Complementary Metal Oxide Semiconductor (CMOS)

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A Complementary Metal Oxide Semiconductor (CMOS) is a battery-backed bank of flash memory chips on the motherboard. The information and settings stored in CMOS can be flashed, meaning that they can be changed. The information stored in the CMOS is read by the system basic input/output service on startup. A lithium battery on the motherboard provides power to hold the CMOS system settings when the computer is off. If the CMOS battery begins to lose some of its battery charge, a CMOS checksum error may appear when the computer starts up. If the battery loses its charge completely, chances are some or all of your system settings will be lost, including date and time, hard drive settings, and system password.

Knowing that the system settings will be lost if the CMOS battery loses its charge or is removed from the motherboard can prove useful. If you don't know the password to enter the system setup, you can remove the CMOS battery, wait about three minutes, and then put the battery back into the motherboard. This process clears the system settings, including the setup password that is locking you out. After clearing the CMOS settings and re-entering setup, you should first check to see if the system date and time are correct. Second, check the major hard drive settings for accuracy, including heads, sectors, and cylinders. Another way to clear the system settings is to short out the CMOS jumper on the motherboard. In other words, locate the CMOS jumper on the motherboard and close, or ‘short' the circuit with a plastic jumper. Consult the motherboard manufacturer's instructions for the location of the CMOS jumper and instructions for this process.

You can modify your system settings by selecting F2 or Delete during system booting. Depending on what type of BIOS is installed on your computer, here are some settings that you can change in the system setup: system setup password, system date and time, boot sequence, parallel port settings, com/serial ports, hard drive type and size, memory, floppy drive, and plug-and-play options.

If the user plans to upgrade the CPU chip, the CMOS chip may have to be changed or upgraded as well. In addition, if a CMOS checksum error ever appears during the system startup, the BIOS may need upgrading.



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A+ Complete Study Guide, Third Edition (220-301 and 220-302)
The A+ Exams Guide: (Exam 220-301), (Exam 220-302) (TestTakers Guides)
ISBN: 1584503076
EAN: 2147483647
Year: 2003
Pages: 237

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