Every operating system and application needs a place to store its configuration settings and user preferences. With the computers becoming more and more complex, so have the methods of storing this data. Earlier there were only few settings needed by MS-DOS and that were stored in the plain text file CONFIG.SYS. DOS programs had to make their own arrangements for storing user settings. Windows originally used INI files - text files organised in a simple format that could be read and written using special routines available to Windows programs. Windows had one configuration file, SYSTEM.INI, which was used for all the internal settings plus another, WIN.INI, for user preferences. Each application had an INI file, too, usually named after itself.
This system worked pretty well, and is still used by some Windows programs, but it turned out to have a few disadvantages. INI files were slow to access and limited in size to 64Kb. There was also just one INI file per program per computer, making it difficult to have different settings for each user of a computer.
So for Windows NT and Windows 95 Microsoft introduced the Registry. You can think of the Registry as a database for storing and accessing configuration data. Like all good databases the Registry can store different types of data. It is organised for fast and efficient access. Data is stored in a hierarchical manner rather like the folders on a hard disk. Registry data that is currently in use is cached in memory to provide better performance.
