1.2 Types of Computers

Most of us are familiar with the Personal Computer (PC) that is found in homes, schools, and businesses. However, there are other types of computers which less common than the PC. To better understand computer technology, computers are classified in different ways, with one method of classification as either digital computers or analog computers.

Digital computer computers operate on fixed states, such as voltage values of +5 or 0. In this approach, the intermediate values are not allowed. In contrast, analog systems operate on a continuous signal, allowing for a wide range of values.  For example, in analog systems, voltage values can cover a range from +5 to 0 with all intermediate values. The graph on the left show discrete (fixed values) voltage changes and the graph on the right show analog (continuous values) voltage changes.

Fig 1.2. A discrete voltage change and an analog Voltage change

Most computers today fall into the digital category, and the focus of this book will be on the concepts of digital computing. Analog computers, on the other hand, are found in specialized environments where there is a continuous stream of input to be analyzed. The slide rule shown below is an example of an analog computing device. It was commonly used before electronic calculator became common.

Fig 1.3. The slide rule. An analog computing device

General Purpose Computers

Computers can also be classified based on the type of usage as either general purpose computers or special purpose computers. General purpose computers are designed to be versatile and flexible with the ability to perform a variety of different tasks. Common examples of general purpose computers include PCs, tablets, and smartphones. These devices are designed to handle various applications and adapt to different user needs.

General purpose computers are further classified based on their size and computing capability. As a general rule the larger the physical size, the greater the computing power of the machine. This rule however is not valid when comparing computers of the past with the computers of the present. For example, desktop computers of today have much greater computing power than the large computers of the past that filled a whole room. The largest of computing devices is the mainframe computer which is used for large scale computing. Mainframe computers are used in large corporations, government agencies, and universities where there is a need for processing a large volume of information. One step below the mainframe would be the mid-sized computer or minicomputer. These are used mostly in medium sized businesses. Similarly, one step below the minicomputer is the microcomputer or the PC, which is used by individuals, small businesses, and schools. At the bottom end of the scale are the handheld computing devices such as smartphones and tablets. These are called Personal Digital Assistants (PDA) and they have become as common as the PC.

    

Fig 1.4. Types of computers. A laptop and a mainframe.

Embedded Systems

A special purpose computer is designed to perform a specific task; for example, a computing device in a car engine. These special purpose computers are usually referred to as embedded systems. These types of computing devices collect information related to a task, process the information, and produce an output that is task oriented. These embedded computing devices are present in automobiles, aircrafts, fax machines, photocopiers, etc., to enhance their operating performance. For example, a computing device present in the engine of a modern car improves and monitors its performance. In this case the computing device collects information from different sensors on the engine and then makes the necessary adjustments to keep the engine running at its best. The image on the right shows a mechanic running diagnostics on a car engine computer.

Microcontrollers

Microcontrollers are essentially computers with limited storage, processing and simple I/O functionality. Examples of such devices are the Arduino, PIC®, and Parallax® microcontrollers. Unlike PCs, laptops, and tablets, which come with some standard I/O devices like a screen, keyboard, etc., microcontrollers have no I/O devices attached to it.  They are circuit boards with ICs and connectors for power and I/O. The program to run on a microcontroller needs to be loaded on it, and this is usually done through a USB connection. The program on the microcontroller memory is run each time the microcontroller is turned on, and if it needs to be changed then the old program is erased and a new one inserted via the USB connection.

Microcontrollers are useful because they can be used to control devices. For example, a microcontroller could be used to grow plants. If the microcontroller I/O is connected to probes that measures moisture levels, lighting, and nutrient levels, then it can be used to control the amount of water, light and nutrients provided to the plants for optimal growth. If the microcontroller has network capability, then the system could be monitored and controlled from a remote location.

1.2 Practice Questions                                                                                                               

1.     Can a PC be classified as a general purpose stand-alone microcomputer?

2.     What are some advantages of distributed computing over centralized computing?

3.     What are the differences between a PDA and a PC?

4.     Explain the difference between an analog computer and a digital computer?

5.     What type of a computer is the hand held calculator?

6.     What are special purpose computers, and where are they found?

7.     What are the differences between a PC and a microcontroller?

8.     How would you classify a computing system found in a washing machine? A general purpose computer, an embedded system, or a microcontroller. Explain.