The physical files that make up the registry are stored differently depending on your version of Windows; under Windows 95 & 98 it is contained in two hidden files in your Windows directory, called USER.DAT and SYSTEM.DAT, while under Windows NT the files are contained seperately in the "Windows / System32 / Config" directory.

The Registry Editor (REGEDIT.EXE) is included with most version of Windows (although you won't find it on the Start Menu) it enables you to view, search and edit the data within of the Registry. There are several methods for starting the Registry Editor, the simplest is to click on the START button, then select RUN, and it the OPEN: box type "regedit".

This can be done by simply right-clicking on a blank area of your desktop, selecting New, then Shortcut, then in the Command line box enter "regedit.exe" and click Next, enter a friendly name (e.g. 'Registry Editor') then click Finish and Presto!

Once you have started the Regedit you will notice that on the left side there is a tree with folders, and on the right the contents (values) of the currently selected folder.

To expand a certain branch (see the structure of the registry below), click on the plus sign [+] to the left of any folder, or just double-click on the folder. To display the contents of a key (folder), just click the desired key, and look at the values listed on the right side. You can add a new key or value by selecting New from the Edit menu, or by right-clicking your mouse. And you can rename any value and almost any key with the same method used to rename files; right-click on an object and click rename, or click on it twice (slowly), or just press F2 on the keyboard. Lastly, you can delete a key or value by clicking on it, and pressing Delete on the keyboard, or by right-clicking on it, and choosing Delete.

Note: it is always a good idea to backup your registry (see below) before making any changes to it. It can be intimidating to a new user, and there is always the possibility of changing or deleting a vitual setting causing you to have to reinstall the whole operating system. It's much better to be safe than sorry!

Regedit has a number of command line options to help automate it's use in either batch files or from the command prompt. Listed below are some of the options, please note the some of the functions are operating system specific.

filename Import.reg file into the registry

/s Don't display dialog box when importing .reg files

/e Export registry file e.g. regedit /e filename.reg HKEY_LOCAL_MACHINE\SYSTEM

/L:system Specify the location of the system.dat to use

/R:user Specify the location of the user.dat to use

/C Compress [filename] (Windows 98)

The Registry has a hierarchal structure, although it looks complicated the structure is similar to the directory structure on your hard disk, with Regedit being similar to Windows Explorer. Each main branch (denoted by a folder icon in the Registry Editor, see below) is called a Hive, and Hives contains Keys. Each key can contain other keys (sometimes referred to as sub-keys), as well as Values. The values contain the actual information stored in the Registry. There are three types of values; String, Binary, and DWORD - the use of these depends upon the context. There are six main branches, each containing a specific portion of the information stored in the Registry. They are as follows:

HKEY_CLASSES_ROOT : This branch contains all of your file association types, OLE information and shortcut data.

HKEY_CURRENT_USER : This branch links to the section of HKEY_USERS appropriate for the user currently logged onto the PC.

HKEY_LOCAL_MACHINE : This branch contains computer specific information about the type of hardware, software, and other preferences on a given PC, this information is used for all users who log onto this computer.

HKEY_USERS : This branch contains individual preferences for each user of the computer, each user is represented by a SID sub-key located under the main branch.

HKEY_CURRENT_CONFIG : This branch links to the section of HKEY_LOCAL_MACHINE appropriate for the current hardware configuration.

HKEY_DYN_DATA : This branch points to the part of HKEY_LOCAL_MACHINE, for use with the Plug-&-Play features of Windows, this section is dymanic and will change as devices are added and removed from the system.

Microsoft included a utility on the Windows 95 CD-ROM that lets you create backups of the Registry on your computer. The Microsoft Configuration Backup program, CFGBACK.EXE, can be found in the \Other\Misc\Cfgback directory on the Windows 95 CD-ROM. This utility lets you create up to nine different backup copies of the Registry, which it stores, with the extension RBK, in your \Windows directory. If your system is set up for multiple users, CFGBACK.EXE won't back up USER.DAT.

After you have backed up your Registry, you can copy the RBK file onto a floppy disk for safekeeping. However, to restore from a backup, the RBK file must reside in the \Windows directory. Windows 95 stores the backups in compressed form, which you can then restore only by using the CFGBACK.EXE utility.

A useful feature of the Registry Editor is it's ability to import and export registry settings to a text file, this text file, with the .REG extension, can then be saved or shared with other people to easily modify local registry settings. You can see the layout of these text files by simply exporting a key to a test file and opening it in Notepad, to do this using the Registry Editor select a key, then from the "Registry" menu choose "Export Registry File...", choose a filename and save. If you open this file in notepad you will see a file similar to the example below:

REGEDIT4

[HKEY_LOCAL_MACHINE\SYSTEM\Setup]

"SetupType"=dword:00000000

"CmdLine"="setup -newsetup"

"SystemPrefix"=hex:c5,0b,00,00,00,40,36,02

The layout is quite simple, REGEDIT4 indicated the file type, [HKEY_LOCAL_MACHINE\SYSTEM\Setup] indicated the key the values are from, "SetupType"=dword:00000000 are the values themselves the portion after the "=" will vary depending on the type of value they are; String, Binary, or DWORD.

So by simply editing this file to make the changes you want, it can then be easily distributed and all that need to be done is to double-click, or choose "Import" from the Registry menu, for the settings to be added to the system Registry (see Regedit Command Line Options above).

Firstly don't try ringing Microsoft Technical Support, they most probably won't help you. Luckly though both Windows 95, 98 and NT have a simple registry backup mechanism that is pretty reliable, although don't count on it, always make a backup first!

In the Windows directory there are several hidden files, four of these will be SYSTEM.DAT & USER.DAT, your current registry, and SYSTEM.DA0 & USER.DA0, a backup of your registry. Windows 9x has a nice reature in that every time it appears to start successfully it will copy the registry over these backup files, so just in case something goes wrong can can restore it to a known good state. To restore the registry follow these instruction:

1. Click the Start button, and then click Shut Down.

2. Click Restart The Computer In MS-DOS Mode, then click Yes.

3. Change to your Windows directory. For example, if your Windows directory is C:\Windows, you would type the following:

cd C:\Windows

4. Type the following commands, pressing ENTER after each one.

(Note that SYSTEM.DA0 and USER.DA0 contain the number zero.)

attrib -h -r -s system.dat

attrib -h -r -s system.da0

copy system.da0 system.dat

attrib -h -r -s user.dat

attrib -h -r -s user.da0

copy user.da0 user.dat

5. Restart your computer.

Following this procedure will restore your registry to its state when you last successfully started your computer.

If all else fails, there is a file on your hard disk named SYSTEM.1ST that was created when Windows 95 was first successfully installed. If necessary you could also change the file attributes of this file from read-only and hidden to archive to copy the file to C:\WINDOWS\SYSTEM.DAT.

On Windows NT you can use either the "Last Known Good" option, or RDISK to restore to registry to a stable working configuration.

Although it's possible to manually go through the Registry and delete unwanted entries, Microsoft provides a nifty tool to automate the process, the program is called RegClean. RegClean analyzes Windows Registry keys stored in a common location in the Windows Registry. It finds keys that contain erroneous values, and after recording those entries in the Undo.Reg file, it removes them from the Windows Registry.