Complementary Metal Oxide Semiconductor

Complementary Metal Oxide Semiconductor(CMOS) is a small portion of battery powered memory on the motherboard that contains system settings like types of drives, device types in the system, which drive to start up from etc.
The battery used is a 3volt battery.
CMOS and BIOS are often interchanged although they are different things. Think of the BIOS as the skeleton frame upon which the CMOS settings hang.
All computer memory forgets everything it holds when power to it is shut off. If the power was totally shut off to your CMOS, your computer would forget its start up settings, and you’d have to re-enter these settings every time you started your computer! Fortunately this is not the case as your CMOS always receives enough power to remember its settings, even when your computer is off. How? It is powered by a small lithium battery on your motherboard. Lithium batteries are designed to last years, and often outlive the usefulness of the computer they reside in. If you keep a computer long enough, you will have to replace the battery. This is usually an easy task. Just lift the retaining clip, pop out the old battery and put in a new one. Make sure your computer is off though, and beware of static discharge! After you replace the battery, you WILL HAVE TO re-enter all startup settings into CMOS setup.
It is a good idea to enter the CMOS setup and write down the information it contains. Unless you are fairly knowledgeable in computer support, have original manuals or like frustrating experiences, it is a good idea to keep the CMOS information on paper in case it gets erased.
HOW TO GET INTO THE CMOS?
Computers differ on how to enter setup. Normally when you start your computer, it will say something like "Hit or to enter setup. Based on different company or model the cmos entering key also varies " Take note of what key (or combinations of keys to hit. You can safely look around the setup program. If you accidentally change something, just exit without saving
What is CMOS Setup?
Various devices are attached to a computer. These devices have got various parameters such as IRQ settings, DMA channel settings, etc. Thus this information about the devices or peripherals attached to the computer must be known at the time of startup. These parameters are manually set if the devices are of older types that are non-plug-n-play. But if these devices are plug-n-play then the parameters are detected automatically. This information about the devices is to be stored or else it has to be set every time the machine is started. So this information is set and stored in the CMOS setup.
The CMOS has got a jumper. This jumper is used only for clearing the data stored in the CMOS.
Setting up CMOS setup.
The listing below is showing all the information’s stored into the BIOS;
· Time and Date
· Number of Floppy Disk Drives
· Floppy Disk Drives information’s (size, number of track, sectors, head, etc)
· Number of Hard Disk Drives
· Hard Disk Drives information’s (size, number of track, sectors, head, mode, etc)
· Number of CD-ROM Drives
· CD-ROM Drives information’s (operating mode, etc)
· Boot sequence ( Enable the user to decide what disk will be checked first when booting)
· Cache Memory information’s (size, type, timing, etc)
· Main Memory Information’s (size, type, timing, etc)
· ROM Shadowing information’s (Enabling or disabling of Video and System ROM shadow)
· Basic Video mode information’s (EGA, VGA, etc)
· Setting of PCI and ISA slots
· AGP Port Settings (aperture size, etc)
· Virus Protection Warning
· Setting of COM Ports (Enabling or disabling of Com port 2 for instance)
· Password Protection (enable the user to set his password)
· Energy saving information’s (snooze modes for the HDD and monitor)
Depending on your BIOS type there could be many a lot of other information not listed above that can possibly be stored in the BIOS memory. Note that some of the information in the above list may not be a part of the BIOS installed on your computer.

TROUBLESHOOT THE SYSTEM BOARD

In this basic motherboard troubleshooting tutorial, you will learn about system board configurations, ROM BIOS troubleshooting, basic hardware components, physical memory and basic configuration errors and system memory basics. This motherboard configuration and microprocessor troubleshooting tutorial help you identify the basic system board problems. There are many replacable components on a mother or system board such as RAM, ROM, CMOS battery and ROM BIOS. If any of these components functions improperly, you can replace the faulty components with the new components. The Microprocessor and the ROM BIOS are the two major components that are responsible for the problems that are generated for the system board. While proceeding with the troubleshooting, you should from the Microprocessor and the ROM BIOS. There are a large number of the hardware failure symptoms that are associated with the system board. Typical symptoms associated with system board failure are the following.
1. The system locks up during working

2. The system produces a one long beep and 3 short beeps.

3. Current time and time disappear or changed.

4. DMA error message occurs

5. Low CMOS battery message appears.

6. CMOS checksum failure message appears

7. A 201 error message appears which indicates the RAM failure.

8. A Parity check message appears which also indicates the RAM error.

9. The On/Off indicator lights of the system are working, hard drive is also spinning up but there is no boot up starts.

10. The On/Off lights are working and there is also a display on the monitor but the hard disk doesn’t starts up and no system boot ups occur.
Configuration Problems
The configuration problems are most likely to occur when the system starts up for the first time or there is some new installation has been performed on the system. The values and configurations that are stored in the CMOS but accurately reflect the configurations. Incorrectly CMOS values results in the associated hardware to fail. In the advanced CMOS settings, check the enabling functions as a part of the hardware configurations. There are many configuration options in the modern BIOS and a user must have the knowledge of how to configure them. If you can see the startup screen on which BIOS information is displayed, you can consider that there is not basic hardware configuration problems exists in the basic hardware components. After this point, the system starts to load the device drivers and other additional components information and next to this point, the system loads the operating system. If the error occurs after the CMOS display and before the boot up tone, you must clean boot the system.
Microprocessors Troubleshooting
If the Microprocessor fails to work, you must hear a slow beep sound or no display occurs at the monitor screen. This tells that some internal hardware or configuration errors have stopped the microprocessor’s internal circuitry to work. Some kinds of internal problems allow microprocessor to work but in case of extra working, microprocessor fails to perform additional work. The best solution for the microprocessor’s problems is to replace it with a new one. If the system locks up for a continuous few minutes, this means that the fan of the microprocessor or the internal cooling mechanism is not working properly. In this scenario, you should replace the fan of the microprocessor to provide it continuous cooling.
RAM Errors
RAM is a serviceable part of the system board and the RAM failure basically can be categorized into the following two categories. Soft-memory errors: Soft memory errors are the errors that are caused by the infrequent glitches in the operation of the system. These errors can be controlled just by restarting the system. Hard-memory errors: Hard memory errors are the permanent physical errors and that requires that memory units should be checked properly and replaced.
ROM BIOS Setup Erros
A malfunctioning or damaged ROM stops the systems’ working completely. If the system board is dead, you should first examine the BIOS chip for any kind of physical damage. If the BIOS chip is heated up, it is most likely for it to crack. Another symptom that points towards the damaged RAM is bootup sequence automatically moves into the CMOS configuration display. In this situation, you must replace the faulty BIOS chip with another one, which matches according to your system’s configurations. Another cause of the system’s failure or problem is the malfunctioning of the CMOS battery. If the system fails to display the current time and date, the most likely reason for this is the faulty CMOS battery and the only solution for this is to replace the battery with the new one. In case the battery is replaced, the configurations and settings in the CMOS chip are lost, the only method for the configuration is to access the CMOS batter and reconfigure the system.