3. CPU Museum and Silicon Zoo

CPU Museum is at

• Intel CPU Museum http://www.intel.com/intel/intelis/museum
• Intel - History of Microprocessors http://www.intel.com/intel/museum/25anniv
• Virtual Museum of Computing http://www.museums.reading.ac.uk/vmoc
• Silicon Zoo http://micro.magnet.fsu.edu/creatures/index.html
• Intel - How the Microprocessors work http://www.intel.com/education/mpuworks
• Simple course in Microprocessors http://www.hkrmicro.com/course/micro.html

3.1 How Transistors work

Microprocessors are essential to many of the products we use every day such as TVs, cars, radios, home appliances and of course, computers. Transistors are the main components of microprocessors. At their most basic level, transistors may seem simple. But their development actually required many years of painstaking research. Before transistors, computers relied on slow, inefficient vacuum tubes and mechanical switches to process information. In 1958, engineers (one of them Intel founder Robert Noyce) managed to put two transistors onto a silicon crystal and create the first integrated circuit that led to the microprocessor.

Transistors are miniature electronic switches. They are the building blocks of the microprocessor which is the brain of the computer. Similar to a basic light switch, transistors have two operating positions, on and off. This on/off, or binary functionality of transistors enables the processing of information in a computer.

How a simple electronic switch works:

The only information computers understand are electrical signals that are switched on and off. To comprehend transistors, it is necessary to have an understanding of how a switched electronic circuit works. Switched electronic circuits consist of several parts. One is the circuit pathway where the electrical current flows - typically through a wire. Another is the switch, a device that starts and stops the flow of electrical current by either completing or breaking the circuit's pathway. Transistors have no moving parts and are turned on and off by electrical signals. The on/off switching of transistors facilitates the work performed by microprocessors.

3.2 How a Transistors handles information

Something that has only two states, like a transistor, can be referred to as binary. The transistor's on state is represented by a 1 and the off state is represented by a 0. Specific sequences and patterns of 1's and 0's generated by multiple transistors can represent letters, numbers, colors and graphics. This is known as binary notation

3.3 Displaying binary information

Spell your name in Binary:

Each character of the alphabet has a binary equivalent. Below is the name JOHN and its equivalent in binary.

        J  0100 1010
        O  0100 1111
        H  0100 1000
        N  0100 1110

Scroll down to the Binary Chart below to see the complete alphabet in binary.

3.4 What is a Semi-conductor?

Conductors and insulators :

Many materials, such as most metals, allow electrical current to flow through them. These are known as conductors. Materials that do not allow electrical current to flow through them are called insulators. Pure silicon, the base material of most transistors, is considered a semiconductor because its conductivity can be modulated by the introduction of impurities.

Anatomy of Transistor

Semiconductors and flow of electricity

Adding certain types of impurities to the silicon in a transistor changes its crystalline structure and enhances its ability to conduct electricity. Silicon containing boron impurities is called p-type silicon - p for positive or lacking electrons. Silicon containing phosphorus impurities is called n-type silicon - n for negative or having a majority of free electrons

A Working Transistor

A Working transistor - The On/Off state of Transistor

Transistors consist of three terminals; the source, the gate and the drain.

In the n-type transistor, both the source and the drain are negatively-charged and sit on a positively-charged well of p-silicon.

When positive voltage is applied to the gate, electrons in the p-silicon are attracted to the area under the gate forming an electron channel between the source and the drain.

When positive voltage is applied to the drain, the electrons are pulled from the source to the drain. In this state the transistor is on.

If the voltage at the gate is removed, electrons aren't attracted to the area between the source and drain. The pathway is broken and the transistor is turned off.

Impact of Transistors

The Impact of Transistors - How microprocessors affect our lives.

The binary function of transistors gives micro- processors the ability to perform many tasks; from simple word processing to video editing. Micro- processors have evolved to a point where transistors can execute hundreds of millions of instructions per second on a single chip. Automobiles, medical devices, televisions, computers and even the Space Shuttle use microprocessors. They all rely on the flow of binary information made possible by the transistor.