PC Users Bible

As a last-resort method for restoring your computer's CMOS to a configuration that allows the computer to start, most motherboards include a way to clear the CMOS memory and reset the system to the original default settings.

As explained earlier in this chapter, a small battery keeps the data in the CMOS memory alive by providing a constant charge to the CMOS chip. If the CMOS loses that trickle charge, the RAM on the CMOS shuts down.

The design of the motherboard takes advantage of this by including a jumper (a removable wire or plug) in the signal path that connects the battery to the CMOS RAM chip. When you remove this jumper, you open the circuit, and the CMOS chip loses its trickle charge, which clears the CMOS settings. When you replace the jumper, the battery restores power to the CMOS chip. The next time you turn on the computer, the BIOS sets the CMOS to the default values.

Some motherboards don't have a Clear CMOS Memory jumper, so the only way to clear the CMOS is to physically remove the battery from its socket in the motherboard.

To clear the CMOS memory, follow these steps:

  1. Turn off the computer.

  2. Disconnect the power cable from the back of the computer's case. If you're working on a laptop computer, disconnect the external power supply and remove the battery pack.

  3. Remove the jumper or the battery.

  4. Wait at least ten seconds.

  5. Replace the jumper or the battery. Make sure the battery is right side up.

  6. Plug the power cable back into the computer. If it's a laptop, replace the battery pack.

  7. Turn on the computer. Let it load Windows, just to confirm that it is working properly.

  8. Double-click the time in the lower right corner of the screen to open the Date and Time Properties window.

  9. Set the date and approximate time in the Date & Time tab.

  10. If the computer is connected to the Internet, open the Internet Time tab. Click Update Now to set the exact time.

  11. If you want to change any of the other BIOS settings, restart the computer and open the BIOS Utility.

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