CLG - Windows Catalog File is a file extension that is mainly used by different Windows System Image Manager. It also consists of various types of information which can describe the contents of a .WIM image and much more. This really comes in handy when you need it the most. You can go online to get this file extension when you are ready for a complete installation process. There also happens to be CLG files that can be a lot less in megabyte sizes than WIM files which tend to be a lot larger. You should also take that into consideration when you begin to download these files to your computer.