The A+ Certification & PC Repair Handbook (Charles River Media Networking/Security)

The Windows 9x Registry, as well as the registries implemented in Windows NT and Windows 2000, are hierarchical databases made up of special Registry Keys that hold most of the operating system’s software, hardware, and application settings. The Windows 9x Registry was developed with the intention of replacing the dependency on the WIN.INI, SYSTEM.INI, AUTOEXEC.BAT, and CONFIG.SYS files for loading system initialization, device, and user environment settings.

The Windows Registry is a sort of common ground that is used to link applications, programs, objects, and settings. Windows 3x utilized the Object Linking and Embedding (OLE) functionality of a binary file called REG.DAT. Object linking is a method whereby a program or application can use an object or part of a program that is created by another program.

The Windows 9x Registry is made up of two important files called USER.DAT and SYSTEM.DAT. These files are stored as hidden, read-only system files in the C:\WINDOWS directory. The USER.DAT file stores user-related Registry settings, such as user preferences and desktop settings. The SYSTEM.DAT file is used to store device settings. Every time Windows 9x is started, the system looks for USER.DAT and SYSTEM.DAT to create and load the operating system’s environment and related device settings. If these two files are not found, the system automatically looks for the files USER.DA0 and SYSTEM.DA0, which are backup copies of the two main Registry files maintained by the operating system.

Viewing and Modifying the Registry

Warning! Great care should be taken when entering or making changes to the Windows 9x Registry—or any Registry, for that matter. Making improper changes to the binary values stored in the Registry or installing certain software that can cause Registry corruption may leave you with a system that is unstable at best. If your users or customers observe strange happenings, such as a missing taskbar, blank icons, or programs that won’t load, they are most likely experiencing a corrupt Registry or virus activity. You should always manually back up the Registry before making any changes to it. Windows 98 comes with an excellent tool called Registry Checker that works well for this purpose. If your Registry becomes corrupted, you can use the SCANREG utility from a DOS prompt to restore a backup copy of the Registry. The command used for restoring a Registry from a DOS prompt is SCANREG/RESTORE.

Using the Windows 9x Device Manager and Control Panel options to change settings and devices is considered the safest way for most users to make edits to the Registry. It is more common for advanced users to edit the Registry in Windows 9x with the REGEDIT.EXE program stored in C:\WINDOWS in Windows 9x by default. To enter the Windows 95 Registry, simply click Start > Run, and then type in “REGEDIT” on the Open command line. The window shown in Figure 24.1 will appear.

Figure 24.1: The Windows 9x Registry.

The six major Registry keys are displayed in Figure 24.1. Each of these keys and their subkeys are responsible for holding system and device settings and information. The current A+ Operating Systems Technologies exam will expect you to be familiar with the techniques used to edit, backup, and restore the Windows 9x Registry. For the exam’s purposes, you should know the functionality associated with HKEY_LOCAL_MACHINE.

The functions of each of the six major Registry HKEYs are as follows:

HKEY_CLASSES_ROOT: Stores file extensions and OLE information.

HKEY_CURRENT_USER: Stores all information as it pertains to the specific user who is currently logged into the local system.

HKEY_LOCAL_MACHINE: Stores all the software, hardware, and operating system settings of all configurations used on the system.

HKEY_USERS: Stores all user preferences for each separate user with a profile located on the local system.

HKEY_CURRENT_CONFIG: Stores the current hardware profile for peripheral devices, such as monitors and printers.

HKEY_DYN_DATA: Stores all current performance data, such as the results of running System Monitor.