 Performance
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PC Advice
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Windows Registry |
The Registry is a Windows component that inspires much fear among novice users, and occasional annoyance for experienced techies. It appeared as of Windows 95, and was designed to eliminate the massive, confusing mess of .INI files that were then used by individual user- and system-level applications to store configuration and startup data. Life became difficult when multiple applications tried to store a "STARTUP.INI" file in, for instance, C:\WINDOWS\ at the same time. One would overwrite the other's settings, causing failures and confusion, so Microsoft introduced the Registry as a single-source location for all such information. Additionally, the Registry stores the following:
- Hardware settings
- Preference information for individual users, as well as global preferences for all users on the system.
- Application registration data, as well as file associations. The latter is used to tell Windows what application is used to open, for instance, PDF documents or .AVI files.
There are five "hives" of data in the Registry:
- HKEY_CLASSES_ROOT: this stores file associations, application data, and OLE (Object Linking and Embedding) information
- HKEY_CURRENT_USER: holds information related to the currently logged-in user, including desktop preferences, available applications, Windows settings, etc.
- HKEY_LOCAL_MACHINE: is the location where data related to all users on the system is stored. It also retains data related to system hardware, such as IRQ data, modem or networking settings, and video subsystem settings.
- HKEY_USERS: is more or less a mirror of HKEY_CURRENT_USER
- HKEY_CURRENT_CONFIG: involves runtime information generated and tracked during a given boot lifetime. This information isn't stored on disk, but is recreated every time Windows reboots.
For the most part, the Registry is managed automatically by the OS (it's written to whenever hardware or applications are modified, removed, or installed, for instance), but can be edited manually by running regedit.exe or regedt32.exe, both of which are included with the OS. Usually these don't appear on the Programs listing, and are generally started either from a DOS command line or via the Start -> Run option.
It is generally recommended that only experienced users edit the Registry manually, since poorly managed changes to system settings can irreversibly damage a Windows installation. It's possible to render a machine unbootable by changing or removing settings, so even experienced users tend to make backups of Registry data prior to editing sessions. It's also possible to export the entire Registry, or only selected keys, to human-readable text files using the regedit /s option, which takes a file name as a parameter and writes the settings to that file.
As of Windows XP, you can also make manual changes using reg.exe, which can query, add, remove, and perform numerous other functions without displaying the full regedit interface.
Whole books have been written on this subject, and a great deal of additional (often incorrect) information is available on the Web. There's a very good introduction to the Registry on Wikipedia, which provides additional detail and history regarding the development and use of this system. Most users will never need to alter or manage these settings manually, but it's useful to know why this system exists and what its functions are. It's not a subsystem that one should approach with a cavalier attitude for obvious reasons (a friend once deleted the Registry files and wondered why his machine refused to boot!), but a general understanding is useful. It provides some insight into Windows internals, and might help you determine where an error or configuration problem is originating.
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