WinSxS
Updated: 10/17/2017 by Computer Hope
Short for Windows Side By Side, WinSxS is a folder in Windows XP, Vista, 7, and 8 that stores different copies of DLL and system files. Because programs can use the same DLL (dynamic-link library) file, this folder stores the different files for compatibility reasons and when older versions need to be restored.
The WinSxS folder is located at C:\Windows\WinSxS and it is not abnormal for the size of the folder to be several gigabytes. The size of the WinSxS folder varies between Windows versions because Vista and 7 do not have the i386 folder, which is where Windows XP stores cached DLL files.
Warning
The WinSxS folder and its contents should never be deleted manually. To clean files from the computer, we suggest using Disk Cleanup tool.