The Windows Registry is a directory which is used by the Windows operating system in order to store various options and settings and to expose various kernel-level variables to the user. It stores both system-wide and user-wide settings, providing programmers with a unified method of accessing system information.

Historically, the Windows Registry was first introduced with Windows 95, in order to replace the .ini files which were scattered all around the hard drive. Instead settings being spread through hundreds of files scattered all over the place, they were all gathered in only a handful of binary files. In the latest versions of Windows, the Windows registry is stored in six files holding system-wide settings, plus two other files for each user, holding personal settings.

All the settings in the registry are kept in what geeks like to call a key-value pair. Every entry in the registry has a key, which works like a name, describing what a setting is for. Paired with the key is a unique value, which describes the state of that particular setting or option.

The settings themselves are organized in so-called 'hives', essentially analogous to chapters in a book. A hive contains all the settings that belong to a certain logical category. For instance, the settings contained within HKEY_LOCAL_MACHINE are settings which are general to all the users in the computer, and the hive called HKEY_PERFORMANCE_DATA contains performance-related statistics as provided by the kernel.

A while ago, when the Windows Registry was introduced, it seemed to be a perfect solution. Indeed, in the first months after Windows 95 hit the market, it was universally acclaimed. Problems started appearing shortly after.

First of all, the Windows registry is stored as a binary file. It is not human-readable and the format is fixed, meaning that it can easily get corrupted and can be very difficult to restore. Furthermore, since it is a binary, fixed file format, reading and writing can be relatively slow once the files grow large.

It is quite easy for the files to become very large, because a lot of system information is stored in the registry: file associations, system settings, installation information and so on. As you install software, the registry grows, which is not very helpful.

The biggest problem of the Windows registry is that, despite being quite fragile, it is absolutely vital to the operating system. Windows cannot boot without a healthy registry, and since the registry can get corrupted quite easily, it regularly brings the entire system down.

At the moment, Microsoft is phasing the registry out of use in favor of alternative methods to store program-related settings, while maintaining the registry only for system-wide settings. However, developers are relatively slow to adopt this change, so the Windows Registry as we know it will likely hold out for another few years.

Although there is no magic cure that will make a large registry suddenly become slim, there are ways to keep it tidy and not let it grow larger than it has to. Using a good registry cleaner, such as RegCure or ErrorSmart can ensure that the registry does not get out of control.

Drew specialises in computer security and optimisation. To read his reviews on the top five registry cleaning programs available visit http://www.registry-cleaner-magic.com