Classification of Computers

Classification of Computers

Based on the nature of data handled by a computers are classified into three types

1)Digital Computers 2)Analog Computers 3)Hybrid Computers

Digital Computers

A digital computer is a computer which can store and process data in the form of 0 and 1(Bit).It is based on the principle of counting.Digital computers are more accurate and faster.Desktop PC is an example of digital computer.

Analog Computers

An analog computer is a computer that operates on data in the form of continuous physical quantity( Such type of data includes temperature, pressure, speed weight, voltage, depth etc).It is based on the principle of measurement.Analog computers are used for scientific and engineering purpose.The main characteristic of analog computer is that they are very fast in operations as all calculations are performed in parallel mode.

Hybrid Computer

A hybrid computer is a combination of both digital and analog computers.They use analog technology for computation purpose and digital technology for storage.They are used in scientific and industrial purpose.

                                                          OR

Hybrid computers are computers that exhibit features of analog computers and digital computers.  A hybrid computer is one which combines the analog & digital capabilities in the same computer system. The hybrid computers help the user to exploit the machine's ability to process both continuous and discrete data.

Difference between digital and analog computers

The main difference between digital and analog computers are

Digital Computers	Analog Computers
It is based on the principle of counting.	It is based on the principle of measurement.
It can store and process data in the form of 0 and 1.( Digital computers Work on discrete values) OR Digital computers handle data in a discrete (noncontin- uous) form.	It can handle continuous data(values).
Digital computers are more reliable	Analog computers are less reliable
Digital computers are simple to operate.	Analog computers are difficult to operate

Classification of Computers according to functionality

Based on physical size , performance and area of application, computers are classified into four categories namely Micro computers,Mini computers,Mainframe computers and Super computers.

Micro Computers

A microcomputer is a computer with a central processing unit (CPU) as a microprocessor. Designed for individual use, a microcomputer is smaller than a mainframe or a minicomputer. 

A micro computer is a small,low cost digital computer whose cpu is a microprocessor.It is the smallest computer.Micro computers includes desktop PC,Laptop,PDA(Personal Digital Assistance) etc.

Mini Computers

A mini computer is also called mid-range computers. A minicomputer is a computer which has all the features of a large size computer, but its size is smaller than those. A minicomputer lies between the mainframe and the microcomputer.  Minicomputers are used for scientific and engineering computations, business-transaction processing, file handling, and database management.

Mainframe Computers

Mainframe computers are computers used primarily by large organizations for critical applications; bulk data processing, such as census, industry and consumer statistics, enterprise resource planning; and transaction processing. Mainframe computers have grater computing capacities than minicomputers and Minicomputers . The mainframe computers are used in large organizations such as Banks, Airlines and Universities etc. 

Super Computers

Supercomputers, the world's largest and fastest computers, are primarily used for complex scientific calculations. Performance of a supercomputer is measured in floating-point operations per second (FLOPS).

ANATOMY OF A COMPUTER

A computer mainly performs the following four functions.

1. Receive input – accept information from outside through various input devices like keyboard, mouse etc.
2. Process information – perform arithmetic or logical operations on the information.
3. Produce output – communicate information to the outside world through output devices like monitor, printer etc.
4. Store information – store the information in storage devices like hard disk, compact disk etc.

A computer has the following three main components.

1. Input/ Output Unit
2. Central Processing Unit
3. Memory Unit

a) Input/ Output Unit: Computer is a machine that processes the input data according to a given set of instructions and gives the output. The unit used for getting the data and instructions into the computer and displaying or printing output is known as input/ output unit. Keyboard is the main input device while the monitor is the main output device.

b) Central Processing Unit: Central processing Unit (CPU) is the main component or ‘brain’ of the computer which performs all the processing of input data. In micro computers, the CPU is built on a single chip or Integrated Circuit (IC) and is called Microprocessor. The CPU consists of the following distinct parts:

1. Arithmetic Logic Unit (ALU)
2. Control Unit (CU)
3. Registers
4. Buses
5. Clock

(i) Arithmetic Logic Unit: The arithmetic logic unit is responsible for all arithmetic operations like addition, subtraction, multiplication and divisions as well as logical operations such as less than, equal to and greater than.

(ii) Control Unit: The control unit is responsible for controlling the transfer of data and instructions among other units of a computer. It is considered as the ‘Central Nervous System’ of computer as it manages and coordinates all the units of the computer. It obtains the instructions from the memory, interprets them and directs the operation of the computer.

(iii) Registers: Registers are small high speed circuits which are used to store data, instructions and memory addresses, when ALU performs arithmetic and logical operations. Depending on the processor’s capability, the number and type of registers vary from one CPU to another.

(iv) Buses: Data is stored as a unit of eight bits in a register. Each bit is transferred from one register to another by means of a separate wire. This group of eight wires which is used as a common way to transfer data between registers is known as a bus. Bus is a connection between two components to transmit signal between them. Bus is of three major types namely data bus, control bus and address bus.

(v) Clock: Clock is an important component of CPU which measures and allocates a fixed time slot for processing each and every micro-operation. CPU executes the instructions in synchronization with the clock pulse. The clock speed of CPU is measured in terms of Mega Hertz or millions of cycles per second. The clock speed of CPU varies from one model to another.

c) Memory Unit: Memory unit is used to store the data, instructions and information before, during and after the processing by ALU. It is actually a work area (physically a collection of integrated circuits) within the computer where the CPU stores the data and instructions. Memory is of two types:

1. Read Only Memory (ROM)
2. Random Access Memory (RAM)

(i) Read Only Memory: Read Only Memory is an essential component of the memory unit. The memory which has essential instructions is known as Read Only Memory. This memory is permanent and is not erased when the system is switched off. The memory capacity of ROM varies from 64 KB to 256 KB depending on the model of computer.

(ii) Random Access Memory: Random Access Memory is used to store data and instructions during the execution of programs. Contrary to ROM, RAM is temporary and is erased when the computer is switched off. RAM is a read/ write type of memory and thus can be read and written by the user. As it is possible to randomly use any location of this memory, it is known as random access memory. The memory capacity of RAM varies from 640 KB to several mega bytes with different models of computer.

Hardware and software are two broad categories of computer components. Hardware refers to physical component while software to the programs required to operate computers. 

  INPUT DEVICES

An input device is any machine that feeds data, information and instructions into a computer. We may classify input devices into the following two broad categories.

1. Basic input devices
2. Special input devices

Basic Input Devices: The input devices which are essential to operate a PC are called basic input devices. These devices are always required for basic input operations. These devices include keyboard and mouse. 

Special Input Devices: The input devices which are not essential to operate a PC are called special input devices. These devices are used for various special purposes and are generally required for basic input operations. These devices include Trackball, Light Pen, Touch Screen, Joystick, Digitizer, Scanner, Optical Mark Reader (OMR), Bar Code Reader (BCR), Optical Character Reader (OCR), Magnetic Ink Character Recognition (MICR) and Voice-Input Devices.

Keyboard

Keyboard is the most common input device used for manual data entry. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys. Keyboard has been standardized for use in all types of computers such as a PC, a workstation or a notebook computer. The keys on computer keyboards are classified as follows:

1. Letter Keys: These are the 26 letters of English alphabet arranged as in a typewriter.
2. Digit Keys: There are two sets of digit keys; one on the second row from the top of the keys just as in a typewriter and the other is a numeric key pad at the bottom right which allows quick entry of numbers with the fingers of one hand.
3. Special character keys: These are characters such as <, >, ?, /, {, }, [, ], (, ), ., “, @, #, $, %, &, *, etc
4. Non-printable control keys: These are used for backspacing, going to the next line, tabulation, moving the cursor up or down, insert, delete characters etc. There is also a space bar at the bottom for leaving a space.
5. Function keys: These are labeled F1, F2 up to F15 and when pressed invoke programs stored in the computer.

You can understand the function of each and every key actually by working on a PC. When any key is pressed, an electric signal is produced. This signal is detected by a keyboard encoder that sends a binary code corresponding to the key pressed to the CPU. There are many types of keyboards but 101 keys board is the most popular one.

Mouse

Mouse is a device that controls the movement of the cursor on the display screen. It is a small object you can roll along a hard, flat surface. Its name is derived from its shape which looks like a mouse. As you move the mouse, the pointer on the display screen moves in the same direction. Mice contain at least one button and sometimes as many as three which have different functions depending on what program is running. There are three basic types of mice. They are mechanical, opto mechanical and optical. Wireless mice are also being manufactured. They transmit the motion of the mouse to the computer wirelessly and is convenient to use. Recently touch panel displays are manufactured which do not need a mouse as a locator. An appropriate icon on the screen may be touched either by finger or a pointing device such as a ballpoint pen to invoke the corresponding program.

Trackball

Trackball is an input device which is mostly used in notebook or laptop computer instead of a mouse. This is a ball which is half inserted and moving fingers on the ball, pointer can be moved. Trackball is considered better than mouse because it requires little arm movement and less desktop space.

Light Pen:

Light pen is a pointing device which is similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube. When the tip of a light pen is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU.

Joystick

Joystick is a pointing device which is used to move cursor position on a monitor screen. Joystick is a stick having a spherical ball at its both lower and upper ends. The lower spherical ball moves in a socket. Joystick can be moved in all four directions. The function of joystick is similar to that of a mouse. It is mainly used in Computer Aided Designing (CAD) and playing computer games.

Digitizer:

Digitizer is an input device which converts analog information into digital form. Digitizer can convert a signal from the television or camera into a series of numbers that could be stored in a computer. They can be used by the computer to create a picture of whatever the camera had been pointed at. Digitizer is also known as Tablet or Graphics Tablet because it converts graphics and pictorial data into binary inputs. A graphic tablet as digitizer is used for doing fine works of drawing. 

Scanner:

Scanner works more like a photocopy machine. It is used when some information is available on a paper and it is to be transferred to the hard disk of the computer for further manipulation. Scanner captures images from the source which are then converted into the digital form that can be stored on the disc. These images can be edited before they are printed. 

Optical Mark Reader (OMR):

OMR is a special type of optical scanner used to recognize the type of mark made by pen or pencil. It is used where one out of a few alternatives is to be selected and marked. It is specially used for checking the answer sheets of examinations having multiple choice questions. 

Bar Code Reader (BCR):

BCR is an optical scanner used for reading bar-coded data (data in the form of light and dark lines) Bar coded data is generally used in labeling goods, numbering of books etc. Bar Code Reader scans a bar code image, converts it into an alphanumeric value which is then fed to the computer to which the Bar Code Reader is connected.

Optical Character Reader (OCR):

OCR is an optical scanner used to read a printed text. OCR scans text optically character by character, converts them into a machine readable code and stores the text on the system memory. It is used for reading of passenger tickets, computer printed bills of credit card companies and reading of ZIP codes in postal services. 

Magnetic Ink Character Reader (MICR):

MICR is generally used in banks because of a large number of cheques to be processed every day. The bank’s code number and cheque number are printed on the cheques with a special type of ink that contains particles of magnetic material that are machine readable. This reading process is called Magnetic Ink Character Recognition.

Voice-Input Devices:

Voice-input devices are the latest input devices that can recognize the human voice. Microphone is a voice input device to input sound which is then stored in digital form. It is used for various applications like adding sound to a multimedia presentation or for mixing music.

OUTPUT/DISPLAY DEVICES

 Output devices are hardware components which are used to display or print the processed information. Output devices include monitor (display screen), printer, plotter, speaker, computer output microfilm etc.

 2.5.1 Monitor

Monitor is commonly known as Visual Display Unit (VDU) and it is the main output device of a computer. It forms images from tiny dots, called pixels that are arranged in a rectangular form. The sharpness of the image depends upon the number of pixels.

There are different kinds of monitors depending upon the number of pixels. Depending upon the resolution monitors can be classified as follows:

1. CGA (Colour Graphics Adapter)
2. MDA (Monochrome Display Adapter)
3. HGA (Hercules Graphics Adapter)
4. EGA (Enhanced Graphics Adapter)
5. VGA (Video Graphics Adapter)
6. SVGA (Super Video Graphics Adapter)

Depending upon the colour of display, monitors can be classified as Monochrome (with single colour black/white display) and colour (with all colours display) monitors.

  Printer

Printer is the most important output device which is used to print information on paper.

There are two types of printers.

1. Impact Printers
2. Non-Impact Printers

  

a)  Impact Printers: The printers that print the characters by striking against the ribbon and onto the paper are called impact printers.

Impact printers are of two types

1. Character Printers
2. Line Printers

i)  Character Printers: These printers print one character at a time. These printers are of two types – Daisy Wheel Printers and Dot Matrix Printers.

Daisy Wheel Printers: These printers print the characters by a mechanism that uses a plastic or metal hub with spokes called daisy wheel.

Dot Matrix Printers: These printers print the characters by putting dots onto the paper.

ii)  Line Printers: These printers print one line at a time. Their printing speed is much more than character printers. They are of two types – Drum Printers and Chain Printers.

Drum Printers: These printers print the line by rotating drum having a ring of characters for each print position.

Chain Printers: These printers print the line by rotating chain having ring characters for each print position.

b) Non-Impact Printers: The printers that print the characters without striking against the ribbon and onto the paper are called Non-Impact Printers. These printers print a complete page at a time. Hence they are also called Page Printers.

Non-Impact Printers are of two types

1. Laser Printers
2.  Inkjet Printers

(i) Laser Printers: These printers look and work like photocopier. They are based on laser technology. In these printers, a laser beam is used to write the image on a paper. There are many models of laser printers depending upon the speed and number of dots printed.

(ii) Inkjet printers: These printers print the characters by spraying the paper with electrically charged ink. These printers give better quality than character printers but not better than laser printers. They have an option of using colour cartridges for multi-colour printing.

   Other Output Devices 

Plotter: Plotter is used to print high quality graphics and drawings. It is generally used for printing/drawing graphical images such as charts, drawings, maps etc. of engineering and scientific applications. Some important types of plotters are:

a) Flat Bed Plotters: These plotters print the graphical images by moving the pen on stationary flat surface material.

b) Drum Plotters: These plotters print graphical images by moving both the pen and the drum having paper.

c) Inkjet Plotters: These plotters use inkjet in place of pen. They are faster than flat bed plotters and can print multi-coloured large drawings.

Speaker: Speakers are popular output devices used with computer systems. They receive audio input from the computer’s sound card and produce audio output in the form of sound waves. Most computer speakers are active speakers i.e. they have an internal amplifier which allows you to increase the volume, or amplitude of the sound. Speakers usually come in pairs which allows them to produce stereo sound from two separate audio channels. 

Computer Output Microfilm: COM is a technique to produce output on a microfilm media. A microfilm is a continuous film strip that can store several thousands of document pages. A microfilm card is a 4x6 inch film sheet which can store several hundred pages. The process of producing microfilm or microfiche takes place on a special COM unit. The information recorded on the microfilm is read with the help of a microfilm viewing system.

2.6  STORAGE DEVICES 

Memory units are the internal storage areas of a computer. The term “memory” refers to data storage that comes in the form of chips and the word “storage” is used for memory that exists on tapes or disks. The term memory is usually used as a short form for physical memory which refers to the actual chips capable of holding data. Every computer comes with a certain amount of physical memory usually referred to as the main (primary) memory or the Random Access Memory (RAM). The term RAM refers to read and write memory, that is, you can both write data into RAM and read data from RAM. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost. Read-only memory (ROM) refers to computer memory on which data has been prerecorded. Once data has been written onto a ROM chip, it cannot be removed and can only be read. Unlike the main memory (RAM), ROM retains its contents even when the computer is turned off. Hence it is nonvolatile. Most personal computers contain a small amount of ROM that holds instructions for starting up the computer.

There are different storage devices which are known as secondary memory devices. These devices are helpful in storing data, information and software permanently and they can be retrieved whenever required. They are also useful in transferring data or programs from one computer to another. Many storage devices are used with micro computers. Some of the common storage devices are explained below.

Hard Disk: Hard disk is a magnetic disk on which you can store computer data. The term hard is used to distinguish it from a soft or floppy disk. Hard disks hold more data and are faster than floppy disks. Hard disk is fixed inside the computer and is not easily removable. 

Hard disk consists of one or more disk platters, an access mechanism and read/ write heads which are sealed in a case. Hard disk size depends upon the disk platter’s diameter. There are many different platter sizes (5½, 3½, 2½ inch etc.) The 3½ inch size platter is common with  PCs and 2½ inch with laptop/ portable computers.

There are different types of hard disks depending upon their storage capacities. Storage capacities of hard disks range from 10 MB to several GBs.

Floppy Disk: Floppy Disk (FD) is a storage device which is small, flexible and easily removable. It is made of plastic disk coated with magnetic material which is sealed inside a square plastic jacket. It is called “Floppy” because it is soft having flexible physical properly. Data can be written on or read from this floppy by a drive called Floppy Disk Drive (FDD) which is fixed inside the computer. 

There are different types of floppies depending upon their sizes and storage capacities. Floppies come in two basic sizes namely 5¼" and 3½". The storage capacity of floppies varies from 360 KB to 1.44 MB. The floppies can store data on both sides (double-sided floppies) or on single side (single-sided floppies) depending on the floppy drive Double sided floppy drives are most commonly used.

Compact Disk: Compact Disk (CD) is a storage device used to store data, information and software which can be read only and not be changed or erased. It is an optical read only memory made up of resin. Therefore it is actually called Compact Disk Read Only Memory (CD-ROM). The information is stored on CDs by using an expensive drive called CD-ROM drive. CD-ROM drives can be either internal or external.

 

A single CD-ROM has the storage capacity of 700 floppy disks, enough memory to store about 3,00,000 text pages. Compact disks are very popular storage devices for micro computers because a large number of software including multimedia, audio and graphics software are available on these disks. They can be store a large volume of data (upto 680 MB) which is almost the same as a storage capacity of a 640 MB hard disk.

WORM (Write-once Read-many) is a type of compact disk which can be recorded only once and not erased. It can store more data than a CD-ROM, generally measured in gigabytes.

Digital Versatile Disk: Digital versatile disk read only memory (DVD-ROM) is a read only digital versatile disk commonly used for storing large software applications. It is similar to compact disk read only memory (CD-ROM) but has a large capacity. A DVD-ROM stores around 4.38 GB of data whereas a CD-ROM usually stores 650 MB of data. A DVD-ROM permanently stores data files that cannot be changed, written over or erased. A personal computer with a DVD-ROM or a DVD-RAM drive is designed to read a DVD-ROM disk. Generally a DVD-ROM disk is not equipped to be used with a DVD drive connected to a home theatre system or television. But many DVD-ROM drives can generally read a DVD movie disk. 

Compared to a CD-ROM, a DVD-ROM has the same 5 inch diameter and 1.2 millimeter thickness. But because a DVD-ROM uses a shorter wave length laser with tighter compacted pits, the disk capacity is increased. The smallest DVD-ROM can store approximately 7 times more data than a CD-ROM.

Pen Drive: Pen drive is a portable device which allows user to transfer data (text, images, videos etc) to and from computer quickly. Users can easily read and write the data in the pen drive by plugging it into USB port on the computer. Pen drives are quite compact and fit easily into the pocket. They run without battery and draw power from the USB connection itself. Both floppy disks and compact disks are now being gradually replaced by pen drive as preferred means of data storage. It offers mass data transfer and storage capability and at a much faster rate.

 

Storage capacity of Pen Drive can vary from few megabytes to over 100 megabytes. Pen Drive consists of an electronic circuit board and a USB connection that connects the drive to the computer. It is a memory chip which holds the data. Most Pen Drives are covered with plastic, metal or rubber casing for insulation. They are robust and scratch free thus ensuring maximum security for the data as compared to other traditional means of data storage.

Types of Computer- On the basic of working Principal

On the basis of working Principle the computer can be classified into: 
1. Analog computer
2. Digital computer
3. Hybrid computer


» Analog computer 
Analog computer operates on inputs of continuously varying electrical voltage. It measures the input rather than counting. The name that is derived from the Greek word 'analog' denotes that the computer functions by establishing similarities between two quantities that are usually expressed as voltages or currents. Analog computers are powerful tools to solve differential equations. They are mainly used in scientific design and production environments. Each one has to be constructed to do a specific job and will respond very quickly to changes in the measured inputs. 

» Digital Computer 
A digital computer operates essentially by counting. All quantities are expressed as discrete digits or numbers and computations are done with numerical digits. Mathematical expressions are represented as binary digits (0 and 1) and all operations are done using these binary digits at a very high rate. The digital computer basically knows addition. Remaining operations, like multiplication and division, are first converted -into addition and then calculated. Digital computer is much faster than analog computer and the computations are far more accurate. They come in various sizes starting from pocket size to the large systems occupying big rooms. Most of the computers available today are digital. 

» Hybrid Computer 
Hybrid computer combines features of both analog and digital computers. In this computer, some calculations are done in the analog portion of the computer and some are done in the digital portion of it. In a hospital, for example, analog devices may measure patient's heart function, temperature and other vital signs. These measurements may then be converted into numbers and supplied to a digital component in the system. This component is used to monitor the patient's vital signs and to send an immediate signal to the nurse's station if any abnormal readings are detected. 

Types of Computer- On the basic of size

On the basis of size the computer can be classified into: 
1. Micro Computer
2. Mini Computer
3. Mainframe Computer
4. Super computer
5. Workstations


» Micro Computer 
Microcomputer is at the lowest end of the computer range in terms of speed and storage capacity. Its CPU is a microprocessor. The first microcomputers were built of 8-bit microprocessor chips. The most common application of personal computers (PC) is in this category. The PC supports a number of input and output devices.
Microcomputers include (a) portable computers and (b) desktop computers.
(a) Portable Computer
Portable computer is a very small, easy to use microcomputer. The users can carry it wherever they go. This group includes personal digital assistant, pen-based computer, hand-held computer, notebook computer and laptop computer.
(a) Personal Computer or Desktop Computer
Personal computer is a microprocessor based, single user computer. The peripherals for personal computer include a keyboard and a mouse as input devices, monitor to display information and a hard disk for storage.

» Mini Computer 
Minicomputer is a medium sized computer that is costlier and more powerful than a microcomputer. It is in fact a scaled down version of mainframe computer. This can support up to a few hundred users at a time with multi-terminal, time-sharing system. They are mainly used as departmental computers in large and medium-sized organisations. They are also used in government departments, universities and R and D establishments. 

» Mainframe Computer 
The earliest computers were called mainframes due to their size. The term is still used for the large computers of today. They have large storage capacities, very high speed of processing (compared to micros and minis) and can support a large number of terminals (Many hundreds to thousands) for use by a variety of users simultaneously. They are kept in air-conditioned environment in a special computer room. They are used by big companies, banks, government departments, etc. as their main computer. 

» Super computer 
It is the fastest and the most expensive computer. This has extremely large storage capacities and computing speeds that are at least ten times faster than that of other computers. It can perform hundreds of millions of instructions per second. The super computer is used for specialised applications such as large-scale numerical problems in scientific and engineering disciplines. These include applications in electronics, petroleum engineering, weather forecasting, medicine and nuclear energy research. 

» Workstations 
Workstation is a powerful computer which in terms of power is between personal computer and minicomputer. It has high resolution graphics monitor, large RAM and secondary storage. Although it is a standalone system, usually it forms part of a network and it uses Unix or Windows NT as operating system. Workstations are used for specialised applications such as desktop publishing, software development and engineering designs. 

Types of Computer- On the basic of purpose of use

On the basis of purpose of use the computer can be classified into: 
1. Special Purpose Computer
2. General Purpose Computer


» Special Purpose Computer 
Special purpose computer is tailor-made solely to cater to the requirements of a particular task or application, for example, weather forecasting. It incorporates the instructions needed into the design of internal storage so that it can perform the given task on a simple command. It, therefore, does not possess unnecessary options, and costs less.

» General Purpose Computer 
The general-purpose computer is designed to meet the needs of many different applications. The instructions needed to perform a particular task are not wired permanently into the internal memory. When one job is over, instructions for another job can be loaded into the internal memory for processing. Thus, a general-purpose machine can be used to prepare paybills, manage inventories, print sales reports, do scientific calculations and so on. 

First Generation of mordern computer (1946 - 1954)

The period of first generation was 1946 - 1954. Computers of first generation used vacuum tubes as the basic components for memory and circuitry for Central Processing Unit.The first electronic computer, ENIAC (Electronic Numerical Integrator and calculator) was developed in 1947 at the University of Pennsylvania, USA. This machine had vacuum tubes as switching devices. Von Neumann introduced the concept of stored program by around the same time and the first digital computer using program, EDSAC (Electronic Delay Storage Automatic Calculator), was announced in 1949.
They were very large in size, consumed lot of power dnd emitted too much of heat. They required to be housed in large air-conditioned rooms.
During this period, computer programming was mainly done in machine language. The user had to be both an electronics expert and a programmer to use the computer for any task. 

Advantages of First Generatin of Computer:
» These computers fast and could calculate data in millisecond.
» Vacuum tubes were the only electronic component available during those days.
» Vacuum tube technology made possible to make electronic digital computers.
» Easily available and inexpensive.
» Tactile sensitivity is preserved.
» Color-coded for easier and faster identification of readings.


Disadvantages of First Generatin of Computer:
» The computers were very large in size.
» They consumed a large amount of energy.
» They heated very soon due to thousands of vacuum tubes.
» They were not very reliable.
» Air conditioning was required.
» Constant maintenance was required.
» Non-portable.
» Costly commercial production.
» Costly commercial production.
» Limited commercial use.
» Very slow speed.
» Limited programming capabilities.
» Used machine language only.
» Used magnetic drums which provide very less data storage.


Example of First Generation of Computer:

1. ENIAC (1946)
2. EDSAC (1949)
3. EDVAC (1950)
4. UNIVAC-1 (1951)

Second Generation of mordern computer (1955 - 1964)

The period of second generation was 1959-1965. In second generation of computer transistors were used. The transistors were highly reliable and easier to handle and maintain than the vacuum tubes. They required much less power. These transistors replaced vacuum tubes in computers during this period. The magnetic cores were used to construct large random access memories. Magnetic disk storage was also developed during this period.
Commercial applications rapidly developed during this period and dominated computer use by mid 1960s. This period also witnessed development of high level languages (like FORTRAN, COBOL, ALGOL, and SNOWBOL) and operating systems. The computers used multiprogramming and batch processing operating system.