component in Windows is one or more binaries, a catalog file, and an XML file that describes everything about how the files should be installed.
• All of the components in the operating system are found in the WinSxS folder. The WinSxS is called Component Store quite often.
• The WinSxS folder is the only location that the component is found on the system, all other instances of the files that you see on the system are “projected” by hard linking from the component store.
• there is only one instance (or full data copy) of each version of each file in the OS, and that instance is located in the WinSxS folder.  
•  Looked at from that perspective, the WinSxS folder is really the entirety of the whole OS.

The bulleted points above explains why the folder is big initially. Further to this, the article explains the reason, why the folder grows with time.

•  In previous versions of Windows the atomic unit of servicing was the file, in Windows Vista it’s the component. 
• When Microsoft updates a particular binary, theyrelease a new version of the whole component, and that new version is stored alongside the original one in the component store.
• The higher version of the component is projected onto the system, but the older version in the store isn’t touched. 
• This is the reason for the component store to grow so large.
• Not every component in the component store is applicable, meaning that not every component should be projected onto the system.  For example, on systems where IIS is available but has not been installed, the IIS components are present in the store, but not projected into any location on the system where they might be used.
• So a single Post SP1 GDR package that contains an update to one component will end up installing four versions of that component in the WinSxS folder

Why the older components are not removed from the component Store ?

• The reason for this is to make the system more reliable.
• The component store, along with other information on the system, allows us to determine at any given time what the best version of a component to project is.
• That means that if you uninstall a security update we can install the next highest version on the system – we no longer have an “out of order uninstall” problem.

Still I am short of space.. Can I reduce the size of this folder ?

• The only way to safely reduce the size of the WinSxS folder is to reduce the set of possible actions that the system can take – the easiest way to do that is to remove the packages that installed the components in the first place.
•  This can be done by uninstalling superseded versions of packages that are on your system.
• Service Pack 1 contains a binary called VSP1CLN.EXE, a tool that will make the Service Pack package permanent (not removable) on your system,  and remove the RTM versions of all superseded components.

Reusing Joseph's - Author of this article - words to conclude this "So yes, the WinSXS folder is very large, and it will continue to grow as the OS ages. "


PS: The C:\Windows\winSxS folder on my Vista system is 5.6 GB :-)