Higly recommended but rarely done
Emergency! Your PC doesn't react to the keyboard or mouse as expected or worse only displays a blue screen with confusing codes. What do you to do now? Throw it away? Ask your a friend who knows about these things? Pay a professional? Not nice alternatives considering that you could solve the problem on your own if you had just learned to backup!
What should you backup?
It depends! If you want to be able to restore your data - that is emails, documents, photos, music, or anything created by you using a program installed on the PC - but not the programs themselves, you should just copy the files to a CD, DVD, or even a usb drive. Then when any data gets lost through an infection or perhaps hard drive failure you are able to restore the files by simply copying them back to your repaired system. Backing up this way means that you would have to have all the cds for your Operating System, PC drivers and programs. It sounds like alot of work and if you have spent hours getting things just the way you like it, it may be. If you don't have lots of programs restoring will only take an hour or two
If you want to backup your entire hard drive including the operating system and programs it will take longer to create the backup, but as a rule is much quicker to restore. You need special backup software which is able to store all necessary files and settings correctly to a backup drive. If your system gets damaged, you can restore your PC to the state it was in at the last backup. How often you do this type of backup depends on how much data you are prepared to lose. Companies usually make "incremental" back up daily and do a full backup once a week. Incremental backups are mini backups - it just backs up files that have changed since the last full backup.
Backups can be stored on disks such as ZIP or usb drives, CD-R or CD-RW, DVDs, tape drives or to a drive on another machine in a network if you have one. The danger with network backs is if one pc gets infected, often it spreads to all the PCs on the network.
Hard disk imaging software is a popular method of backing up. Most imaging software will write the image directly to your cd/dvd writer, a network drive or another hard drive or partition. Restoring from images usually takes less than an hour - a basic system can be completely restored in 15 minutes.
Many companies and some private individuals use data mirror techniques within RAID. Two or more hard drives are operated in such a way that the operating system sees them as one. Each byte of data is stored with a special technique on all available disks so that if one hard disk crashes, the others are not affected and the system continues to run. The faulty drive is then replaced and RAID rebuilds the data on the new disk from the other drives. This backup concept has one big disadvantage: if a PC using mirrored RAID array gets infected, all the drives are infected because the virus is immediately written to all the drives .