The Registry, when viewed in its entirety, is split into five main sections, or groups. This helps organize the different keys and folder in the Registry to make them easily navigable.
1. HKEY_CLASSES_ROOT (HKCR):
This section stores information about registered applications, OLE Object Class IDs, and file associations. Sometimes you may see it abbreviated to HKCR. Should a subkey be added that duplicates a key that already exists in HKEY_CURRENT_USER\Software\Classes, Windows will use the HKEY_CURRENT_USER\Software\Classes key as its master.
2. HKEY_CURRENT_USER (HKCU)
This section contains the configuration options for the currently signed-in user’s profile,
including the disk locations for user folders, control panel settings, and specific app
configuration settings.
3. HKEY_LOCAL_MACHINE (HKLM)
As you might expect, this key contains all the settings specific to the PC on which
Windows is installed. It contains the subkey files SAM, SECURITY, SYSTEM, and SOFTWARE
that I listed earlier. A fifth file, HARDWARE, is created afresh each time the PC starts, and
contains information about currently detected plug-and-play hardware.
This key also contains the files COMPONENTS and BCD, which can be found in the
%systemroot%\System 32\Config\ folder, and which contain information specific to the
PC’s boot configuration data.
4. HKEY_USERS (HKU)
The HKU key contains settings and options for the currently-loaded user profile. You
cannot access settings for any user account other than the currently signed-in user
through these keys.
5. HKEY_CURRENT_CONFIG (HKCC)
Last, the HKCC keys contain information gathered when the PC starts and Windows loads.
This information is relevant only to the current powered-session and is discarded when
the PC is switched off.
6. HKEY_PERFORMANCE_DATA
This section is invisible when using the Windows Registry Editor. It contains runtime and
performance data that is provided by the Windows kernel, drivers, apps, and services. It is
discarded when the PC is switched off and is rebuilt at the next boot.
>> Continue to Registry Keys and Values Part #2