Windows registry cleaner
Windows registry is a database used by the computer to store information needed for its smooth running.
Many different pieces of information are stored in the database, some relate to hardware others to software.
Problems can arise when programs are removed and hardware no longer connected.
The registry may still contain snippets of information that are no longer needed.
The more you install and uninstall programs or delete files from your computer the more likely you are to have 
registry that contains unused and obsolete information.
Whilst the effects of this can slow a computer down, I do feel that this is overdone, probably by the vendors of software that relate to the windows register.
If you have a computer that runs rather slowly, the windows registry should be one of the later tune ups that you do.
Spy ware and other programs that load up without your consent can grind your computer to almost to a halt.
Keeping your registry in good order is definitely high on the list of maintenance tasks but should not be done in isolation without considering the other and often more important (as far as computer speed is concerned) tasks
Anti virus, Anti spyware, removing unwanted programs that run on start up should be achieved before a registry tune up.
The structure of the registry - If you wish to know more about the registry windows provides the program REGEDIT.EXE from the start/run menu.

IT IS NOT RECOMMENDED THAT YOU MAKE ANY ADJUSTMENTS WITH THIS PROGRAM

When you run this program you can the registry is divided up into a tree 
 
The HKEY_CLASSES_ROOT  is an alias of the HKEY_LOCAL_MACHINE\Software\Classes.

This means that the contents in HKEY_LOCAL_MACHINE\Software\Classes
are also available again in HKEY_CLASSES_ROOT

This data contains a reference to the file extensions and their associated applications

You can manually change this by changing the file association provided with windows controls.

Open windows explorer -- > tools --> folder options
The files types is shown opposite 

Making changes using this method allows the user an easy access to the registry that will not have the disastrous results should a mistake be made when changing the registry direct

 .

HKEY_CURRENT_USER

 
 


The HKEY_CURRENT_USER is an alias of the HKEY_USERS.

This means that the contents in HKEY_CURRENT_USER
are also available again in HKEY_USERS.

This may not seem immediately obvious because the data is held in SIDS (security identifiiers (shown opposite), these are used to avoid hacking attempts to gain access to users settings.

This root key contains information specific to the user, if the user profiles are being used, this relates to the user who is currently logged on.

The contents of the  HKEY_CURRENT_USER are shown (opposite)
The settings control how the computer is set up when an individual users logs in.

AppEvents - Details of the sounds which the user as associated with the system.

Control panel - Settings that can be made from the control panel 
Color schemes, screen savers, mouse speed etc.

Keyboard Layout -  Contains settings from the Language tab in the Keyboard properties. Also contains a key named preload , this contains holds a key for each installed keyboard layout.

These keys act as pointers to 
HKEY_LOCAL_MACHINE
\System\CurrentControlSet\Control\Keyboard Layouts.

The keyboard layouts are listed for each individual counties.

It is recommended that you open regedit and go into and see these setting for yourself.

 
The final first level sub-keys I intend to examine is the also the largest, that is the software (left).
There is a list in alphabetical order for each vendor that as software installed on the machine.
The sub keys in the vendors application can be used for preferences , history, color setup etc.
 HKEY_LOCAL_MACHINE
Contains computer specific information.
The first sub-key is the SYSTEM sub-key containing 
all the hardware programs that have been set up for the machine 
Each hardware key these are named 0001,0002

The device map contains details of the printers, videos and other devices in the profile.

Opening ControlSet001  reveals the first level sub-key Enum
This holds information about all the devices and peripherals.
Details such as drive ID and manufacturer, USB information.
Enum contains a key for each class of hardware.
These vary according to the installed devices but will typically include Plug and play, drives, floppy drives, printers etc.

The current control set stores information needed at boot time 
which in turn contains 2 keys Services and Control.
The control contains information needed at boot time.
These include file system settings, multimedia, resources, descriptions of network providers,.
Inside the CurrentControlSet the sub-key Services lists the device drivers which windows must load during booting. 

 
The hardware first level key contains details about the CPU, serial ports and floating-point processor.
The security sub-key provides security provider details.
HKEY_LOCAL_MACHINE subkey SOFTWARE
This subkey closely parallels the software subkey in HKEY_CURRENT_USER.

However the HKEY_CURRENT_USER.\SOFTWARE refers to user related settings for the application.

HKEY_LOCAL_MACHINE subkey SOFTWARE contains user settings for the installed applications.

Example of this would be for powerpoint, the 
HKEY_CURRENT_USER.\SOFTWARE would contain the currents users preference for powerpont.
HKEY_LOCAL_MACHINE\SOFTWARE would contain applications directories, details of installed filters etc.
 

 
The .DEFAULT provides the default values for a new user.

If the profiles are not enabled the .default store the values for the actual user.

When a user logs on, windows creates the HKEY_CURRENT_USER alias from profile that it corresponds to.
The contents of the profile key  HKEY_USER are identical to that  the profile key within HKEY_CURRENT_USER
(mentioned previously)
 
HKEY_CURRENT_CONFIG

Has mentioned previously the hardware/software profiles are 
HKEY_LOCAL_MACHINE.

The HKEY_CURRENT_CONFIG is an alias for
 

HKEY_LOCAL_MACHINE.\System\CurrentControlSet\
HardwareProfiles\

This can be seen opposite.

The Software and System folders appear in both places.