* The electronic computer has been around for over half a century, but its ancestors have been around for 2000 years. However, only in the last 40 years has it changed society.
* From the first wooden abacus to the latest high-speed microprocessor, the computer has changed nearly every aspect of our lives for the better.
* Computer indeed derives its name from its essential function, namely, to compute.
* Any computation requires primary data and operations performed between them.
* Receiving data, processing them, keeping in memory the data at different stages of operation, having some set of data that is fundamental to all operations and giving outcomes of operations.
Essentially a computer means a system of components:
a. to input data and display output i.e. Input and Output devices.
b. processing unit called the Central Processing Unit (CPU).
c. The memory space which can be Read Only Memory (ROM) or Random Access Memory (RAM).
The memory in terms of capacity (space) and speed and the processing capacity of the CPU (speed with which it processes) characterise computers and distinguish them.
1. Analogue Computers: They work on continuous variables like waves of the signal, their amplitude, etc.
2. Digital Computers: They work on the principle of binary digits i.e. 0 and 1. Any value or symbol is represented through a binary value.
3. Hybrid Computers: They are a combination of good features of analogue and digital computers. Digital counterparts convert the analogue signals to perform robotics and other process control. Hybrid computers are used to control air traffic and radar of national defence.
Based on capacity, speed and reliability Digital Computers are classified into three categories:
* The term “Microcomputer” was introduced with the advent of single chip Large Scale Integrated Circuit (LSIC) computer processors.
* It is the smallest single user computer and its CPU is a microprocessor. It can perform the same operations and can use the same type of instructions as other computers.
* These are the most frequently used computers, better known by the name ‘Personal Computers.’
a. Desktop computers:
* Desktop computers are larger and not meant to be portable. They usually sit in one place on a desk or table and are plugged into a wall outlet for power.
* When this case lies flat on the desk then it is generally referred to as a Desktop Model else when it stands vertically on the desk in the form of a tower, it is referred to as a Tower Model.
* The computer usually has a separate monitor. A separate keyboard and mouse allow the user to input data and commands.
b. Laptop: This is a small, portable computer small enough that it can sit on the lap. Nowadays laptop computers are also called notebook computers.
* It is so small that it literally fits in a palm, hence, referred to as palmtop.
* Compared to full-size computers, palmtops are severely limited, but they are practical for certain functions such as phonebooks and calendars.
* Sometimes these are also called pocket computers.
d. Personal Digital Assistants:
* Palmtops that use a pen rather than a keyboard for input are often called PDAs.
* PDA can function as a cellular phone, fax sender and personal organiser. a PDA was pioneered by Apple, which introduced the Newton Message Pad in 1993.
e. Tablet PC: It is a notebook slate-shaped mobile computer which is equipped with a touchscreen or graphics table which allows the user to operate the computer with a digital pen or stylus or fingertip.
* A powerful, single user computer. It has a more powerful microprocessor a higher quality monitor used in computer aided design and other applications requiring a high end, usually expensive, machine with considerable calculating or graphics capability.
II. Mini Computer:
* It is a multi user computer capable of supporting up to hundreds of users simultaneously.
* They are usually more powerful compared to microcomputers.
* Minicomputers are also known as mid range computers as their cost and computing powers lie in the middle range between micro and mainframe computers.
* Minicomputers are used for multi users and interactive applications.
III. Mainframe Computer:
* A powerful multi user computer, the mainframe computer, is capable of supporting many hundreds or thousands of users simultaneously.
* They are capable of faster processing and greater storage area.
* They are used in research organisations, large industries, large businesses and government organisations, banks and airline reservation where a large database is required.
Characteristics of computers
Speed: Computers work at an incredible speed. A powerful computer is capable of performing about 3-4 million simple instructions per second.
Accuracy: Computers are also accurate. Errors that may occur can almost always be attributed to human error (inaccurate data, poorly designed system or faulty instructions/ programs written by the programmer).
Diligence: Unlike human beings, computers are highly consistent. They do not suffer from human traits of boredom and tiredness resulting in lack of concentration.
Versatility: Computers are versatile machines and are capable of performing any task as long as it can be broken down into a series of logical steps. The presence of computers can be seen in almost every sphere of life.
Storage capacity: Computers can store large volumes of data. A piece of information once recorded (or stored) in the computer, can never be forgotten and can be retrieved almost instantaneously.
* A computer cannot act on situations that are not fed or programmed into them.
* A computer does not have feelings/ Emotional Quotient.
* A computer cannot decide on its own ~ Lack of decision making.
* A computer might be an automated machine still, it requires human assistance.
Evolution of computers
1. Vacuum tubes:
Main Features: Bulky, slow, unreliable, consume more space and power Software: Machine language and assembly language. Memory and I/O devices: Limited core memory, input through punch cards. Type of computer: Analogue.
Main Features: Less power consumption, smaller in size. Software: High Level Languages (HLLs) like FORTRAN, Pascal, COBOL, etc.
Memory and I/O devices: Magnetic core memory as main memory, magnetic tapes and disks. Type of Computer: Analogue.
3. Integrated Circuits (ICs):
Main Features: More memory capacity, much smaller in size and weight. Software: General purpose HLL, concurrent programming. Memory and I/O devices: Semiconductor memory as main memory, hard disks as secondary. Type of computer: Digital.
4. Very Large Scale Integration (VLSI):
Main Features: Development of microproces sor, more speed and reliability.
Software: Web based technologies, very user friendly and sophisticated, artificially intelligent software.
Memory and I/O devices: Optical disks, VCDs, DVDs, blue ray disks and high capacity hard disks.
Type of computer: Digital
5. Ultra - Large Scale Integration (ULSI):
Main Features: Much faster and very powerful.
Software: Being developed.
Memory and I/O devices: Being developed.
* The term server actually refers to a computer’s function rather than to a specific kind of computer.
* A server runs a network of computers.
* It handles the sharing of equipment like printers and the communication between computers on the network.
* For such tasks a computer would need to be somewhat more capable than a desktop computer.
* The Super Computer which is somewhat similar to the mainframe computer.
* These are largest, fastest and most expensive.
* They are used for massive data processing and solving very complicated problems like weather forecasting, weapons research and development, racketing, atomic, nuclear and plasma physics.
* The processing speed of super computers lies in the range 400-10000 Million Instructions Per Sec (MIPS).