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 lacked 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.

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

A computing machine that works on the principle of measuring, in which the measurements obtained are translated into desired data is known as analog computer. Modern analog computers usually employ electrical parameters,such as voltages,resistances or currents,to represent the quantities being manipulated. Such computers do not deal directly with the numbers. They measure continuous physical magnitudes (such as 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 for that quantity.

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 that perform these conversions,are the essential parts or peripherals of the digital computer.

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

A hybrid computer incorporates the measuring feature of an analog computer and the 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. In order to bind the powers of analog and digital techniques, hybrid computers comprehensively use analog-to-digital and digital-to-analog converters. Such computers are broadly used for scientific applications, various fields of engineering and in industrial control processes.

Based on physical size, performance and application areas, we can divide computers generally into four major categories: micro, mini, mainframe, and super 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, etc.), 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, they were designed for individual users only, 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 computers.

1. Desktop Computer: Desktop computer or PC (Personal Computer) is the most common micro computer. 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 to purchase by the individuals or the small businesses. Some of the major personal computer manufacturers are APPLE, IBM, Dell, and Hewlett-Packard.
2. Laptop: A laptop is a portable computer, that is, a user can carry it around. Since the laptop computer resembles a notebook, they are also known as notebooks. Laptops are small computers enclosing all the basic features of a normal desktop computer. The biggest advantage of this computer is that one can use this computer anywhere and at anytime, specially when one is travelling and does not have a proper place to keep it. Moreover, these computers do not need any external power supply as a rechargeable battery is self-contained in them. These computers are expensive as compared to desktop computers.
3. Hand-held Computers: A hand-held, also called Personal Digital Assistant (PDA), is a computer that can conveniently be 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 palmtop, they are also known as palmtop computers. Hand-held computers usually have no disk drives, rather they use small cards to store programs and data. However, they can be connected to printer or a disk drive to generate output or store data. They have limited memory and are less powerful as compared to desktop computers. Some examples of PDAs are Apple Newton, Casio Cassiopeia, and Franklin eBookMan.

Mini Computers

A super computer can process a great deal of information and make extensive calculations very, 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 multi-variant mathematical problems of existent physical processes, such as aerodynamics, metrology, and plasma physics.

The classification of computers offers insight into the vast and diverse world of computing devices. Each type of computer is optimized to excel in particular areas, whether it's processing massive data sets,serving as a personal productivity tool, or controlling industrial machinery.Understanding these classifications helps us choose the right computer for the job and appreciate the incredible versatility and impact of computing technology in our lives.