The Windows Registry is the database within your computer that stores the settings and options used on your computer. The information stored pertains to a whole host of things, like the hardware, operating system software, much of the non-operating system software, user preferences, and more. In fact, any time you make a change in your Control Panel, file associations, system policies, or software, you create an entry in the registry.

Although earlier versions of Windows didn't utilize the registry system, the 32-bit, 64-bit, and Mobile versions do. The registry system was created to clean up the huge number of INI files previously needed to store configuration settings. Before the registry was created, INI files were stored all over the computer, in so many different places that they were hard to keep track of.

The registry structure is made up of many sections, referred to as "keys." The keys are named according to the definitions that are used to access them. All of the keys start with "HKEY," which stands for "Handle to Key." The abbreviations for the keys are usually up to four letters long and begin with HK. So, for example, the name for the HKEY_CLASSES_ROOT key, which stores information about the registered applications, has the abbreviation "HKCR." Each of these keys may have several sub-keys.

There are a number of good reasons for implementing the registry system. One useful feature is that it allows the information for machine configuration to be kept separate from user configuration. Because of this, programs can more easily follow configurations specific to each user instead of having system-wide configuration.

The registry is much easier to back up than scattered INI files. It also allows changes and readings to be tracked, which is extremely useful when debugging a problem.

Although there are many good reasons for the Windows Registry system, unfortunately, it has its problems, too. For one thing, if the registry should become damaged, the system may be completely unable to boot up. When the problem is especially severe, there may be no way to repair the problem at all, making it necessary to replace the computer.

Another issue is that some applications use the registry to store and retrieve settings. When this is the case, the application may not be usable on a portable device used to carry the application from system to system.

One of the most common and annoying problems the registry system has created is a general gumming up of the operating system so that it becomes sluggish. Because virtually any change creates a registry entry, even an unsuccessful uninstall process can place entries on the registry. As a result, a lot of space is eaten up on the hard drive.

The registry can be manually edited. However, this can be a very difficult and risky procedure. The manual editing process requires the user to run regedit.exe or regedt32.exe in the Windows directory. Only advanced users should attempt to do this because making a mistake could cause damage that can't be fixed. If you do decide to try editing your registry, it's absolutely imperative that you make a back up first.

All in all, the registry is a pretty complicated concept for most people. Unfortunately, that means it causes frustration and complications. Registry problems are more common in older versions of the Windows operating system. However, they do occur in Windows NT and XP as well. There are tools available to assist with editing and cleaning the registry, and they may be the best way to handle your registry problems without causing undue damage to your system.