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Figure 7-32 A CMOS battery

If the battery runs out of charge, you lose all of your CMOS information. If some mishap suddenly erases the information on the CMOS chip, the computer might not boot up or you’ll get nasty-looking errors at boot. Any PC made after 2002 will boot to factory defaults if the CMOS clears, so the chances of not booting are slim—but you’ll still get errors at boot. Here are a few examples of errors that point to lost CMOS information:

CMOS configuration mismatch

CMOS date/time not set

No boot device available

CMOS battery state low

Here are some of the more common reasons for losing CMOS data:

Pulling and inserting cards

Touching the motherboard

Dropping something on the motherboard

Dirt on the motherboard

Faulty power supplies

Electrical surges

Chip creep

Most of these items should be fairly self-explanatory, but chip creep might be a new term for some of you. As PCs run, the components inside get warm. When a PC is turned off, the components cool off. This cycling of hot and cold causes the chips to expand and contract in their mounts. Although the chip designers account for this, in some extreme cases this thermal expansion and contraction causes a chip to work out of its mount and causes a failure called chip creep. Chip creep was a common problem in the earlier days of PCs, but after more than a quarter century of experience, the PC industry has done a pretty good job of designing mounts that hold all of your chips in place dependably.

If you encounter any of these errors, or if the clock in Windows resets itself to January 1st every time you reboot the system, the battery on the motherboard is losing its charge and needs to be replaced. To replace the battery, use a screwdriver to pry the battery’s catch gently back. The battery should pop up for easy removal. Before you install the new battery, double-check that it has the same voltage and amperage as the old battery. To retain your CMOS settings while replacing the battery, simply leave your PC plugged into an AC outlet. The 5-volt soft power on all modern motherboards provides enough electricity to keep the CMOS charged and the data secure. Of course, I know you’re going to be extremely careful about ESD while prying up the battery from a live system!

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NOTE All techs invariably do things in CMOS they want to undo, but sometimes simply making a change in CMOS prevents you from getting back to the CMOS setup utility to undo the change. A great example is when someone sets a CMOS password and then forgets the password. If you ever run into a system with an unknown CMOS password, you’ll need to erase the CMOS and then reset everything. You’ll recall from Chapter 5, “Microprocessors,” that all motherboards have a clear CMOS jumper. Refer back to that chapter for the steps on resetting CMOS.

Flashing ROM

Flash ROM chips can be reprogrammed to update their contents. With flash ROM, when you need to update your system BIOS to add support for a new technology, you can simply run a small command-line program, combined with an update file, and voilà, you have a new, updated BIOS! Different BIOS makers use slightly different processes for flashing the BIOS, but in general you must boot from a floppy diskette and then run the relevant updating command from the A:\> prompt. This example shows how simple it can be:

A:\> aw athxpt2.bin

Some motherboard makers provide Windows-based flash ROM update utilities that check the Internet for updates and download them for you to install (Figure 7-33). Most of these utilities also enable you to back up your current BIOS so you can return to it if the updated version causes trouble. Without a good backup, you could end up throwing away your motherboard if a flash BIOS update goes wrong, so you should always make one. Other motherboards have drivers to read flash ROM-based USB drives and have a flashing utility built in to ROM. You can download an update, put it on a thumb drive, and boot to the CMOS setup utility to