Explain Clearing Cmos Settings - Tom's Hardware Forum

Home » What Does Clearing Cmos Do » Explain Clearing Cmos Settings - Tom's Hardware Forum

Maybe your like

Tom's Hardware Forum

Search

Everywhere Threads This forum This thread Search titles only Note By: Search Advanced search… Everywhere Threads This forum This thread Search titles only By: Search Advanced… Log in Register What's new

Search

Everywhere Threads This forum This thread Search titles only Note By: Search Advanced search… Everywhere Threads This forum This thread Search titles only By: Search Advanced… Toggle sidebar Toggle sidebar Menu Install the app Install How to install the app on iOS

Follow along with the video below to see how to install our site as a web app on your home screen.

Note: This feature may not be available in some browsers.

  • Home
  • Featured
  • Forums New posts Search forums
  • What's new Featured content New posts Latest activity
Explain clearing cmos settings
  • Thread starter Thread starter marv100
  • Start date Start date Jun 18, 2011
  • Tags Tags CPUs
Toggle sidebar Toggle sidebar
  • Home
  • Forums
  • Hardware
  • Motherboards
You are using an out of date browser. It may not display this or other websites correctly.You should upgrade or use an alternative browser. Status Not open for further replies. M

marv100

Distinguished
Jun 17, 2011 3 0 18,510 Hello, does clearing bios bring back original bios, in case flashing caused a bricked motherboard? Sort by date Sort by votes pjmelect

pjmelect

Splendid
Jul 14, 2006 3,225 31 21,440 The CMOS memory is where the BIOS stores its settings. Clearing the CMOS memory sets all the CMOS memory locations to FFH this is detected by the BIOS which then loads its default values. Clearing the CMOS does not affect the BIOS program in any way. You should always clear the CMOS after you upgrade the BIOS as the updated BIOS can use different memory locations in the CMOS memory and the different (wrong) data can cause unpredictable operation or even no operation at all. Upvote 0 Downvote Motopsychojdn

Motopsychojdn

Illustrious
Jan 26, 2010 11,746 3 41,960 If you have 'bricked' your motherboard maybe because a biosflash was interrupted for example, then you need to either replace your bios chip or find a bookshelf with a motherboard-sized space on it Moto Upvote 0 Downvote C

compulsivebuilder

Distinguished
Jun 10, 2011 578 1 19,160 Not quite so fast, moto! Quite a few motherboards these days have two BIOS chips, and you can only flash the first one. If you have a failure during the flashing process, then you can boot from the second BIOS (the manual will tell you how to do that) and then repeat the flashing process with a good BIOS. As for your direct question, pjmelect has it right - the clearing process only clears the small amount of CMOS memory which holds the parameters which control what the BIOS does (like what settings to use for RAM, which drive to boot from, etc). It won't fix your BIOS - sorry! Upvote 0 Downvote Motopsychojdn

Motopsychojdn

Illustrious
Jan 26, 2010 11,746 3 41,960 ^Live and learn hehe, I've not encountered any 2 chip boards yet though Moto Upvote 0 Downvote M

marv100

Distinguished
Jun 17, 2011 3 0 18,510 pjmelect : The CMOS memory is where the BIOS stores its settings. Clearing the CMOS memory sets all the CMOS memory locations to FFH this is detected by the BIOS which then loads its default values. Clearing the CMOS does not affect the BIOS program in any way. You should always clear the CMOS after you upgrade the BIOS as the updated BIOS can use different memory locations in the CMOS memory and the different (wrong) data can cause unpredictable operation or even no operation at all. Thank you for that involved explanation. What is FFH? Your explanation is extremely important to me, but I don't understand it yet. Does flashing replace original BIOS program or put a new program in another area of cmos memory or something else? Will clearing cmos settings enable bootup to use original cnmos/bios settings? If so, why would one clear cmos/bios if flashing worked? one person told me flashing produces a set of cmos/bios settings in a different memory area than the original (enabling bootup to use new bios/cmos settings) and clearing cmos enables bios to return to original cmos settings useable on bootup. Is that true? Marv100 Upvote 0 Downvote pjmelect

pjmelect

Splendid
Jul 14, 2006 3,225 31 21,440 Flashing a new BIOS erases and overwrites the original BIOS which is stored in the BIOS flash memory. This is not the same as the CMOS memory which is battery backed. When the CMOS memory is cleared all of the memory locations are set to a logic “one” and as the CMOS memory is eight bits wide this is 255 decimal or to a programmer FFH. When you flash a new BIOS it may use different memory locations in the CMOS memory to the old version which can cause unpredictable operation or even no operation at all. Clearing the CMOS memory causes the BIOS program to set all of its settings to its default values. Upvote 0 Downvote M

mikrev007

Distinguished
Oct 28, 2008 264 0 18,790 CMOS is not even a part of the BIOS-chip. It is located elsewhere. Upvote 0 Downvote M

marv100

Distinguished
Jun 17, 2011 3 0 18,510 pjmelect : Flashing a new BIOS erases and overwrites the original BIOS which is stored in the BIOS flash memory. This is not the same as the CMOS memory which is battery backed. When the CMOS memory is cleared all of the memory locations are set to a logic “one” and as the CMOS memory is eight bits wide this is 255 decimal or to a programmer FFH. When you flash a new BIOS it may use different memory locations in the CMOS memory to the old version which can cause unpredictable operation or even no operation at all. Clearing the CMOS memory causes the BIOS program to set all of its settings to its default values. Thank you very much, this seems to be much clearer to me. As I understand your explanation flashing not only overwrites BIOS memory, but also may write to cmos. If the writing to cmos changes the value of those 256 bits, screwup may occur. In addition, clearing the cmos will nullify any writing flashing did to the cmos because it will all be set to logic one, and change bios back to default, (original settings), as they were before flashing. Did I understand correctly? Thanks again for all that patience. Marv100 Upvote 0 Downvote pjmelect

pjmelect

Splendid
Jul 14, 2006 3,225 31 21,440 Flashing the BIOS does NOT write to the CMOS memory which is on a totally different chip. The BIOS uses the CMOS memory to store its configuration data. The CMOS memory is eight bits wide and depending on the manufacturer can be 64 bytes or more long. Upvote 0 Downvote Status Not open for further replies. Share: Facebook X Bluesky LinkedIn Reddit Tumblr WhatsApp Email Share Link

TRENDING THREADS

  • amdfangirl DiscussionWhat's your favourite video game you've been playing?
    • Started by amdfangirl
    • Aug 3, 2014
    • Replies: 4K
    PC Gaming
  • Admin NewsPirate archivist group scrapes Spotify's 300TB library, posts free torrents for downloading — investigation underway as music and metadata hit torr...
    • Started by Admin
    • Today at 10:06 AM
    • Replies: 18
    News Comments
  • Admin NewsRegistry hack enables new performance-boosting native NVMe support on Windows 11 — Windows Server 2025 feature can be unlocked for consumer PCs, bu...
    • Started by Admin
    • Saturday at 9:16 AM
    • Replies: 66
    News Comments
  • T QuestionCable test sort of?
    • Started by tml812
    • Today at 1:40 PM
    • Replies: 8
    Networking
  • Blackapino QuestionWhich Prebuild Do I get a Co-Worker for Gaming
    • Started by Blackapino
    • Today at 3:16 PM
    • Replies: 7
    Prebuilt & Enterprise
  • P QuestionIs this 2x16gb in dual channel? (CPU-Z capture)
    • Started by psaez84
    • Today at 4:43 PM
    • Replies: 3
    Memory
  • NoPuhi QuestionOn the fence: Maximus IX Hero
    • Started by NoPuhi
    • Today at 1:39 PM
    • Replies: 7
    Motherboards

Latest posts

  • davidson1 QuestionArctic freezer pro 3 360 rgb runs constantly at 3000 rpm
    • Latest: davidson1
    • 13 minutes ago
    Cooling
  • S QuestionMotherboard suddenly dead?
    • Latest: sshapeshiftt
    • Today at 10:50 PM
    Systems
  • thestryker QuestionConcerns about my CPU temps ?
    • Latest: thestryker
    • Today at 10:42 PM
    Cooling
  • donjohnn QuestionUpgrading 8 year old Pre-built
    • Latest: donjohnn
    • Today at 9:55 PM
    Prebuilt & Enterprise
  • S QuestionPSU fan not spinning and nothing seemingly gets power when turning on psu switch, but keyboard lights up?
    • Latest: seattlepurple
    • Today at 9:42 PM
    Systems
  • S QuestionTrying to decide on whether or not to pull the trigger on this z790 build.
    • Latest: Supra-User
    • Today at 9:21 PM
    Systems
  • Aeacus QuestionPSU making system freeze.?
    • Latest: Aeacus
    • Today at 9:21 PM
    Systems

Moderators online

  • kanewolf

Share this page

Facebook X Bluesky LinkedIn Reddit Tumblr WhatsApp Email Share Link COMPANY Space.com is part of Future plc, an international media group and leading digital publisher. Visit our corporate site. © Future Publishing Limited Quay House, The Ambury, Bath BA1 1UA. All rights reserved. England and Wales company registration number 2008885. RESOURCES
  • Advertising
  • Cookies Policies
  • Privacy
  • Term & Conditions
  • Topics
FOLLOW Facebook Twitter Instagram Top Bottom

Tag » What Does Clearing Cmos Do