Why Do Desktop Computers Need Batteries?
Every computer, whether desktop or laptop, has a small battery on the motherboard. In the early days of computing, this battery was essential for the operation of a computer. As time has gone on, computer manufacturers have found a way to get around using the battery for every function except one.
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BIOS
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All computers have a basic input-output system, or BIOS, that is a piece of software that allows the operating system and software to interact with the computer hardware, such as the hard drive or the memory. The basics of a computer BIOS are stored on a ROM chip, meaning that they cannot be changed and require no power to be maintained. Any customizations that the user makes, however, cannot be stored on the ROM, so they are stored in the CMOS.
CMOS
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Computer batteries are often called CMOS batteries. CMOS stands for complementary metal-oxide semiconductor, which was the technology that was originally used in the circuitry that the battery powered. The CMOS is a piece of low-power memory (meaning it only takes a small amount of electricity to keep it running) that holds all of the system setup parameters. Because the CMOS is a piece of random access memory (RAM), it can be modified so that the user can change the BIOS settings, but it also means that it needs constant power in order to store these settings. A battery was required to keep the CMOS running while the computer was off.
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Function
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By 2010, computer manufacturers had stopped using RAM as a method for holding the BIOS settings in favor of dedicated flash memory, which requires no power to remember the settings. This left the computer battery with only one task to do, power the internal clock. There is no way to have the computer know the current date or time without the clock constantly running. For modern computers, the internal battery is little more than a watch battery.
Battery Type
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The internal computer battery is a disk shape and stored on the motherboard. Most manufacturers will not list the exact model of CMOS battery. To get this information, in case you need to replace it, you have to open the computer and find the battery on the motherboard. The battery information, such as voltage, chemistry and packaging, will be printed on the top of the battery. Use this information to purchase a replacement.
Bad Battery Symptoms
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On older systems, when the CMOS battery goes bad, the computer may start to lose its BIOS settings, such as which drive to boot from or how much RAM to access. These computers may also display errors with the word "CMOS" in them, which is normally a sign of a bad CMOS battery. On any computer, new or old, if the computer shows a very old date and time after booting up, or if the computer clock is constantly slow, the CMOS battery is to blame.
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References
- Photo Credit motherboard image by jovica antoski from Fotolia.com
