Karbosguide.com - Module 2b1.

About the System Bus


In this module, you can read about the following subjects, which add to our tour of the PC:

  • The boot process
  • Data on the motherboard

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  • The boot process

    The last step in the PC start-up is reading the operating system. The start-up program is instructed to find the Master Boot Record. This is located in the very first sector on either hard disk (C) or floppy drive A. From the MBR it reads the boot-strap which points to the location of the startup files of the Operating System.

    By default, the PC will look for a boot sector in floppy drive A. That is why the PC "drops dead" if there is a different diskette in A drive. If there is no diskette in A drive, the start-up program will search for the boot sector on hard drive C. When the boot sector is found, a small program segment (boot-strap) is read from there. The boot-strap then takes over control of the PC. The start-up program has done its job. Now DOS, Windows , or another operating system takes control.

    Read more about boot sectors, etc. in module 6a, which deals with file systems.

    Here is an illustration of the start-up process:


    The data flow on the motherboard

    On the motherboard, you will find the CPU, which is the "brain" of the PC and the buses. The buses are the nerve system of the motherboard. They connect the CPU to all the other components. There are at least three buses, which you can see below. You can read more about those on the following pages.

    The buses are the PC's expressways. They are "wires" on the circuit board, which transmit data between different components.

    One "wire" can move one bit at a time. In the following text, we start from a typical Pentium board. We will look at buses, chip sets and CPUs. Here is an illustration of some of the motherboard "logic." You can print it:


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    Learn more

    Read more about the motherboards chip set in module 2d

    Read more about RAM in module 2e

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