Help in better understanding BIOS

Discussion in 'BIOS Mods' started by DonJohn, Mar 22, 2012.

  1. DonJohn

    DonJohn MDL Junior Member

    Jan 16, 2010
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    After I bricked a brand new motherboard in flashing a modded BIOS obtained in this forum I'm trying to better understand BIOS (I keep a tiny hope that I can recover my motherboard!)

    As far as I understand a BIOS file contains 2 main blocks:
    1. boot sector block
    2. main BIOS code block (a main BIOS image)

    The boot sector block contains critical BIOS codes, including memory detection and recovery codes for you to flash a new BIOS image if the original BIOS image is corrupted. When the system powers on, the boot sector
    code executes first. Once it is completed, the main BIOS code will continue with system initialization and bootup.

    These days, the BIOS resides in a SPI Flash EEPROM chip soldered directly on the motherboard. The size of the EEPROM can vary. Mine is (was) 32MB.

    Now questions:
    1. The original BIOS file for my mobo is 4MB in size and is stored in a 32MB EEPROM. Does anybody know what else resides in the SPI Flash EEPROM?
    2. In a BIOS file is the boot sector block mentionned above always the same size? At which address in the code does it start? I tend to believe that it is at the end of the BIOS file but need confirmation.
    3. In case of a DUAL CPU board are there 2 different EEPROM which each contains the BIOS for each CPU or one EEPROM for both BIOSes of each CPU or a single EEPROM containing a single BIOS for both CPUs?


    Thank you for sharing your knowledge.:)
     
  2. redroad

    redroad MDL Guru

    Dec 2, 2011
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    Post the board make and model. There may be a recovery partition where the the unmodded bios still is intact especially if it is a dual cpu socket board.
     
  3. DonJohn

    DonJohn MDL Junior Member

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  4. redroad

    redroad MDL Guru

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  5. DonJohn

    DonJohn MDL Junior Member

    Jan 16, 2010
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  6. redroad

    redroad MDL Guru

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    You are correct see above posts
     
  7. redroad

    redroad MDL Guru

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    This pretty much explains some of your questions

     
  8. DonJohn

    DonJohn MDL Junior Member

    Jan 16, 2010
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    No I had my questions AFTER I read what you mention. See my questions in post #1
     
  9. redroad

    redroad MDL Guru

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  10. redroad

    redroad MDL Guru

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    Do you have a floppy drive in the case?
     
  11. redroad

    redroad MDL Guru

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  12. DonJohn

    DonJohn MDL Junior Member

    Jan 16, 2010
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    Hi redroad,
    I apologize for my lack of response. I had seen your post but thought that a 4MB BIOS file won't fit on a 1.44MB floppy. I also read your last post and don't understand it. You're talking about a floppy boot disk and a (floppy) disk with the recovery bios. But the recovery bios won't fit on a floppy. It is 4MB. Then you're talking about a DOS bootable device (USB stick, CD...) and getting to a DOS prompt. But I can't get to a DOS prompt with the bricked machine. The monitor remains in sleep mode and the screen is black!! Can you please re-explain your procedure in case I don't get it? :aglerks:
     
  13. DonJohn

    DonJohn MDL Junior Member

    Jan 16, 2010
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    I just tried booting the dead machine with a bootable USB stick. I just wanted to confirm something that I had tried earlier. Results: nothing happens. Monitor remains in sleep mode and screen remains black.

    I think en4rab made the point. The first thing that gets executed when you power on a computer is the boot sector block of the BIOS. If the boot sector block of the BIOS is damaged, there's nothing you can do with that machine!!
     
  14. redroad

    redroad MDL Guru

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    One way to test put dos boot floppy into floppy drive--> boot--> guess when you think it's at A:\ drive (about 3 min.should do it) --> now hit ctrl. + alt.+ DELETE IF THE COMPUTER SHUTS DOWN THE BOOT SECTOR BLOCK IS STILL USABLE.

    I currently believe it is doable