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My problem

If my PC is turned off for an extended period of time (not restarted, or turned back on within 30 or so seconds of a full shutdown) Then my PC will boot to the initial ASUS bios screen which will prompt me to press F1 to enter BIOS configuration, from there I press ESC and don't save - I can then boot to my OS without issue.

For months I have become quite adept at pressing F1, Esc and then Enter quickly to boot in to my OS.

Key things to point out

  • As I mentioned previously, this will only happen after my PC is turned off for some time. If I reboot or power down and back on quickly my OS will load straight away.
  • My PC time is always wrong by a lot of hours, (my timezone is correct). Even if I change it, next time I turn it back on after 12-16 hours of downtime it will be completely wrong (I suspect this is my CMOS battery)?
  • This is the first PC I built myself from scratch, although I have no other issues and this is only a 2 second delay to my boot time, it is quite annoying.

My Thoughts

I think the CMOS battery is causing the internal clock issues, but does that also effect my BIOS settings/memory in some way? It's almost like my BIOS is loading in to first time configuration setup, so it's like it's forgetting it's config? Does my CMOS power some sort of BIOS setting held in memory?

DavidPostill
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Samuel Nicholson
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1 Answers1

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Does my CMOS power some sort of BIOS setting held in memory?

Yes, this is very common, especially in older PCs

The choices you make in the "BIOS" screens are saved in non-volatile RAM and power from the "CMOS battery" is used to preserve that information. The settings might include something fundamental like the fact you want the boot-order to always ignore the CD for security reasons. The motherboard firmware knows if settings have never been made (or have been lost due to battery failure) and therefore directs you into the BIOS screens.

As you surmise, timekeeping relies on the "CMOS battery" providing a tiny amount of power to an on-board clock. At least until the operating system can contact a time-server through a network connection.

Either your "CMOS battery" is dead, wrongly inserted or there is a fault on the motherboard.

Terms like CMOS and BIOS are a bit antiquated and shouldn't be taken literally (they have rather narrow specific meanings)

See also

Community
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RedGrittyBrick
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