Gwxux.exe uses up a lot of CPU and makes things run slow. Windows 8.1 can also report that Gwxux.exe has stopped working. This is easy to fix, but first you have to know what gwxux.exe is.
Gwxux.exe is the process for upgrading to Windows 10 and runs in the background until you click on the white Windows icon in the notification area. After clicking on the notification, you can follow the wizard to reserve, then upgrade to Windows 10. After upgrading, the gwxux process will no longer be there to make your computer go slow. Alternatively, if you don’t want to upgrade to Windows 10, you can uninstall then hide the Windows 10 upgrade patch (listed as a kb article in Programs under the Control Panel, sorry you’ll have to Google what the kb number is).