It is important to understand what the Registry is, why it exists, and the types of information it contains.  Virtually everything done in Windows refers to or is recorded into the Registry.  A program called RegMon by Sysinternals can be used to display registry activity in real time.  After running this program it is apparent that registry access barely remains idle.  The Registry is referenced in one way or another with every action taken by the user.

The Microsoft knowledge database and also the Microsoft Computer Dictionary, Fifth Edition, define the registry as:

A central hierarchical database used in Microsoft Windows 9x, Windows CE, Windows NT, and Windows 2000 used to store information necessary to configure the system for one or more users, applications and hardware devices.

The Registry was first introduced with Windows 95 and has been incorporated into many Microsoft operating systems since.  Although some versions slightly differ, they all are essentially composed of the same structure and serve the main purpose as a configuration database.  The Registry replaces configuration files that were used in MS-DOS, such as config.sys and autoexec.bat.  The primary purpose of config.sys was to load device drivers and the primary purposes of autoexec.bat was to run startup programs and set environment variables – the Registry now handles these functions.  In addition to replacing DOS configuration files, the Registry also replaces text-based initialization (.ini) files that were introduced in Windows 3.0.  The .ini files – specifically win.ini and system.ini – store user settings and operating system parameters.

This very basic history of the Windows Registry, why it was implemented, and some of its functions are the core fundaments of understanding the structure and what each part of the Registry pertains to.