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.

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:

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 goback 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:

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. Joystick Monitor Printer Scanner Loudspeakers External drives External tape station External modem

Introduction

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: Small inexpensive, mass produced computers. They work on DOS, Windows , or similar operating systems. They are used for standard applications.

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?

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:

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, we shall start with a review of that.