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Chapter 1. Introduction to Computers > 1.5 CLASSIFICATION OF COMPUTERS

1.5 CLASSIFICATION OF COMPUTERS

Today, computers are available in different sizes and types. One can have a computer that can fit in the palm to those that can occupy the entire room. Some computers are designed to be used by a single user only, whereas some computers can handle the needs of many users simultaneously. Computers also differ based on their data-processing abilities. In general, the computers can be classified according to purpose, data handling and functionality (see Figure 1.13).

1.5.1 Classification According to Purpose

Computers are designed for different purposes. They can be used for either general or specific purposes.

1.5.1.1 General-purpose Computers

A general-purpose computer, as the name suggests, is designed to perform a range of tasks. These computers have the ability to store numerous programs. These machines can be used for various applications, ranging from scientific to business-purpose applications. Even though such computers are versatile, they generally lack in speed and efficiency. The computers used in schools and homes are general-purpose computers.

Figure 1.13. Classification of Computers


1.5.1.2 Specific-purpose Computers

These computers are designed to handle a specific problem or to perform a single specific task. A set of instructions for the specific task is built into the machine. Hence, they cannot be used for other applications unless their circuits are redesigned, that is, they lack versatility. However, being designed for specific tasks, they can provide the result very quickly and efficiently. These computers are used for airline reservations, satellite tracking and air traffic control.

1.5.2 Classification According to Type of Data-handling Techniques

Different types of computers process the data in different manner. According to the basic data-handling techniques, computers can be classified into three categories: analog, digital and hybrid.

1.5.2.1 Analog Computers

A computing machine that operates on data in the form of continuously variable physical quantities is known as analog computer. These computers do not deal directly with the numbers. They measure continuous physical magnitudes (e.g. temperature, pressure and voltage), which are analogous to the numbers under consideration. For example, the petrol pump may have an analog computer that converts the flow of pumped petrol into two measurements: the quantity of petrol and the price of that quantity.

Analog computers are used for scientific and engineering purposes. One of the characteristics of these computers is that they give approximate results since they deal with quantities that vary continuously. The main feature of analog computers is that they are very fast in operation as all the calculations are done in 'parallel mode'. It is very easy to get graphical results directly using analog computer. However, the accuracy of analog computers is less.

1.5.2.2 Digital Computers

A computer that operates with information, numerical or otherwise, represented in a digital form is known as digital computer. Such computers process data (including text, sound, graphics and video) into a digital value (in 0s and 1s). In digital computers, analog quantities must be converted into digital quantity before processing. In this case, the output will also be digital. If analog output is desired, the digital output has to be converted into analog quantity. The components, which perform these conversions, are the essential parts or peripherals of the digital computer.

Digital computers can give the results with more accuracy and at a faster rate. The accuracy of such computers is limited only by the size of their registers and memory. The desktop PC is a classic example of digital computer.

1.5.2.3 Hybrid Computers

Hybrid computer incorporated the measuring feature of an analog computer and counting feature of a digital computer. For computational purposes, these computers use the analog components and for the storage of intermediate results, digital memories are used. To bind the powers of analog and digital techniques, that is, analog to digital and digital to analog, the hybrid computers comprehensively use converters. Such computers are broadly used in scientific applications, various fields of engineering and industrial control processes.

1.5.3 Classification According to Functionality

Based on physical size, performance and application areas, the computers are generally classified into four major categories: micro, mini, mainframe and super computers.

1.5.3.1 Micro Computers

A micro computer is a small, low-cost digital computer, which usually consists of a microprocessor, a storage unit, an input channel and an output channel, all of which may be on one chip inserted into one or several PC boards. The addition of a power supply and connecting cables, appropriate peripherals (keyboard, monitor, printer, disk drives and others), an operating system and other software programs can provide a complete micro computer system. The micro computer is generally the smallest of the computer family. Originally, these computers were designed only for individual users, but nowadays they have become powerful tools for many businesses that, when networked together, can serve more than one user. IBM-PC Pentium 100, IBM-PC Pentium 200 and Apple Macintosh are some of the examples of micro computers. Micro computers include desktop, laptop and hand-held models such as personal digital assistants (PDAs).

  • Desktop Computer: A desktop computer or personal computer (PC) is the most common type of micro computer (see Figure 1.14). It is principally intended for stand-alone use by an individual. These micro computers typically consist of a system unit, a display monitor, a keyboard, internal hard disk storage and other peripheral devices. The major criterion behind the importance of the PCs is that they are not very expensive for the individuals or for the small businesses. Some of the major personal computer manufacturers are APPLE, IBM, Dell and Hewlett-Packard.

  • Laptop: A laptop is a portable computer that a user can carry around. Since the laptop resembles a notebook, it is also known as notebooks (see Figure 1.15). They are small computers enclosing all the basic features of a normal desktop computer. The biggest advantage of laptops is that they are lightweight and can be used anywhere and at any time, especially while travelling. Moreover, they do not need any external power supply as a rechargeable battery is completely self-contained. However, they are expensive as compared to desktop computers.

Figure 1.14. Desktop Computer


Figure 1.15. Laptop


  • Hand-held Computers: A hand-held computer such as PDA is a portable computer that can be conveniently stored in a pocket (of sufficient size) and used while the user is holding it. PDAs are essentially small portable computers and are slightly bigger than the common calculators. A PDA user generally uses a pen or electronic stylus, instead of a keyboard for input. As shown in Figure 1.16, the monitor is very small and is the only apparent form of output. Since these computers can be easily fitted on the top of the palm, they are also known as palmtop computers. Hand-held computers usually have no disk drive; rather they use small cards to store programs and data. However, they can be connected to a printer or a disk drive to generate output or store data. They have limited memory and are less powerful as compared to desktop computers. Apple Newton, Casio Cassiopeia, and Franklin eBookMan are some of the examples of hand-held computers.

1.5.3.2 Mini Computers

In the early 1960s, Digital Equipment Corporation (DEC) started shipping its PDP series computer, which is described and referred as mini computer by the press. A mini computer is a small digital computer, which normally is able to process and store less data than a mainframe, but more than a micro computer, while doing so less rapidly than a mainframe but more rapidly than a micro computer. These computers are about the size of a two-drawer filing cabinet (see Figure 1.17). Generally, they are used as desktop devices that are often connected to a mainframe to perform the auxiliary operations.

Figure 1.16. Personal Digital Assistant


Figure 1.17. Mini Computer


A mini computer (sometimes called a mid-range computer) is designed to meet the computing needs of several people simultaneously in a small- to medium-sized business environment. It is capable of supporting 4 to about 200 simultaneous users. It serves as a centralized storehouse for a cluster of workstations or as a network server. Mini computers are usually multi-user systems, therefore they are used in interactive applications in industries, research organizations, colleges and universities. They are also used for real-time controls and engineering design work. High-performance workstations with graphics I/O capability use mini computers. Some of the widely used mini computers are PDP 11, IBM (8000 series) and VAX 7500.

1.5.3.3 Mainframes

A mainframe is an ultra-high-performance computer made for high-volume, processor-intensive computing (see Figure 1.18). It consists of a high-end computer processor, with related peripheral devices, capable of supporting large volumes of data processing, high-performance online transaction processing and extensive data storage and retrieval. Normally, it is able to process and store more data than a mini computer and far more than a micro computer. Mainframes are the second largest (in capability and size) of the computer family, the largest being the super computers. However, they can usually execute many programs simultaneously at a high speed, whereas super computers are designed for a single process.

Mainframe computer allows its user to maintain large information storage at a centralized location and is able to access and process this data from different computers located at different locations. It is typically used by large businesses and for scientific purposes. IBM's ES000, VAX 8000 and CDC 6600 are examples of mainframe computers.

1.5.3.4 Super Computers

Super computers are the special-purpose machines, which are specially designed to maximize the numbers of FLOPS (floating point operation per second) (see Figure 1.19). Any computer below 1 gigaflop/s is not considered a super computer. A super computer has the highest processing speed at a given time for solving scientific and engineering problems. It basically contains a number of CPUs that operate in parallel to make it faster. Its processing speed lies in the range of 400–10,000 MFLOPS (millions of floating point operation per second). Due to this feature, super computers help in many applications such as information retrieval and computer-aided design.

Figure 1.18. Mainframe Computer


Figure 1.19. Super Computer


A super computer can process a great deal of information and make extensive calculations very quickly. They can resolve complex mathematical equations in a few hours, which would have taken a scientist with paper and pencil a lifetime, or years, using a hand calculator. They are the fastest, costliest and most powerful computers available today. Typically, super computers are used to solve multivariant mathematical problems of existent physical processes such as aerodynamics, metrology and plasma physics. These are also required by the military strategists to simulate defence scenarios. Cinematic specialists use them to produce sophisticated movie animations. Scientists build complex models and simulate them in a super computer. Here, it is used to model the actions and reactions of literally millions of atoms as they interact. Super computer has limited use because of its high cost and limited market. The largest commercial use of super computers is in the entertainment/advertising industry. A few examples of super computers are CRAY-3, Cyber 205 and PARAM.

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