System clock loses time

Helpline Q&A Directory

My HP computer is switched on all the time as I use it to receive fax messages and take voicemail. However, I notice that the clock in the bottom righthand corner loses about 10 minutes a day. What's happening, and how can I correct it?

This is a common question. There are two clocks inside your computer. First, there's the battery-powered clock that keeps time when the PC is switched off. This is the most accurate clock in the computer, but it isn't uncommon for it to lose or gain up to a few seconds a day.

There is also the clock maintained by Windows 95/98/Me, which displays the time in the Taskbar. This clock is set from the battery-powered clock only at startup, or whenever the PC is woken up after going into standby. During normal use, it is updated by Windows itself. It is updated using a timer interrupt generated by the computer motherboard. Motherboard timing signals are not designed to be highly accurate, and they can even be ignored if the computer is very busy, so a significant drift may occur.

If you are wondering why Windows doesn't use the more accurate clock, the reason is because of the Windows 95 family's DOS heritage. DOS was designed to run on computers that didn't have a built-in clock, so it had to be able to keep time for itself.

Windows 95 and its descendants were designed to be as compatible as possible with DOS. Windows NT and Windows 2000 don't have this restriction; they regularly update their clocks from the battery-powered system clock, so you shouldn't experience any serious time inaccuracy if you use those operating systems.

So much for the explanation: what about the solution? Well, you could buy a radio-controlled clock that receives accurate time signals from station MSF, and pass this information to the computer through a serial port. You could also buy software and interface cables that allow the clock to be updated using a GPS (global positioning system) receiver. However, we suspect that you don't need that level of accuracy, and you will almost certainly find those solutions too expensive.

You probably use your PC to connect to the internet several times a day. The cheapest solution would therefore be to install some shareware that checks to see when you are connected to the web and then updates the clock from an internet time standard. There's a great variety of programs to choose from, including SocketWatch (www.locutuscodeware.com/swatch.htm) and (www.hiclock.com). Another example is Get Global Time, a free downloadable utility available from www.get-time.org.