Problems Solved

PROBLEM OF THE FORTNIGHT

What happens when I remove my PC’s CMOS battery?

Q Your reply to Jim Fraser in Issue 619’s Problems Solved (page 67) made me wonder what will happen to my computer’s settings when the time comes to replace the CMOS battery. Assuming I need to shut down the PC and unplug it from the mains, will I lose everything when I remove the battery? My PC is approaching six years old, so I feel it’s time to replace the battery. Keep up the great magazine.

Keith Holman

A This is a great question, because it takes into consideration aspects that many might take for granted.

So first, yes – it’s extremely wise to unplug a PC from the mains before performing any internal maintenance. You should also discharge any static electricity you may be carrying by touching an earthed metal object or, better still, wearing an earthed, anti-static wrist strap like the pictured example (around £6, www.snipca.com/40450). Plenty of people – us included – have tinkered inside a PC without bothering to take this precaution and have got away with it, but we wouldn’t advise this.

With that clear, replacing the battery is usually a quick, simple job that poses no threat whatsoever to the data on your computer’s storage drives. That means Windows and all your apps are safe, as are your personal files and folders.

One thing you might lose, however, is the data stored in your PC’s BIOS or UEFI, because that’s what the CMOS battery keeps alive. It includes things like your PC’s digital clock, and the order in which the computer looks for a drive from which to boot Windows.

For many users, the only BIOS/UEFI settings that have changed from the defaults are the time and date, in which case there’s no need to worry about losing them. What’s more, if you’re quick when changing the battery, there’s often enough residual capacitance in