Why do PCs Still Require a CMOS Battery Even Though They Run on Electricity?

Why do PCs Still Require a CMOS Battery

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 websites.

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The Question

SuperUser reader Joseph Philipson needs to understand why PCs still need a CMOS battery:

Why do computers still need a CMOS battery although they run on electricity? we have a tendency to square measure providing millions of power to the PC by change the central processor plug to our electric board, thus why will it still need a CMOS battery?

Why do PCs still need a CMOS battery?

The Answer

SuperUser contributors Hinkle and smokes2345 have the solution for the North American nation. First up, shingle:

The CMOS battery isn't there to produce power to the PC once it's operational, it's there to take care of any low quantity of power to the CMOS once the PC is battery-powered off and unplugged.

The primary perform of this is often to stay the clock running even once the PC is turned off. while not the CMOS battery, you'd reset the clock on every occasion you turned on the PC.

On older systems, the CMOS battery additionally provided the tiny quantity of charge needed to take care of the nonvolatile BIOS memory, that remembered BIOS settings between reboots. On trendy systems, this info is usually held on in non-volatile storage and doesn't need a charge to be maintained.

Followed by the solution from smokes2345:

Think of it like your lead-acid accumulator. once you undo the battery, your radio looses all of its presets and also the clock resets. Originally, the CMOS battery command an identical perform, maintaining the memory that command the BIOS settings and keeping the time period Clock running.

However, with trendy computers the CMOS battery plays a lesser role as most BIOS code is wise enough to mechanically find the right settings and people settings area unit hold on specified they are doing not want power to persist. The CMOS battery continues to be needed to take care of the RTC although.