With all the progress and improvements that have been made with computer hardware, why are some things like the CMOS battery still necessary? Today’s SuperUser Q&A post has the answer to a curious reader’s question.
Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.
Photo courtesy of Jim Bauer (Flickr).
The Question
SuperUser reader Joseph Philipson wants to know why PCs still require a CMOS battery:
Why do PCs still require a CMOS battery?
The Answer
SuperUser contributors nhinkle and smokes2345 have the answer for us. First up, nhinkle:
Followed by the answer from smokes2345:
The primary function of this is to keep the clock running even when the computer is turned off. Without the CMOS battery, you would need to reset the clock every time you turned on the computer.
On older systems the CMOS battery also provided the small amount of charge required to maintain the non-volatile BIOS memory, which remembered BIOS settings between reboots. On modern systems this information is typically stored in flash memory and does not require a charge to be maintained.
Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.
However, with modern computers the CMOS battery plays a lesser role as most BIOS firmware is smart enough to automatically detect the correct settings and those settings are stored such that they do not need power to persist. The CMOS battery is still required to maintain the RTC though.
More information is available at the following Wikipedia page: Nonvolatile BIOS Memory (CMOS Battery)
