How can you backup and restore the Registry?

Maintaining the Registry

Windows 95
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 the USER.DAT file.

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.

Windows 98
Microsoft Windows 98 automatically creates a backup copy of the registry every time Windows starts, in addition to this you can manually create a backup using the Registry Checker utility by running SCANREGW.EXE from Start | Run menu.

What to do if you get a Corrupted Registry
Windows 95, 98 and NT all have a simple registry backup mechanism that is quite reliable, although you should never simply rely on it, remember to always make a backup first!

Windows 95
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:
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* Click the Start button, and then click Shut Down.

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

* Change to your Windows directory. For example, if your Windows directory is c:\windows, you would type the following:

cd c:\windows

* 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

* 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.

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

How can I clean out old data from the Registry?
Although it's possible to manually go through the Registry and delete unwanted entries, Microsoft provides a 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, it removes them from the Windows Registry after having recording those entries in the Undo.Reg file.