KarbosGuide.com. Module 2a.1

The PC and its motherboard

The contents:

  • Introduction to the PC
  • The PC construction
  • The motherboard (motherboard)
  • POST and other ROM (BIOS etc.)
  • Next page
  • Previous page

  • Please click to support our work!

    Introduction to the PC

    The technical term for a PC is micro data processor . That name is no longer in common use. However, it places the PC in the bottom of the computer hierarchy:

  • Supercomputers and Mainframes are the largest computers - million dollar machines, which can occupy more than one room. An example is IBM model 390.

  • Minicomputers are large powerful machines. They typically serve a network of simple terminals. IBM's AS/400 is an example of a minicomputer.

  • Workstations are powerful user machines. They have the power to handle complex engineering applications. They use the UNIX or sometimes the NT operating system. Workstations can be equipped with powerful RISC processors like Digital Alpha or MIPS.

  • The PCs are the Benjamins in this order: Small inexpensive, mass produced computers. They work on DOS, Windows , or similar operating systems. They are used for standard applications.

    The point of this history is, that Benjamin has grown. He has actually been promoted to captain! Todays PCs are just as powerful as minicomputers and mainframes were not too many years ago. A powerful PC can easily keep up with the expensive workstations. How have we advanced this far?

    The PC's success

    The PC came out in 1981. In less than 20 years, it has totally changed our means of communicating. When the PC was introduced by IBM, it was just one of many different micro data processors. However, the PC caught on. In 5-7 years, it conquered the market. From being an IBM compatible PC, it became the standard.

    If we look at early PCs, they are characterized by a number of features. Those were instrumental in creating the PC success.

  • The PC was from the start standardized and had an open architecture.
  • It was well documented and had great possibilities for expansion.
  • It was inexpensive, simple and robust (definitely not advanced).

    The PC started as IBM's baby. It was their design, built over an Intel processor (8088) and fitted to Microsoft's simple operating system MS-DOS.

    Since the design was well documented, other companies entered the market. They could produce functionable copies (clones) of the central system software (BIOS). The central ISA bus was not patented. Slowly, a myriad of companies developed, manufacturing IBM compatible PCs and components for them.

    The Clone was born. A clone is a copy of a machine. A machine, which can do precisely the same as the original (read Big Blue - IBM). Some of the components (for example the hard disk) may be identical to the original. However, the Clone has another name (Compaq, Olivetti, etc.), or it has no name at all. This is the case with "the real clones." Today, we differentiate between:

  • Brand names, PCs from IBM, Compaq, AST, etc. Companies which are so big, so they develop their own hardware components.

  • Clones, which are built from standard components. Anyone can make a clone.

    Since the basic technology is shared by all PCs, I will start with a review of that.

    The PC construction

    The PC consists of a central unit (referred to as the computer) and various peripherals. The computer is a box, which contains most of the working electronics. It is connected with cables to the peripherals.

    On these pages, I will show you the computer and its components. Here is a picture of the computer:

    Here is a list of the PC components. Read it and ask yourself what the words mean. Do you recognize all these components? They will be covered in the following pages.

    Components in the central unit - the computer Peripherals
    The motherboard: CPU, RAM, cache,
    ROM chips with BIOS and start-up programs.
    Chip sets (controllers). Ports, buses and expansion slots.

    Drives: Hard disk(s), floppy drive(s), CD-ROM, etc.

    Expansion cards: Graphics card (video adapter),
    network controller, SCSI controller.
    Sound card, video and TV card.
    Internal modem and ISDN card.

    Keyboard and mouse.
    External drives
    External tape station
    External modem

    So, how are the components connected. What are their functions, and how are they tied together to form a PC? That is the subject of Click and Learn. So, please continue reading...

    The von Neumann Model of the PC

    Computers have their roots 300 years back in history. Mathematicians and philosophers like Pascal, Leibnitz, Babbage and Boole made the foundation with their theoretical works. Only in the second half of this century was electronic science sufficiently developed to make practical use of their theories.

    The modern PC has roots that go back to the USA in the 1940s. Among the many scientists, I like to remember John von Neumann (1903-57). He was a mathematician, born in Hungary. We can still use his computer design today. He broke computer hardware down in five primary parts:

  • CPU
  • Input
  • Output
  • Working memory
  • Permanent memory

    Actually, von Neumann was the first to design a computer with a working memory (what we today call RAM). If we apply his model to current PCs, it will look like this:

    All these subjects will be covered.

    Data exchange - the motherboard

    The ROM chips contain instructions, which are specific for that particular motherboard. Those programs and instructions will remain in the PC throughout its life; usually they are not altered.

    Primarily the ROM code holds start-up instructions. In fact there are several different programs inside the start-up instructions, but for most users, they are all woven together. You can differentiate between:

  • POST (Power On Self Test)
  • The Setup instructions, which connect with the CMOS instructions
  • BIOS instructions, which connect with the various hardware peripherals
  • The Boot instructions, which call the operating system (DOS, OS/2, or Windows )

    All these instructions are in ROM chips, and they are activated one by one during start-up. Let us look at each part.

    The suppliers of system software

    All PCs have instructions in ROM chips on the motherboard. The ROM chips are supplied by specialty software manufacturers, who make BIOS chips. The primary suppliers are:

  • Phoenix
  • AMI ( American Megatrends )
  • Award

    You can read the name of your BIOS chip during start-up. You can also see the chip on the system board. Here is a picture (slightly blurred) of an Award ROM chip:

    Here is an AMI chip with BIOS and start-up instructions:

    Let us look at the different components inside the ROM chip.

  • Next page
  • Previous page

    Learn more

    Read more about the boot process and system bus in Module 2b

    Read more about I/O buses in module 2c

    Read more about the motherboard chip set in module 2d

    Read more about RAM in module 2e

    Read about EIDE in module 5b

    I also recommend two books for further studies. Gunnar Forst: "PC Principles", from MIT is excellent. Also "The Winn L. Rosch Hardware Bible" from Brady covers the same subjects. Also "PC Intern" from Abacus is fine.

    Links to BIOS information:


    [Main page]
    [Karbo's Dictionary]
    [The Software Guides]

    Copyright (c) 1996-2005 by Michael B. Karbo. www.karbosguide.com.