REG, Registry Data File (.reg)
The REG System file format
REG files are commonly found on Windows computers and other devices that run on the Windows operating system. What these files do is to update, repair or save data from the Windows Registry, a Windows database that stores information about the software installed on the device, when run. Custom REG files can help to change Windows in a way that fits their personal taste and requirements.
Technical details of REG files
Advanced users of Windows machines can actually create their own REG files. While the creation itself is not tricky, inexperienced Windows users might introduce changes and issues into their Windows installation that they don’t want. Even worse, some operations could crash your Windows installation in a way that it becomes inoperable.