In Windows 3.1 and Windows 3.11 versions of windows which are now obsolete there were many INI files used by the Operating System. These INI files containted details of different hardware and applications installed in the computer.
But in Windows 95, Microsoft introduced the concept of 'Registry'. In these registries, windows stored details and settings of all the hardware and applications.
All the windows versions starting from Windows 95 followed this Registry style. Windows 98, ME, NT, 2000 and XP use these registries.
In today's Windows Operating System, Registries play an important role. If due to some reason these registries get corrupted then the whole computer becomes unusable and cannot even boot the system. If you had the backup of registries then you can restore these registries and make your computer function again.
You never know when these registries get corrupted. Therefore it is a good practice to backup your registries every now and then, so that when required you can use this backup to restore your registry settings.
Registry in Windows 95/98/ME
In Windows 95 and 98, System.dat and User.dat are two important files. The reason is these two files are the registries. In Windows ME a third file namely Classes.dat was included as part of the registry.
These three files are usually located in the 'Windows' folder. So if you use Windows explorer, goto 'Windows' folder and copy these three files to another folder then the backup of registry is done.
Microsoft has provided an utility for backing up registries called ERD. In your Windows CD this utility is there.
Moreover, Windows 95,98 and ME backs up the registry on startup.
Registry in Windows NT, Windows 2000 and Windows XP.
Those Windows Os that are based on the NT Kernel such as Windows NT/2000/XP do not backup registry on its own. Therefore you have to backup manually if you are using one of these windows versions.
It is not an easy task to backup registry in Windows NT/2000/XP. There are many files such as Default, Sam, Security, Software and System that constitute registries. They are found in the System32/Config folder. Since these files are used by the OS, you cannot copy these files.
In Windows NT you can use Regback utility to backup registry and Regrest utility to restore back the registry. In Windows 2000 you can use the NTBACKUP utility to backup and restore registries.
In Windows XP you can use System Restore utility to backup and restore utilities.
In Windows NT/2000/XP chances of registry getting corrupted is very less. Maybe that is the reason why Microsoft does not provide easier methods to backup and restore registries in these versions of Windows.
http://home.t-online.de/home/lars.hederer/erunt is a free software that you can download and use to backup and restore registries in Windows NT/2000/XP.