There are 3 types of electronic computers based on the technology being used:-

1. Analog Computers
2. Digital Computers
3. Hybrid Computers

1. Analog Computers:- Analog Computers are computing device that works on continuously changeable aspects. The analog computers give approximate results. It generally deals with physical variables such as voltage, pressure, temperature, speed, etc. The accuracy of an analog computer is less as compared to digital computers.

2. Digital Computers:- A digital computer operates on digital data such as numbers. It uses a binary number system in which there are only two digits 0 and 1. Digital computers are more accurate than analog computers. Digital computers are made for both general purpose and special purpose.

A special-purpose computer is one that is built for a specific application. General-purpose computers are used for any type of application.

3. Hybrid Computers:- A hybrid computing system is a combination of analog and digital computers. It has the speed of an analog computer and the accuracy of a digital computer. It may accept digital or analog signals but an extensive conversion of data from digital to analog and analog to digital has to be done.

Classification of  Digital Computers

Based on performance, size, cost, and capacity, digital computers are classified into four different types: Super Computers, Mainframe Computers, Mini Computers, and Micro Computers.

(1) Mainframe Computer:- Mainframe computers are capable of processing data at very high speeds- millions of instructions per second. Mainframe computer setup costs very high. These computers are large and very powerful computers with very high memory capacity. These can process huge databases such as census at an extremely fast rate. They are suitable for big organizations, banks, industries, etc.

(2) Mini Computers:- Mini Computers are smaller than mainframe computers. Mini Computers are a multi-user and time-sharing system. These are mainly used in an organization where computers installed in various departments are interconnected. Mini Computers are widely used in industries, small businesses, etc.

(3) Micro Computers:- Micro Computer is a general-purpose computer. These are also known as Personal Computers. This type of digital computer uses a microprocessor and includes both desktops and laptops. The cost of these computers can a few thousand rupees. Microcomputers are used in homes or personal business.

(4) Super Computers:- The term Super Computers is used for computers with the great operating speed and Power. Super Computers are the fastest computer in all types. These are the most expensive computers because they use the latest technology to achieve superior performances. They are used only for limited applications like weather forecasting, design of drugs, scientific research centers, and simulation of complex problems.

 

When the computer is switched on, a copy of the boot program is brought from ROM into
the main memory and all operating system files load into the RAM. This process is called booting. 

Booting Process is of two types – Warm and Cold

Cold Booting: When the system starts from initial state i.e. it is switched on, we call it
cold booting or Hard Booting.

Warm Booting: When the system restarts or when the Reset button is pressed, we call it
Warm Booting or Soft Booting.

Data and Information

Data: It is the term used for raw facts and figures. For example- 134, +, 9, ‘Raju’, ‘C’ is data. 

Information: Data represented in a useful and meaningful form is information. 

In simple words, we can say that data is the raw material that is processed to give meaningful, ordered, or structured information. For example- Raju is 9 years old. This conversion of data to information is called data processing.

Functional Components of a Computer

The computer is a combination of hardware and software. Hardware is the physical component of a computer that can physically touch and see like Motherboard, Memory devices, Monitor, Keyboard, etc. while the software is the set of programs or instructions that enables computers to do some specific tasks. Both hardware and software together make the computer system functional. Computer Works on the basis of Input - Process - Output.

Input Unit

The input unit consists of input devices that are attached to the computer. These devices take input or our commands to the CPU and convert them into binary language that the computer understands. Some of the common input devices are Keyboard, Mouse, Bar code reader, lightpen, joystick, scanner, Digital Camera, etc.

Central Processing Unit (CPU)

The Control Unit (CU) and the Arithmetic Logic Unit (ALU) of a system are jointly known as the Central Process Unit. The CPU is the brain of any computer system. As the CPU is located on a small chip, it is also called the microprocessor. It is used to perform all types of calculations. The CPU has three main components which are responsible for different functions -

1. Arithmetic Logic Unit (ALU)
2. Control Unit (CU)
3. Memory Unit (MU) or Register

1. ALU - This part performs Arithmetic calculation like(+,-,*,/,%) and logical calculation like comparison (<,>,<=,>=,==,!=).

2. CU - This part responsible to manage all input and output processes of the computer.

3. MU - The data and Instruction that are entered into the computer system through input units have to be stored inside the computer before execution starts. Also, the results produced after processing must be kept somewhere inside the computer before being passed on to the output unit. It provides space for storing Instruction and data, space for Intermediate results, and space for the final result.

Output Unit

The output unit consists of output devices that are attached to the computer. It converts the binary data coming from CPU to human-understandable form. The common output devices are monitor, printer, plotter, speakers, etc.

Memory

Memory attached to the CPU is used for the storage of data and instructions and is called internal memory. During processing, it is the internal memory that holds the data. The internal memory is divided into many storage locations, each of which can store data or instructions. Each memory location is of the same size and has an address. With the help of the address, the computer can find any data easily without having to search the entire memory. The internal memory is also called the Primary memory or Main memory. When the task is performed, the CU makes the space available for storing data and instructions, thereafter the memory is cleared and the memory space is then available for the next task. The time of access of data is independent of its location in memory, therefore this memory is also called Random Access Memory (RAM). Primary memory is volatile in nature. That means when the power is switched off, the data stored in this memory is permanently erased. That is why secondary memory is needed to store data and information permanently for later use. Some of the examples of secondary storage devices are hard disk, compact disks, pen drives, etc. 

Interconnection between Functional Components 

Generally in microcomputers, a common bus architecture is used. Input unit, processing unit, an output unit, and memory all devices communicate with each other through a common bus. A bus is a transmission path (set of conducting wires) over which data or information is passed from one component to another in the form of electric signals. The bus can be of three types – Address Bus, Data Bus, and Control Bus.

The address bus carries the address location of the data or instruction. The data bus carries data from one component to another and the control bus carries the control signals. 

 First Generation (1942-1955)

The first generation computers were very large in size and occupying more space. They used Vacuum tubes as basic electronic components. These computers were the fastest calculating machines in those days. ENIAC was the first electronic computer. It was developed by a team headed by professors J. Presper Eckert and Jhon Mauchly. The ENIAC used thousands of Vacuum tubes. FORTRAN is a high-level language developed by IBM in This generation.

Example:  ENIAC ( Electrical numerical integrator and calculator ), EDVAC ( Electronic discrete variable automatic computer ), EDSAC ( Electronic delay storage automatic computer ), UNIVAC (Universal Automatic Computer).

 

Vacuum Tube

Features:

• Used Vacuum tubes.
• Based on Machine level and Assembly level languages.
• Memory was made of Magnetic drums.

Disadvantages:

• Large in size Occupied More space.
• Consume more power and required regular maintenance.
• Required air conditioning because of heat generated by Vacuum tubes.
• High cost.
• Very difficult to operate.
• Work very slow.
• Can't Move one place to another because they were very heavy in size.

Second Generation(1955-1964) 

The second-generation computer used a device called 'Transistor' in the place of 'Vacuum tube'. In 1947 three scientists, Jhon Bardeen, William Shockley, and Walter Brattain working at AT and T's Bell Labs invented Transistor. This transistor is a smaller device, which is more reliable than the vacuum tube. It consumed less power and emitted less heat. During this period, the first operating system was developed to communicate with computers.

Transistor

Example: UNIVAC 1108, IBM 1620, IBM-1401

Features:

• Used Transistors.
• Required less power to Run.
• Reduced Size. 
• Faster than 1st generation computers.
• Able to store some Data.
• Magnetic core memory used as Internal memory. 

Disadvantages:

Required air conditioning like the first generation of computers because they produced some amount of heat.

Third Generation(1964-1970)

The third generation computer used I.C (integrated circuits) in the place of 'Transistor'.This generation of computers was less expensive, smaller, faster, and accurate than second-generation computers. This generation rises mini computers. The first mini computer was PDP-8 which was big as a refrigerator.

Example: PDP, IBM 360, ICL

integrated circuit

Features:-

• Used Integrated Circuits.
• Faster, Smaller, and Reliable as compared to 1st and 2nd Generation. 
• Store large amounts of data as compared to the 2nd Generation.
• Used less Electricity.
• Less cost.

Fourth Generation(1971-Present)

In 1970 Ted Hoff developed a small chip at intel corporation. This small chip contains all CPU circuits of a computer. This chip named Intel 4004 and given a technical name as the microprocessor. Computers having microprocessors were called microcomputers.

Fourth-generation computers use semiconductor internal memory and new types of Softwares which make computers more efficient, reliable, and speedier.

Example: IBM-4300, Apple ii

Microprocessor

Features:-

• Used Microprocessor.
• They are cheaper and faster as compared to the 3rd generation computer.
• Easy to use and maintain.
• Used language C, C++ , java etc.
• High storage capacity.
• Used for general purpose and commercial purposes.

Fifth Generation(Present-Future)

Computers can not take decisions, but scientists are working to produce intelligent computers which can take decisions of their own, which can think like humans. Artificial intelligence is being built into computers.

 Abacus

Abacus was discovered by the Mesopotamians in around 3000 BC. An abacus consisted
of beads on movable rods divided into two parts. The addition and multiplication of
numbers were done by using an abacus. Today Abacus is used for young children to learn calculations.

Abacus

Napier’s Logs and Bones  

The idea of a logarithm was developed by John Napier in 1617. He invents a set of
numbering rods known as Napier’s Bones through which both multiplication and
division could be performed. These were numbered rods that could perform
multiplication of any number by a number in the range of 2-9. 

Napier’s Logs and Bones

Pascaline

Blaise Pascal, a French mathematician invented the adding machine in 1642 that was made up of gears and was used for adding numbers quickly. This machine was also called Pascaline and was capable of addition and subtraction along with carry-transfer capability. It worked on the clock work mechanism principle.

Pascaline

Leibnitz’s Calculator

In 1673 Gottfried Leibnitz, a German mathematician extended the capabilities of the adding machine invented by Pascal to perform multiplication and division as well. 

Jacquard’s Loom

In order to make the cotton-weaving process automatic, Joseph Jacquard devised punch cards and used them to control looms in 1801. The entire operation was under a program’s control. Through this historic invention, the concept of storing and retrieving information started.  

Difference Engine and Analytical Engine

Charles Babbage, an English mathematician developed a machine called Difference Engine in 1822 which could calculate various mathematical functions, do a polynomial evaluation, and could also solve differential equations.  

Difference engine

Thereafter in 1833, he designed the Analytical Engine which later on proved to be the basis of modern computer. This machine could perform all four arithmetic
operations as well as comparison. It included the concept of the central processor, memory storage, and input-output devices. Even the stored information could be modified.

Analytical Engine  

Both these great inventions earned him the title of ‘Father of Modern Computers’.  

Mark 1

In 1944 Prof Howard Aiken in collaboration with IBM constructed an electromechanical computer named Mark 1 which could multiply two 10 digit numbers in 5 seconds. This machine was based on the concept of Babbage’s Analytical engine.

In 1945, Dr. John Von Neumann proposed the concept of a stored-program computer. As per this concept, the program and data could be stored in the same memory unit. 

What is Computer

The computer is derived from the word 'compute' which means to calculate. A computer is an advanced electronic device/machine that takes data from the user and processes these data and gives the result (output). It can process both numerical and non-numerical (arithmetic and logical) calculations. It can process millions of instructions in a few seconds and at the same time with high accuracy.

Strengths of computer

Nowadays computers are being used in almost every field because of its strengths which are as follows:-

1. Speed: Computer works at a very high speed and completes the tasks within a few seconds.
2. Automation: Computer can work automatically without any interruption for example- Calculators can calculate automatically.
3. Accuracy: Computers are accurate. They do not make mistakes in calculations.
4. High storage capacity: Computers can store large data in its storage device. You can store almost any type of data such as movies, sounds, documents, etc.
5. Versatility: A computer can perform various types of jobs like calculations, railway reservations, Airlines, and much more.
6. Diligence: Computers can work continuously without any weakness, tiredness, and boredom.

Limitations of computer

1. No decision ability: Computers can not take decisions. It can work only according to the order given by the operator.
2. No emotions and feelings: Computers are far away from emotions, they can't have feelings and emotions.
3. Need electricity: A computer is an electronic machine it can't work without electricity.
4. Unable to self-protection: No matter how powerful a computer is but the truth is that computer can not protect itself in any way.