How to Update a CMOS


Updating your CMOS should ideally only be performed if you have a need to do so. Updating is required, for example, if you install a new hard drive that is not supported by the old version of your computer's CMOS. This CMOS update was traditionally done using a 3.5 inch floppy drive. However, most computers nowadays don't have a floppy drive, so the best method of updating your CMOS involves the use of a bootable CD or USB flash drive. If you prefer, you can still update your CMOS using a floppy drive as long as your computer is equipped with one.

Things You'll Need

  • BIOS update and program files from CMOS manufacturer's website
  • Ultimate BIOS Boot Edition utility all-in-one
  • CD burning program such as Nero that supports burning bootable CDs
  • UltraISO Trial version
  • Blank CD-R or CD-RW
  • CD burner drive

Creating the bootable CMOS update CD

  • Download and install UltraISO or any program that will open ISO files (see Resources).

  • Open "" and extract the "drdosmin.img" file to the desktop by dragging and dropping it.

  • Open the "drdosmin.img" file in UltraISO by clicking "File" then "Open" and selecting the file on the desktop.

  • Download the BIOS update file and DOS update program from your CMOS manufacturer's website. In UltraISO, browse to the folder where you saved these two files in the file browser window at the bottom of the program window. Drag and drop these two files into the main window with the other three files, "," "" and "" These files are the bootable files.

  • Click "File" and select "Save as" to save all this data to a new image file which you'll use with your CD burning program. Save the modified image file as "drdos.img" and close UltraISO.

  • Start Nero or your preferred CD burning application, and create a "new compilation" with the CD-format "CD-ROM - Bootable." Open the Menu option and click the "Boot" tab. Click the "Image file" option and use the "Browse" button to browse for the hard drive location where you saved the "drdos.img" file. Click the "New" button to create the compilation.

  • Click the "Burn" button in the program's main interface to begin burning your bootable CMOS update CD.

Updating the CMOS

  • Press "Del" or whatever key is required to enter the BIOS setup when the computer is booting at the info screen. Here, check your boot order to put the CD-ROM first, so that you can boot from your CD.

  • Insert your CD and restart the computer. If all goes as planned, you'll see a DOS-Prompt (A:>).

  • Access the flash update program by typing its filename and extension at the DOS prompt. Use the flash program to flash your computer's CMOS.

Tips & Warnings

  • If you encounter any problems during the flashing process, don't turn off the PC and don't panic. Access the web on another computer and search the web for solutions to fix the problem.

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  • Photo Credit bios chip image by Nikolay Okhitin from
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