Wednesday, June 11, 2008


All current computers have a chip in them that combines a real-time clock with some nonvolatile RAM memory. This chip is often referred to as the CMOS or CMOS RAM chip and is designed to run off a battery for several years.

The clock enables software to read the date and time and preserves the date and time data even when the system is powered off or unplugged.

The other portion of the chip stores basic system configuration information which is read every time the computer is powered on. The battery preserves the information and powers the clock.

Symptoms that indicate that the battery is about to fail include having to reset the clock on your PC every time you reboot the system and problems during the system’s boot, such as drive-detection difficulties. If you experience problems such as these, you should make note of your system’s CMOS settings and replace the battery as soon as possible.

When you replace a battery, in most cases the existing data stored remains intact for several minutes so purchase the battery in advance and make the battery swap quickly.

When you replace a PC battery, be sure you get the polarity correct; otherwise, you may damage the CMOS chip.

After replacing a battery, power up the system and use the Setup program to check the date and time setting and any other data that was stored in the NVRAM.

Most systems have the setup program built right into the ROM BIOS software. These built-in setup programs are activated by a key sequence usually entered during boot-up. The key is generally shown on the screen during the beginning phase of the boot-up sequence and indicates which key to press to enter the BIOS Setup.
Most likely one of the following keystrokes will be used to enter the BIOS Setup:
Del , F2, Ctrl+Alt+Esc, F1, Ctrl+Alt+S. F10

It is a good idea to record your BIOS settings in advance for future reference.

—In the BIOS Setup main screen, you’ll usually find a main menu allowing access to other menus and submenus offering various sections or screens and instructions as to navigating thru the BIOS screens.
—Record all the settings.
—The setup program has several pages of information, so record the information on each page.
—Most systems do return to the default BIOS settings if the CMOS battery is removed, but you may lose any customized settings.