In Windows 7 and Windows 8, there is a new folder C:Windowswinsxs, that stores basic .dll files and other data files. All earlier versions of the .dll and data files are also stored. This is a process that can greatly increase the space that occupies the disk. Besides this, a lot of space is occupied by the backup folder, which is really very large after installing a Service Pack, such as SP 1 for Windows 7. The purpose of this process is to provide the option of rolling back to previous versions of files.
To delete the disk space, just run a single command. Open a command prompt window (Start and in the search box click cmd.exe) and type the following:
dism /online /cleanup-image /spsuperseded /hidesp
This process lasts about 5 minutes and frees up to 3GB of disk. After this you cannot roll back to previous versions of files