The Windows Registry is a hierarchical database for storing many kinds of system and application settings.Prior to the Registry, files in the form of text files were commonly used for storing these settings.
Hardware, security and security accounts manager subkeys can't be edited.
It is not advised to manully alter the rest as it might result in a system crash.
On the other hand, the Windows Registry uses one logical repository that is able to store user-specific settings.
According to Microsoft, there are several advantages over the obsolete files like faster parsing, backup or restoration.
The Registry is based on the two basic elements, keys and values and the entire structure is a tree with several root elements that slightly differ depending on the version of Windows you are currently using.