Tutorial 5: What is Windows registry (Registry Keys)

Reason of this project:
I wrote this tutorial in order to help the hundred of programmers searching on the web for Windows registry.
This is an like introduction, if you are seeking how to use and deploy the registry keys with Vb.net, just see the next tutorial (It'll be tutorial 6).
In this tutorial I'll show what is the windows registry system and why use it.

Project details:
1- What is Windows registry and why use it
2- How to read, write and change the registry
3- HIVES and their use
4- Definition of registry values

1- What is Windows registry and why use it.

You can compare the Windows registry to a database. It stores informations related to Windows and other installed application on your system, but also Hardware.
Think now if someone need to change the computer name via programming. How can he do this?
Programmers can think of files (text files) to store the computer and windows information. But when file get big and heavy, Database will be more secure. And then they had (Windows builder) the choice of a database "Windows Registry".
Microsoft Dot Net Frame 1.1 and higher have implemented a great solution for registry on their classes. This will replace the hard work and long lines of code that programmers have to write if they are using Visual Studio 6.0 for example.

2- How to read, write and change the registry

Windows has a wonderful tool on it, named "Registry Editor". But you won't find it, unless you open the System32 folder on the Windows folder.
But we can easily run it through the execute command it the start menu. Just type "regedit" (without quotes).
Now the registry editor will open.
Please before doing any changes on your registry make a backup.
To do a windows registry backup: File > Export > Give a name for the file and select the All option box.
The backup may block your pc from working for a short period of time.
You'll see that there are 5 folder. Those are the main folder (named hives) and you can't add another main folder.
Now you can select any folder and right click on it, then add a new sub-folder or value.
By selecting any folder and right clicking, you'll find a list of action that you can do.
If the action is blended (made not selectable), then either it's impossible or you don't have the rights to do this action.
You need administrator rights to change registry keys.

3- HIVES (main registry folders) and their use

The registry is split into a number of logical sections named "hives", those are the top main folder that can added, edited or renamed.
They all start with "HKEY" prefix.

HKEY_CLASSES_ROOT
Stores information about registered applications, such as Associations from File Extensions and OLE Object Class ID's tying them to the applications used to handle these items.
HKEY_CURRENT_USER
Stores settings that are specific to the currently logged-in user. The HKCU key is a link to the subkey of HKEY_USERS that corresponds to the user; the same information is reflected in both locations. On Windows-NT based systems, each users' settings are stored in their own files called NTUSER.DAT and USRCLASS.DAT inside their own documents and settings subfolder.
HKEY_LOCAL_MACHINE
Stores settings that are general to all users on the computer. On NT-based versions of Windows, HKLM contains four subkeys, SAM, SECURITY, SOFTWARE and SYSTEM, that are found within their respective files located in the %SystemRoot%\System32\Config folder. A fifth subkey, HARDWARE, is volatile and is created dynamically, and as such is not stored in a file. Information about system hardware drivers and services are located under the SYSTEM subkey, whilst the SOFTWARE subkey contains software and windows settings.
HKEY_USERS
Contains subkeys corresponding to the HKEY_CURRENT_USER keys for each user registered on the machine.
HKEY_CURRENT_CONFIG
Contains information gathered at runtime; information stored in this key is not permanently stored on disk, but rather regenerated at boot time.

4- Definition of registry values

Binary Value
REG_BINARY
Raw binary data. Most hardware component information is stored as binary data and is displayed in Registry Editor in hexadecimal format.
DWORD Value
REG_DWORD
Data represented by a number that is 4 bytes long (a 32-bit integer). Many parameters for device drivers and services are this type and are displayed in Registry Editor in binary, hexadecimal, or decimal format. Related values are DWORD_LITTLE_ENDIAN (least significant byte is at the lowest address) and REG_DWORD_BIG_ENDIAN (least significant byte is at the highest address).
Expandable String Value
REG_EXPAND_SZ
A variable-length data string. This data type includes variables that are resolved when a program or service uses the data.
Multi-String Value
REG_MULTI_SZ
A multiple string. Values that contain lists or multiple values in a form that people can read are generally this type. Entries are separated by spaces, commas, or other marks.
String Value
REG_SZ
A fixed-length text string.
Binary Value
REG_RESOURCE_LIST
A series of nested arrays that is designed to store a resource list that is used by a hardware device driver or one of the physical devices it controls. This data is detected and written in the \ResourceMap tree by the system and is displayed in Registry Editor in hexadecimal format as a Binary Value.
Binary Value
REG_RESOURCE_REQUIREMENTS_LIST
A series of nested arrays that is designed to store a device driver's list of possible hardware resources the driver or one of the physical devices it controls can use. The system writes a subset of this list in the \ResourceMap tree. This data is detected by the system and is displayed in Registry Editor in hexadecimal format as a Binary Value.
Binary Value
REG_FULL_RESOURCE_DESCRIPTOR
A series of nested arrays that is designed to store a resource list that is used by a physical hardware device. This data is detected and written in the \HardwareDescription tree by the system and is displayed in Registry Editor in hexadecimal format as a Binary Value.
None
REG_NONE
Data without any particular type. This data is written to the registry by the system or applications and is displayed in Registry Editor in hexadecimal format as a Binary Value
Link
REG_LINK
A Unicode string naming a symbolic link.
QWORD Value
REG_QWORD
Data represented by a number that is a 64-bit integer. This data is displayed in Registry Editor as a Binary Value and was introduced in Windows 2000.

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