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Clearing CMOS

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  • Motherboards
  • BIOS
  • CMOS
Last response: in Motherboards
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September 9, 2012 12:31:41 AM

Hi. I had a question on clearing the cmos, but before anyone jump to conclusion saying this is something I should look up before asking, I've tried to look for the answer online but with no luck or I haven't looked hard enough. Say that my bios has a certain version say version X. When I clear my cmos, does my bios version downgrade or just stay at version X. Thanks!

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a b V Motherboard
September 9, 2012 1:00:15 AM

stays at that version. It just clears any changes you made and sets it back to the default settings.
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a c 178 V Motherboard
September 9, 2012 1:12:21 AM

mrantec300 said:
Hi. I had a question on clearing the cmos, but before anyone jump to conclusion saying this is something I should look up before asking, I've tried to look for the answer online but with no luck or I haven't looked hard enough. Say that my bios has a certain version say version X. When I clear my cmos, does my bios version downgrade or just stay at version X. Thanks!


The firmware itself is usually stored on an 8megabit (1MiB) EEPROM, it's not volatile and persists even when there's no power. Due to the nature of EEPROM chips it's not advisable to write to them unless absolutely necessary, so firmware settings are typically stored on a small SRAM chip which is volatile, meaning that if it loses power the stored data will be lost. This is why pulling the clock battery or decoupling it via a jumper will zero out the SRAM chip and subsequently force the firmware settings to reset to defaults.

Newer motherboards store the firmware on 64megabit Flash chips rather than EEPROM. Flash is an evolution of EEPROM which is structurally similar but advanced enough that the settings can be stored on the same chip. Since Flash is non-volatile, pulling the battery is not enough to reset the settings, normally a jumper or push button must be used.

If your motherboard has an EFI firmware it almost certainly stores everything in Flash. Motherboards that have Hybrid BIOS/EFI firmware will use Flash as well, BIOS still typically runs on EEPROM but will occasionally be on Flash.

So, read your motherboard manual to figure out how to properly reset the settings before doing so.
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September 9, 2012 2:37:04 AM

Best answer selected by mrantec300.
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