The Windows Registry is an essential piece of the Microsoft Windows operating system. Introduced in 1995 with MS Windows 95, the Windows registry is a directory (sometimes called a store) that stores key-value pairs that are essential to the functionality of the operating system. Information contained within the registry includes hardware settings, software settings, user preferences, and more. Every time an application is installed onto a PC or removed, settings in the registry are manipulated. The registry was created to replace the .INI files from the days of DOS (disk operating system) and the original Windows OS. The registry acts as a common store that replaces the need for multiple .INI files scattered across the system, which were often difficult to track.

A word of warning before you attempt to access your registry. Making changes to your registry can cause irreversible damage, such as data loss or the inability for your system to boot. Be sure to [backup your registry] before attempting to make any changes. Note that even backing up the registry may not be a complete safeguard. If you modify a system-critical file that the OS is reliant upon to boot up, your ability to access the registry to restore your backup may be blocked. Proceed with accessing the registry at your own risk!

Microsoft's Windows OS ships with REGEDIT, a tool that allows users and would-be-hackers to access keys and values in the registry directory. To launch REGEDIT, follow the steps below.

• Click the Start Menu in the lower-left of your screen and then click Run (usually the last selection below Search).
• From the Run dialog type Regedit in the textbox and click Ok. The registry editor is now open.

As you can see from the open registry editor, there are 5 top-level folders that all begin with "HKEY_". If you click on the plus symbol (+) on a folder, you'll expand the sub-keys that fall under that specific hive. Next we'll discuss the structure of the registry and the various elements that fall under it.

The registry is broken down into two common elements: keys and values.

Registry keys are the top level folders that appear when you launch regedit. Below each key there may be values or sub-keys. In turn, each sub-key may itself have sub-keys making for a recursive structure. Backslashes are used to indicate levels of hierarchy.

Take the following example:
HKEY_LOCAL_MACHINE\SOFTWARE\Adobe\CommonFiles

In the example above, HKEY_LOCAL_MACHINE is the root key. CommonFiles is the sub-key of Adobe, Adobe is the sub-key of SOFTWARE, and SOFTWARE is the sub-key of the root key HKEY_LOCAL_MACHINE.

Registry values are the name-value pairs of data that is stored within the keys. In the example of the key and sub-key structure, the last element "CommonFiles" contains the name-value pair below:

NAME is the name of the data value to be retrieved. TYPE is the type of data value that is stored. In this case, REG_SZ is a string value. VALUE is the value assigned to that specific element. You can find a complete listing of the data types later in this article.

The registry is split into multiple logical sections at the root level. These root level nodes all begin with "HKEY_" and are referred to as "hives". Hives contains multiple sub-keys (folders) and all have a similar structure. The hive names cannot be modified. Here we take a very brief look at each top-level hive.

HKEY_CLASSES_ROOT
Storage area for information about various registered applications. These include file associations and OLE class IDs required for referencing.

HKEY_CURRENT_USER
Storage area that is specific to the user currently on the system, such as personal preference settings.

HKEY_LOCAL_MACHINE
Storage area for data that is relevant to the operation of the system and is not specific to any one user.

HKEY_USERS
Storage area for each active user in the system.

HKEY_CURRENT_CONFIG
The HKEY_CURRENT_CONFIG storage area is a non-permanent storage area that is regenerated on every system re-boot.

The most common reason to access a Windows registry is for the purpose of cleaning it up. Over time the registry can become bloated with hundreds, even thousands of orphaned and non-functional keys. This bloat results in degraded system performance. As indicated earlier, self-editing of registry files can be a nightmare and may damage your operating system to the point where only a fresh format of the hard drive can fix it. Rather than deal with the frustration, we highly recommend using a registry cleaner application. These applications will scan your system and handle registry keys that are causing system degradation.

Have a look at our comprehensive registry cleaner reviews for our top pick!