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difference between ROM BIOS and CMOS RAM

Discussion in 'PC Hardware' started by kmsk, 2009/03/15.

  1. 2009/03/15
    kmsk

    kmsk Inactive Thread Starter

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    Hi,

    On any motherboard we usually see ROM Bios of different manufacturers.
    I have read in books that the bios setup parameters like deciding boot sequence
    is stored in CMOS Ram which holds this information even if we shut off the PC supported by Battery . I can see the battery on my motherboard. But i could not locate CMOS RAM.Is CMOS Ram a chip on the motherboard. Can you pls tell me where to find it.
     
    kmsk,
    #1
  2. 2009/03/15
    PeteC

    PeteC SuperGeek Staff

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    Yes.

    Generally speaking the BIOS chip will have a sticker on it with the manufacturer's name on it - AMI, Phoenix, Award .....

    OTH your motherboard manual should give you a diagram showing the placement of the various chips.

    From memory the BIOS chip is often in the left hand upper quartile of the board, close to the back of the case.
     

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  4. 2009/03/16
    Bill

    Bill SuperGeek WindowsBBS Team Member

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    There are some commonly mixed up terms we need to set clear first.

    The below are hardware/electronic devices:
    RAM - Random Access Memory (a memory device used for system RAM, not the BIOS).

    ROM - Read Only Memory (devices programmed at the factory, cannot be changed by users).

    CMOS - Complementary Metal Oxide Semiconductor - a special kind of memory device that loses all its stored data almost instantly when voltage is removed by battery removal, or BIOS reset - note a BIOS reset does not reset the BIOS memory module, it "clears the CMOS" by forcing it to forget any custom settings.

    EEPROM - Electrically Erasable Programmable Read Only Memory - also known as a firmware device - these devices are used to store (flash) the BIOS program into semi-permanent memory.​

    The BIOS (Basic Input Output System) is a software program that has been programmed (flashed) into an EEPROM module (integrated circuit, IC) mounted on the motherboard. This program is not lost when all power is removed. This program is written by the BIOS/chipset/motherboard makers. It takes a special program to rewrite the BIOS firmware.

    The CMOS is used by the motherboard chipset to save custom settings - changes to the BIOS firmware defaults, such as date and time, boot order, on-board device management, etc.

    The CMOS memory module and the BIOS firmware EEPROM memory module work together to configure the motherboard to work with the attached hardware.
     
    Bill,
    #3

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