# Which chip is a motherboard battery powering?

**URL:** <https://boards.straightdope.com/t/which-chip-is-a-motherboard-battery-powering/676907>\
**Category:** Factual Questions\
**Created:** [December 21, 2013, 5:22pm UTC](https://boards.straightdope.com/t/which-chip-is-a-motherboard-battery-powering/676907 "2013-12-21T17:22:44Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\
**Post date:** [December 21, 2013, 5:22pm UTC](https://boards.straightdope.com/t/which-chip-is-a-motherboard-battery-powering/676907/1 "2013-12-21T17:22:44Z")

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I know that the battery is not powering the BIOS chip. The BIOS itself is non-volatile and doesn’t require any power to retain data.

Therefore it must be some other chip that is powered from that CR20xx cell.

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**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\
**Post date:** [December 21, 2013, 5:30pm UTC](https://boards.straightdope.com/t/which-chip-is-a-motherboard-battery-powering/676907/2 "2013-12-21T17:30:10Z")

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[CMOS RAM.](http://en.wikipedia.org/wiki/Nonvolatile_BIOS_memory)

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**Author:** ![StrangerThanFiction](https://avatars.discourse-cdn.com/v4/letter/s/f05b48/32.png) [@StrangerThanFiction](https://boards.straightdope.com/u/StrangerThanFiction)\
**Post date:** [December 21, 2013, 5:34pm UTC](https://boards.straightdope.com/t/which-chip-is-a-motherboard-battery-powering/676907/3 "2013-12-21T17:34:54Z")

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My understanding is that it powers the CMOS RAM, which retains the current date and time as well as any user-configured BIOS settings. Motherboards I’ve played around with have 640k of standalone CMOS RAM, but I think some have that memory wrapped up into another component (memory controller?).

Edit: BAH!

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**Author:** ![panamajack](https://avatars.discourse-cdn.com/v4/letter/p/47e85d/32.png) [@panamajack](https://boards.straightdope.com/u/panamajack)\
**Post date:** [December 21, 2013, 5:37pm UTC](https://boards.straightdope.com/t/which-chip-is-a-motherboard-battery-powering/676907/4 "2013-12-21T17:37:10Z")

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It’s for the RTC (real-time clock).

The OP already covered the memory. Battery-backed CMOS isn’t used anymore.

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**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\
**Post date:** [December 21, 2013, 6:00pm UTC](https://boards.straightdope.com/t/which-chip-is-a-motherboard-battery-powering/676907/5 "2013-12-21T18:00:40Z")

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> [@beowulff](#):
>
> [CMOS RAM.](http://en.wikipedia.org/wiki/Nonvolatile_BIOS_memory)

Thanks!

From that link:

> [@](#):
>
> The CMOS RAM and the real-time clock have been integrated as a part of the southbridge chipset and it may not be a standalone chip on modern motherboards.

So the battery powers the southbridge.

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**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\
**Post date:** [December 22, 2013, 11:23pm UTC](https://boards.straightdope.com/t/which-chip-is-a-motherboard-battery-powering/676907/6 "2013-12-22T23:23:12Z")

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> [@Dog80](#):
>
> So the battery powers the southbridge.

The battery powers a tiny part of that chip when the main power is off.