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

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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

    Jan 16, 2010
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  4. redroad

    redroad MDL Guru

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    I have 2 supermicro modded boards but they are x6 and x7 series boards. I am unable to down load the manual from your board from supermicro at the moment but on my boards there are two silver pads on the board to which you touch both pads bridging them resetting the bios. The power is unplugged when you do this of course. These boards are great and have built in save your axx options so hopefully we can get you going again. Read the manual for bios recovery here http://www.supermicro.com/support/resources/results.cfm and I'll see if can add anything else. BTW akcent did the mods on both my boards so I really don't know what happened but with a nice board like that one we better get it operational if we can
     
  5. redroad

    redroad MDL Guru

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  6. DonJohn

    DonJohn MDL Junior Member

    Jan 16, 2010
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    Thank you for your nice words.
    The pads you're referring to are for clearing CMOS. As far as I understand but I'm not sure and that's why I opened this thread, CMOS are settings you can set by yourself. These are the settings you can change when entering the BIOS at startup (time, boot priority...). Clearing CMOS is just like resetting the parameters to their default. Clearing CMOS doesn't mean re-flashing the original BIOS that would be saved somewhere. Correct me if I'm wrong...

     
  7. DonJohn

    DonJohn MDL Junior Member

    Jan 16, 2010
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  8. redroad

    redroad MDL Guru

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    You are correct see above posts
     
  9. redroad

    redroad MDL Guru

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    This pretty much explains some of your questions

     
  10. 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
     
  11. redroad

    redroad MDL Guru

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    #12 redroad, Mar 22, 2012
    Last edited: Mar 22, 2012
    In your case are we talking about a U(efi) bios?

    Answers to qusestions

    1) I believe the 4mb block is the boot sector block and contains the codes for both processors
    2) size is set by manufacturer and varies accordingly
    3) answered in 1

    So am I to understand correctly that you performed the following steps 1-12 here
    http://www.google.com/url?sa=t&rct=j&q=supermicro bios recovery&source=web&cd=3&ved=0CDMQFjAC&url=http%3A%2F%2Fwww.supermicro.com%2Fmanuals%2Fother%2Fuefi_bios_recovery.pdf&ei=XqhrT9yaE-2o0AHsg7nZBg&usg=AFQjCNF6tgsFztGPS82yyDLnj4aMCQSB6w&cad=rja
     
  12. DonJohn

    DonJohn MDL Junior Member

    Jan 16, 2010
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    My BIOS is not a UEFI BIOS. It is a regular AMI BIOS. But I did perform similar steps as described in the document you mention. I downloaded the original BIOS, renamed the file SUPER.ROM, copied it in the root directory of an empty USB stick. I plugged this USB stick into the X8DTi and powered it on. But the BIOS does not recover. The power light of the board comes on, the fans spin and the board accesses the USB stick. The USB stick light flashes with the same pattern for ever. The monitor remains in sleep mode all the time (power button does not change color as when it is active) and the screen is completely black.

    Because the USB stick light flashes I thought the board did not find the file it was looking for. So I repeated the process with a file named AMIBOOT.ROM and with a file that kept the original name. But it is not working. In the BIOS modded by Akcent I verified that the Boot sector was still there and I found the string SUPER.ROM. However, Akcent confirmed that the mod did go wrong. Hence my questions about where to find the boot sector block in the BIOS. That way I could have compared the boot sector from Akcent modded BIOS with the original. It should be kept in mind that the process of flashing Akcent faulty BIOS completed successfully.

     
  13. redroad

    redroad MDL Guru

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    Do you have a floppy drive in the case?
     
  14. en4rab

    en4rab MDL Novice

    Oct 27, 2009
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    The first question is caused by the naming convention of the chips, the flash chip size is given as the number of bits it can store eg 32 megabit, and your bios image size is listed by bytes so is 4 mega bytes, since there are 8 bits in a byte 32/8=4 so your flash chip is the same size as your bios file. If you wish to be really specific its actually 32 mebibits (Mib) and 4 mebibytes (MiB) but that is the new ISO way of naming things and is a world of pain but if you want to read more its here: http://en.wikipedia.org/wiki/Binary_prefix#Specific_units_of_IEC_60027-2_A.2_and_ISO.2FIEC_80000

    I havent looked at bootblock sectors enough to comment but i suspect their size (or at least the space treated in the bios as bootblock) will be fixed for a particular type of bios eg award, pheonix and it should be at the end of the bios file as upon reset an x86 cpu starts executing at 0xFFFFFFF0 which is 16 bytes before the end of the bios chip. At this address is normally a jmp instruction that jumps to the start of the actual bootblock code.

    The dual CPU dell i have here has one bios chip, I have no idea about the specifics of how booting is handled, I guess there is a master cpu that boots the bios and brings up the second cpu, but it could use witchcraft for all i know :) but my machine has only one bios chip with only one copy of the bios in it.
     
  15. DonJohn

    DonJohn MDL Junior Member

    Jan 16, 2010
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    Thank you en4rab. Your post brings answers and good points.

    I didn't pay attention to the bit and byte stuff. I'm fully aware of the difference but I overlooked it here:bash:. So the 4MB BIOS file fits perfectly in the 32Mbit EEPROM. Here's an example of the kind of EEPROM chip that contains the BIOS of a motherboard. http://www.atmel.com/Images/doc3669.pdf
     
  16. redroad

    redroad MDL Guru

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    #17 redroad, Mar 23, 2012
    Last edited: Mar 23, 2012
    maybe you didn't see the my post

    Do you have a floppy in the case? If you do then create a dos boot disk and a disk with the recovery bios and then do what is listed but you will be doing it blind.

    a). Save this file to your computer.

    b). Extract the files to a DOS bootable device (such as a bootable USB stick, CD, or floppy drive).

    c). Boot to a DOS prompt and type AMI.BAT filename.xxx.(example AMI.BAT X8DT30.311)

    d). Do not interrupt the process until the flashing is complete.

    e). If the computer pauses, please wait until it starts to program.

    f). Reboot the system by pressing "CTRL+ALT+DEL" .

    g). Press "F1" to the BIOS screen when system reboot and shows the message "Press F1 to go to setup or press F2 to continue.

    h). Press "F9" to "load the default" in the BIOS screen.

    i). Press "F10" to "Save and Exit"

    Don't ask me why this works better with floppy drive but it does and have successfully done this process when in your situation several times after using usb or cd first. IMHO floppy is still the best for Bios flash.

    If you don't want to do it blind then Recover the Boot Sector Using a Serial Port. as specified in this document which I had already posted. Starting on page 2

    http://www.google.com/url?sa=t&rct=j&q=supermicro bios recovery&source=web&cd=1&ved=0CCYQFjAA&url=http%3A%2F%2Fwww.mullet.se%2Fsupport%2FAMI_BIOS_Recovery.pdf&ei=XqhrT9yaE-2o0AHsg7nZBg&usg=AFQjCNGsHq_Jmb3WTa80G3lLDK5-ymvamQ&cad=rja
     
  17. 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:
     
  18. 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!!
     
  19. 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