[Alug]Bios system time

I have a small problem with my home machine. The Bios time does not seem to be getting updated with the system time. If I set the time correctly all is fine until I reboot at which point the system time reverts to whatever the bios says it is. Naturally I could go into the bios and reset the time manually but I am interested to find out why it's not getting set by the OS. Does anyone know how the Bios time is updated as the date -s command only seems to affect the system time. Regards Wayne