The windows registry is simply a database of settings and options for the Windows operating system, its hardware and installed applications. It contains a rather critical set of information entries that a PC simply can not do without. The registry stores information that the OS continually references during normal operations to reach and load applications, user profiles and preferences, property settings for files and folders, hardware information, assigned ports, licenses etc.

From a more technical orientation, we look at what the registry really is as we look at it via regedit, the built in editor for the windows registry.

Your PC's registry is divided into hives, keys, subkeys and values. An example of a registry hive is HKEY_LOCAL_MACHINE\Software. In it you'll find a large number of keys, which in fact look like folders. This particular hive contains some of the most critical data on your PC, it holds references to all the software programs installed on your PC, should something unexpectedly change with one of these keys causing serious problems to your PC, a registry cleaner is the most effective fix for your registry.

The registry key values change according to the application, so these should not change unless you're specifically sure of what you're doing. The regedit tool looks friendly but it can be deadly.

The physical files that make up the registry are kept in different areas depending on the version of Windows you're running. Windows 95 & 98 contained in two hidden files in the Windows directory, called USER.DAT and SYSTEM.DAT. Windows ME had an additional CLASSES.DAT file. Then on Windows NT/2000 the files were contained separately in the %SystemRoot%\System32\Config directory. These files can not be edited directly, in order to do that you would use regedit to make any changes.

Structure of the Windows Registry

As mentioned earlier, there are a few components to the registry, beginning with hives. The following is a list of those components and what category of information they contain.

• HKEY_CURRENT_USER (HKCU)
  This hive contains all preferences and configurations for the user that is currently logged in, meaning that each user has their own HKCU hive when they log into a PC.
• HKEY_LOCAL_MACHINE (HKLM)
  This hive contains all system related information in terms of OS, hardware and software applications installed. This information remains the same for all users.
• HKEY_CLASSES_ROOT (HKCR)
  Here' you'll find information for the core user interface, such as file associations and shortcuts.
• HKEY_USERS (HKU)
  This hive keeps user information for every user that has an account on a PC
• HKEY_CURRENT_CONFIG (HKCC)
  This hive holds information on current hardware configuration. This key is an extension of the HKLM.
• HKEY_DYN_DATA (HKDD)
  This hive only exists on Windows 95/98/ME. Containing hardware plug and play information, this hive is also linked to the HKLM.

The windows registry, in addition to these hives will contain keys and subkeys that hold values, that the windows operating system reads continually to figure out specific settings and options. It is never recommended to edit the windows registry unless you know what you're doing it is simply to easy to make a mistake and end up with registry corruption.