WinSxS (introduced with NT6.0, Vista) is the component store. It stores most of system files which are versioned and it's what solved DLL hell. Files in other s

WinSxS (introduced with NT6.0, Vista) is the component store. It stores most of system files which are versioned and it's what solved DLL hell. Files in other system folders are hardlinks to them. On my 1 year old install, it's 9GB with only 4GB allocated i.e. with no hardlinks outside WinSxS. So delete stuff outside instead of messing up with this folder.