The word "restore" means to return something to its former condition. Therefore, when you restore a computer or other electronic device, you return it to a previous state. This may be a previous system backup or the original factory settings.
Restoring a computer, often called a "system restore," is often done as a last resort to fix a problematic machine. For example, if a virus has infected a large number of system files, a system restore may be the only way to get the computer to run smoothly again. If a hard drive has become corrupted and cannot be repaired using a disk utility, it may be necessary to reformat the hard drive and restore the computer from the original operating system installation discs. System restores may also be performed to wipe all data from a computer before selling it or transferring it to another owner.
Since restoring a computer returns it to a previous state, the process also erases any new data that has been added since the previous state. Therefore, you should always back up your data before restoring a computer. The backup should be saved to an external hard drive or another disk other than the one being restored. Once you have restored the computer, you may transfer your files from the backup device back to the computer.
While the term "restore" is often associated with computers, other devices can be restored as well. For example, if a smartphone is repeatedly malfunctioning, it can often be fixed by restoring the system software. Most video game consoles can also be restored by running the restore operation within the system settings. Both iPods and iPhones can be restored using Apple's iTunes software. No matter what device you choose to restore, remember that the process will erase data saved on the device. Therefore, the first step in restoring a computer or any other device should be to back up your personal data.