The Windows System Registry
As a technician you must be familiar with the System Registry and the tools used to work with it: the Windows Control Panel and the Microsoft Management Console (MMC) in the case of Windows 2000 and Windows XP Professional. You will use them on a regular basis to configure, fine tune, and repair your clients' computers.
Microsoft Windows treats all the devices, device drivers, software services, and applications that use it as objects. The System Registry tracks and makes available to the kernel information on all those objects, hardware, network settings, user preferences, and storage systems.
Windows 3.x made use of initialization (.ini) files to create a bridge between the application and the Windows operating system, as well as a host of other text files such as autoexec.bat and config.sys to manage operations. Some systems had more than 150 files responsible for the operation of the computer and the Windows environment, many of them from third-party providers. This often resulted in erratic and unreliable operation. It also made writing drivers and installation routines much more difficult.
During the development of Windows 3.11 a new file type called reg.dat was introduced into the programming environment. The file was the precursor to the Windows 95 Registry. reg.dat included information used for drag-and-drop operations, OLE (object linking and embedding), and establishing associations between data files and their programs. The reg.dat file was accompanied by its editor, regedit.exe. Reg.dat had a size limit of 64 KB. This limitation was overcome during the development of Windows 95.
During system startup and regular operation, the kernel, system services, background hardware detection devices for Plug-and-Play operation, device drivers, and applications are checking with the Registry to confirm settings. If the Registry becomes corrupt or has the wrong data for an object, it can degrade or even halt system operation. Because of this, Windows provides work tools and safeguards to make it easy to safely modify settings, while ensuring integrity of the Registry files. There are some differences in the Registry structure and tools provided between Windows 95, Windows 98, Windows ME, Windows NT, Windows 2000, and Windows XP but the basics of working with the Registry for both families of Windows are the same.
The Registry is comprised of several files. Hardware- and application-specific settings are stored in one file, user-specific data, such as user profiles, are stored in another and system-specific policies form a third, which can be used to override settings in the other two files. During system operation, the active elements of the Registry are brought into RAM as a single repository.