Analog Computers

Analog Computer is a computing device that works on continuous range of values. The results given by the analog computers will only be approximate since they deal with quantities that vary continuously. It generally deals with physical variables such as voltage, pressure, temperature, speed, etc.


Digital Computers

On the other hand a digital computer operates on digital data such as numbers. It uses binary number system in which there are only two digits 0 and 1. Each one is called a bit.

The digital computer is designed using digital circuits in which there are two levels for an input or output signal. These two levels are known as logic 0 and logic 1. Digital Computers can give more accurate and faster results.

Digital computer is well suited for solving complex problems in engineering and technology. Hence digital computers have an increasing use in the field of design, research and data processing.

Based on the purpose, Digital computers can be further classified as:

  • General Purpose Computers
  • Special Purpose Computers

Special purpose computer is one that is built for a specific application. General purpose computers are used for any type of applications. They can store different programs and do the jobs as per the instructions specified on those programs. Most of the computers that we see today, are general purpose computers.


Hybrid Computers

A hybrid computer combines the desirable features of analog and digital computers. It is mostly used for automatic operations of complicated physical processes and machines. Now-a-days analog-todigital and digital-to-analog converters are used for transforming the data into suitable form for either type of computation.

For example, in hospital’s ICU, analog devices might measure the patient’s temperature, blood pressure and other vital signs. These measurements which are in analog might then be converted into numbers and supplied to digital components in the system. These components are used to monitor the patient’s vital sign and send signals if any abnormal readings are detected. Hybrid computers are mainly used for specialized tasks.



 Types of Computers based on Configuration

There are four different types of computers when we classify them based on their performance and capacity. The four types are

  • Micro/Personal Computers
  • Mini Computers
  • Mainframe Computers
  • Super Computers

  • Personal/Microcomputer: A small, single-user computer based on a microprocessor.
  • Minicomputer: A multi-user computer capable of supporting up to hundreds of users simultaneously.
  • Mainframe: A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.
  • Supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second.


Micro Computers

A microcomputer is also known as PC, which is the most popular form of the computer in use today. The invention of microprocessor (single chip CPU) gave birth to the much cheaper microcomputers. It can be defined as a small, relatively inexpensive computer designed for an individual user. In price, personal computers range anywhere from a few hundred pounds to over five thousand pounds. All are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet and database management applications. Although personal computers are designed as single-user systems, these systems are normally linked together to form a network. In terms of power, nowadays high-end models of the Macintosh and PC offer the same computing power and graphics capability as low-end workstations by Sun Microsystems, Hewlett-Packard, and DELL.

They are further classified into:-

  • Tower Model
  • Desktop Computers
  • Laptop Computers
  • Subnotebook Computer
  • Handheld Computers(PDAs)


Tower model: The term refers to a computer in which the power supply, motherboard, and mass storage devices are stacked on top of each other in a cabinet. This is in contrast to desktop models, in which these components are housed in a more compact box. The main advantage of tower models is that there are fewer space constraints, which makes installation of additional storage devices easier.

Desktop Computers: Today the Desktop computers are the most popular computer systems. These desktop computers are also known as personal computers or simply PCs. They are usually easier to use and more affordable. They are normally intended for individual users for their word processing and other small application requirements.

Laptop Computers: Laptop computers are portable computers. They are lightweight computers with a thin screen. They are also called as notebook computers because of their small size. They can operate on batteries and hence are very popular with travelers. The screen folds down onto the keyboard when not in use. 

Subnotebook computer: A portable computer that is slightly lighter and smaller than a full-sized notebook computer. Typically, subnotebook computers have a smaller keyboard and screen, but are otherwise equivalent to notebook computers.                                                                                                                        

Handheld Computers: Handheld computers or Personal Digital Assistants (PDAs) are pen-based and also battery-powered. They are small and can be carried anywhere. They use a pen like stylus and accept handwritten input directly on the screen. They are not as powerful as desktops or laptops but they are used for scheduling appointments, storing addresses and playing games. They have touch screens which we use with a finger or a stylus. The field of PDA was pioneered by Apple Computer, which introduced the


It is a midsize computer which is small, general-purpose compute. A typical mini system is more expensive than PC. It exceed a PC in Storage capacity and speed. While most PCs are oriented towards single users, mini systems are designed to handle the needs of multiple user simultaneously, wherein more than one person uses a minicomputer at the same time. This is possible because minicomputer are multiprocessing systems that are capable of supporting more than one program at the same time. A minicomputer is a multi-processing system capable of supporting from up to 250 users simultaneously.



Mainframe is a very large in size and an expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. Mainframe executes many programs concurrently. Mainframes support many simultaneous programs execution. A mainframe (also known as “big iron”) is a highperformance computer used for large-scale computing purposes that require greater availability and security than a smaller-scale machine can offer. Historically, mainframes have been associated with centralized rather than distributed computing, although that distinction is blurring as smaller computers become more powerful and mainframes become more multi-purpose. Today, IBM emphasizes that their mainframes can be used to serve distributed users and smaller servers in a computing network. A single mainframe computer can perform the work done by the dozens and hundreds of smaller servers. Computers like IBM 1401, ICL 2950/10, etc. come under this category. Latest released   mainframe Computer is the IBM zBC12.


Special Purpose Computer


Workstations generally come with a large, high-resolution graphics screen, large amount of RAM, inbuilt network support, and a graphical user interface. Most workstations also have a mass storage device such as a disk drive, but a special type of workstation, called a diskless workstation, comes without a disk drive.

Common operating systems for workstations are UNIX and Windows NT. Like PC, Workstations are also single-user computers. However, workstations are typically linked together to form a local-area network, although they can also be used as stand-alone systems.



Supercomputers are one of the fastest computers currently available. Supercomputers are very expensive and are employed for specialized applications that require immense amounts of mathematical calculations (number crunching). For example, weather forecasting, scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data (e.g. in petrochemical prospecting). China’s Tianhe2 supercomputer is the fastest in the world at 33.86 petaFLOPS, or 33.86 quadrillion floating point operations per second.  

Functionalities of a computer

Any digital computer carries out five functions in gross terms:

  • Takes data as input.
  • Stores the data/instructions in its memory and can use them when required.
  • Processes the data and converts it into useful information.
  • Outputs the information.
  • Controls all the above four steps.


Before we go for a further explanation of components lets discuss the logical structure. All types of computers follow a same basic logical structure and perform the following five basic operations for converting raw input data into information useful to their users


Input Unit

This unit contains devices with the help of which we enter data into computer. This unit makes link between user and computer. The input devices translate the human being information into the form understandable by computer.

CPU (Central Processing Unit)

CPU is considered as the brain of the computer. CPU performs all types of data processing operations. It stores data, intermediate results and instructions (program). It controls the operations of all parts of computer.

CPU itself has the following three components

  • ALU (Arithmetic Logic Unit)
  • Memory Unit
  • Control Unit

Output Unit

Output unit consists of devices with the help of which we get the information from computer. This unit is a link between computer and users. Output devices translate the computer’s output into the form understandable by users.