Logical Registry Hive

The Registry has many thousands of settings; in fact, it often has tens of thousands of them. They are organized into five main Registry sections, called Registry hives. Think of each hive as a root directory. Each of the hives has a different purpose. When you start to delve into the Registry, you may notice that many of the settings seem to be exact duplicates of one another—in other words, settings in one hive mirror the settings in another hive. In fact, frequently one set of settings is merely an alias (called a symbolic link) of another, so that when you change those settings in one place, the changes are made in both hives.

The hives themselves are stored in the C:\Windows\system32\config and C:\Documents and Settings\{username} files.

Following are the five hives and what each does:

HKEY_CLASSES_ROOT
This hive contains information about file types, filename extensions, and similar information. It instructs XP how to handle every different file type and controls basic user interface options, such as double-clicking and context menus. This hive also includes class definitions (hence the word "CLASSES" in its name) of unique objects, such as file types or OLE objects. Frequently, classes associated with file types contain the Shell subkey, which defines actions, such as opening and printing, that can be taken with that file type.

HKEY_CURRENT_USER
This hive contains configuration information about the system setup of the user that is currently logged into XP. It controls the current user's Desktop, as well as XP's specific appearance and behavior for the current user. This hive also manages network connections and connections to devices such as printers, personal preferences such as screen colors, as well as security rights. Also included in this hive are Security Identifiers (SIDs), which uniquely identify users of the PC and which have information about each user's rights, settings, and preferences.

HKEY_LOCAL_MACHINE
This hive contains information about the computer itself, as well as about the operating system. It includes specific details about all hardware, including keyboard, printer ports, storage—the entire hardware setup. In addition, it has information about security, installed software, system startup, drivers, services, and the machine's specific XP configuration.

HKEY_USERS
This hive contains information about every user profile on the system.

HKEY_CURRENT_CONFIG
This hive contains information about the current hardware configuration of the system, in the same way that HKEY_CURRENT_USER contains information about the current user of the system.