Chapter 1

Introduction

A computer is an electronic device that can perform a variety of operations according to a set of instructions called programs. It is derived from ‘abacus’, which was  invented by Chinese. In earlier days computers were mainly used for computing. They were developed on mechanical devices. Now it has changed from mechanical to electronic.

History

The first (mechanical computer) called ‘Pascaline’ was developed by “Blasie Pascal” in “1642”. But it has no memory.

After this invention, ‘Joseph Jacquard’ invented ‘punched card’, by the end of mechanical revolution. This device has memory and was used for controlling looms. This leads to laid foundation for a method of storing and retrieving information.

During ‘1822-33’ ‘Charles Babbage’ invented the modern computer viz ‘difference engine’ (1822) and the ‘analytical engine’ (1833). He was named as the father of computer. This device has the facility to ‘store data’ and can do ‘arithmetic calculation’.

In ‘1890’, ‘Dr.Herman Hollerith’ has developed a census machine. This was developed for processing census data in America. So it was called ‘census machine’. It helps to process the census data with less time.

‘Dr.Hollerith’, invented “Tabulating Machine Company”, which later merged with other companies to form “International Business Machine (IBM)”.

In 1940s, the computing machines changed from mechanical to electro mechanical and then to electronic. The first digital computer ‘Harward Mark- I’ was developed by “Howard Aiken” in Harward University in 1944. It could perform its operations as per the programmed instructions.

Generation of Computers

1. First Generation (1949-1955):

            The first generation computers used (thermionic values) vacuum tubes and machine language was used for giving instructions. It was very large in size and generated immense heat. The programming was also very difficult. Consume huge electricity. Require bid a/c rooms.

Some Popular Computers:

a. ENIAC (Electronic Numerical Integrator and Calculator): First electronic computer was developed in 1946 by a team Professors lead by Prof.Eckert and Mannchly at Pennsylvania in USA. It has a very small memory. It could perform 5000 additions or 350 multiplications per second. It contains 18000 vacuum tubes, 70000 resistors, 10000 capacitors and 60000 switches. It is weighted 27 thonnes,30 meters length, 3 meters width and 1 meter height.

b. EDVAC (Electronic Discrete variable Automatic Computer): Binary arithmetic was used in this computer. Speed was considerably large in this type, was invented in 1950.

c. EDSAC (Electronic Delay Storage Automatic Computer): This computer was built by ‘Prof.M.V.Wilkes’ at Cambridge University in 1949. Merely delayed lines was used for storage.

d. GNIVAC- I: Commercial production of computers was started in 1950s. it was one such computer built by Univac division of Remington Rand and delivered in 1951.

Important Limitations of first generation computers:

1. Slow operating speed

2. Limited computing capacity

3. High power consumption

4. Short life span

5. Large space requirement

6. Limited Programming capabilities

7. Huge emission of heat

8. Small memory

9. High cost, etc.

2. Second Generation (1956-65):

Second generation computers were used transistors, which is              highly reliable than vacuum tubes. Transistors were developed by USA scientists viz: Bardeen,     Brattain and Shockley in 1946. Transistors have long life, high reliability, low cost, high speed and high storage capacity.

Second Generation computers used High Level Languages (HLL) like CUBOL, FORTRAN etc. Commercial applications rapidly developed during this period and more than 80% of these computers were used in business and industries.

Key Features of second generation computers:

1. Transistors replaced by vacuum tubes.

2. Small in size.

3. Low power consumption.

4. Generate low heat.

5. More reliable and faster.

6. Core memory developed.

7. Disks and magnetic tapes used.

8. First operating system developed.

9. Programming in both machine language and assembly language.

3.  Third Generation (1966-1975):

            During this period transistors were replaced by ICs (Integrated circuit chips). It was invented by Jack Kilby in 1958. In an I C, several transistors, resistors and capacitors are integrated with other electronic components and sealed up in a small package. The I C, have larger speed, large storage space and considerably lower price.

During its initial stage there were Small Scale Integrated (SSI) circuits with only 10 transistors per chip. The technology developed to Medium Scale Integrated (MSI) circuits which were developed with 100 transistors per chip later during 1970s.  Large Scale Integration (LIC) contains thousands of components in one chip. Soon after, Very Large Scale Integration (VLSI) with millions of transistors was invented. This leads to the invention of micro computers and as a result it leads a drastic change in this field.

Eg:  

1. IBM 360 series.             2. IBM-370/168.         3. ICL-2900.

4. Honey well-316.                       5. GNIVAC etc.

Key Features of third generation computers:

1. Developed ICS.

2. Computer smaller, faster and reliable.

3. Low power consumption.

4. High-level language appeared.

5. Parallel programming.

4. Fourth Generation computers (1976-80):

The advent of ‘Micro processors’ (chips) and ‘micro computers’ are the major development during this generation. This was due to the contribution of VLSI (Very Large Scale Integration). It leads to the emergence of extremely powerful personal computers. Faster processing and increased memory helped in the development of more powerful operating system.

The first personal computer (PC) was developed in the late 1970s by ‘Apple Corporation’ of USA. The first pocket computer developed in Japan was sold in 1980, named ‘Sharp P.C-1211’.

Key Features

1.      Integrated circuits.

2.      Micro computer series such as IBM and Apple developed.

3.      Developed portable pocket computers.

4.      Different types of secondary memory with high storage capacity.

5.      Fast access and processing developed.

Various Processors: (Micro Processors)

a. Silicon chip: The invention of silicon chip reduced the size of computer. In this chip a number of transactions were integrated to form this processor. It has a small size of “0.5 in square”.

b. Super chips: The researchers in semi conductors were developed super chips. In this processors millions of transistors were packed into a finger nail sized chips. Intel’s various versions can be seen.

c. Celeron chip: Inter processor also launched a chipset to work with the Celeron. It performs more functions and has only a lesser cost. It finally leads to reduce this cost of ‘Motherboard’, the main component in the ‘CPU’

d.: It is another processor which was developed by another developer, it is cheaper than inter processor and at the same time has a good performance. It leads to gain a good place in the market.

5. Fifth Generation computers (from 1980):

            Artificial intelligence was the main contribution of fifth generation computers. Conventional computers can process one instruction at a time. Now parallel processing is possible to process a verities of instructions at a time. It can blend voices, images and helps to assimilate and dissimilate large quantity of data from different sources, with the help of artificial intelligence and supportive mathematical models. The fifth generation computers can do more than trillion mathematical calculations per second. It is called terat lap (Greek word) which means teras (one trillion) flap (floating point operations per second)

Key features of fifth  generation computers:

1. Parallel processing: Many processors are grouped to functions one large group processor.

2. Super conductors: This is a conductor through which electricity can travel without any resistance, which results faster transfer of information between the components of a computer.

Important Parts of a Computer

Input device
		Primary memory
		Control unit
		ALU

Output device

1. Input Unit:

The Input unit is responsible for accepting input i.e., data and instructions from the user for processing. This work is accomplished with the help of input devices. There are several equipments that perform this function. They are:

a. Keyboard: 

            Keyboard is a typewriter like device which is used to type in the letters, digits, programs and commands. A keyboard contains a matrix of switches. Keyboards are used to enter data by typing it in manually. Each key when pressed sends a digital code to the computer that determines which key has been pressed. Most desktop and notebook computers come with a standard keyboard, which uses the QWERTY keyboard layout.

Advantages:               1. Reliable way of inputting text and numbers.

                                    2. Available in variety formats.

Disadvantages:           1. Not suitable for pictures, diagrams, voice, video etc.

                                    2. Very slow while accessing menu options.

                                    3. Not much useful for enlarging or changing sizes of windows.

b. Mouse and other pointing devices:

            The mouse is a pointing device used to point a cursor on a particular point in the monitor. A mouse generally has two or three buttons it may or may not have a ball. Mouse controls movement of pointer (mouse pointer) on screen. When a mouse moves on a flat surface, the cursor on the screen also moves in the direction of mouse’s movement. Now the optical mouse is widely used in the place of earlier version.  Te earlier model has a roller ball on the bottom, and moves when the user drags the mouse across a mouse pad.

c. Digital Pen:

            The Digital Pen works in conjunction with a flash drive (a portable electronic storage device) that connects to a port on a computer. The user can write with the pen on any conventional paper, and the writing is captured and then transmitted wirelessly and stored in the flash drive. When the flash drive is connected to a computer, one can use software to translate the writing into digital text.

d. Image input devices:

            Digital cameras, camcorders, and webcams are the most common devices for capturing pictures and video. Digital cameras and camcorders can be used to capture images in remote areas and later downloaded to a computer. Webcams are small cameras on top of the computer monitor or are built into the notebook computer. It helps in video conferencing, conduct classes or to call with video phones.

e. Sound input devices:

            A microphone is a device that helps to capture sound waves and transfer them to digital format on the computer. Close-talk microphones which are usually attached to a headset are useful in situations such as using speech- recognition software, videoconferencing, or making telephone calls. Handheld microphones are convenient for recording podcasts. Clip on microphones are useful when you are presenting at a meeting.

f. Joystick:

            Joysticks are often used for playing computer games such as flight simulators. They input directional data like mouse but work by switches being closed as the joystick is moved left or right and up or down. Mini finger-controlled joysticks can be used to control a laptop cursor.

g. Scanner

            Scanner is a device similar to a photocopier. A photocopier prints the given printed image on a paper, while a scanner creates an electronic form of the printed image, which can later be manipulated, changed and modified according to the requirements.

g. Other input devices:

            The Bar code scanners read bar codes. Bar codes are made up of bars of different widths and spacing that convey alphabetic and numeric information about products or addresses. The bar code scanners are accurate, fast and inexpensive which has made it popular at supermarket checkout counters, where the billing employee uses them to read the bar code labels on cans, boxes and bags.

2. The Central Processing Unit (CPU)

            The Central Processing Unit (CPU) is responsible for carrying out the processing job. The CPU is the brain of the computer. It is where all the searching, sorting, calculating, and decision making takes place. The CPU is the control centre for a computer. It guides, directs and controls a computer’s performance.

Components of CPU

A CPU has two components:

1. Memory Unit

2. Arithmetic Logic Unit (ALU)

3. Control Unit(CU)

1. Memory Unit

Computer stores data in the memory unit in the form of binary numbers. A binary number is either a zero (0) or one (1) and is known as a bit which is the short form of binary digit. The memory unit has two sectors namely Primary Memory and Secondary Memory.

8 Bit = 1 Byte

1024 Bytes =1 KB

1024 KB= 1 MB

1024 MB= 1 GB

1024 GB = 1 TB

a. Primary Memory

            It is the main memory in a computer. It is also known as the internal memory which is the ‘Immediate Access Store(IAS)’ . The IAS holds the data and programs needed at that instant by CPU. There are two types of primary memory such as RAM and ROM.

(1)RAM (Random Access Memory)

            The internal memory read from and written to is called RAM. It is volatile i.e. not fixed. Its contents are lost when power is turned off. The computer has to execute various functions and for this purpose a large amount of data and information is to be stored and to retrieve as and when required. These information and instructions are stored in RAM in the main memory. When people talk about computer memory in connection with computer they usually mean the RAM.

Limitations of RAM

(i)Limited storage capacity

(ii)Volatile in nature

(2)ROM (Read Only Memory)

            In this memory, the information stored remains fixed and will never be lost when power is turned off. ROM can only be read and used, it cannot be changed. Hence it is called Read Only Memory (ROM). It generally contains a set of startup instructions that is what to do when a computer is turned on. This information is stored in the ROM chip at the time of manufacture. The system files are of these types which are necessary for booting the system. At present different types of ROM are available. They are PROM(Programmable ROM) , EPROM(Erasable PROM) , EEPROM(Electrically EPROM) .

Difference between RAM and ROM

RAM	ROM
1. Volatile	1. Permanent
2. Can be read and be changed	2. Can be read but cannot be changed.
3. It is mainly referred as memory of a computer.	3. No mention in this regard.
4. Both the system software and application software can be stored	4. Only system software
5. It remains blank at the time of manufacture	5. The software is loaded at the time of manufacture.

 Role of Primary Memory

1. To hold the commands of the program currently being processed

2. To hold the data required by the current program

3. To hold the intermediate processing result.

4. To hold the output that is ready to be transmitted to output device or to secondary storage.

3. Cache Memory

     The speed of processing is mainly based on the memory status. In various occasions the performance of the processors are very slow or limited due to the slow speed or small size of main memory. In order to balance this situation of slow operating speed, and extremely fast, small memory is used in between the CPU and Main Memory. This type of memory is called hi-speed buffer or cache memory. It is a hiding memory and is not addressable by the user of the computer. It is very expensive and is small in size.

b. Secondary Memory

            The secondary memory is mainly used to store data for a long period of time. Since the primary memory has only a limited storage space, secondary memory is necessary to store the data and information for future uses. For this purpose there are certain external devices, and this is used to store data for longer duration with larger capacities. On the basis of accessibility of data the external devices can be categorized into two. They are

(a) SAM (Sequential / Serial Access Memory): In SAM data can be accessed in the order it has been stored. Data in connection with results are generally stored in SAM.

Example: Magnetic Tape

(b)RAM (Random Access Memory): RAM also known as direct access memory, permits to access individual information immediately as and when required. It is a most widely used type of memory. 

Types of Secondary Storage Devices

            The secondary storage devices are either magnetic media or optical media. The magnetic media consists of hard disk; floppy disk etc and the optical media consist of CDs, ROMs etc

1. Magnetic Media

a. Hard Disk:

            Hard Disk is an important secondary storage device which is kept commonly in the computer. It is a thin steel platter with iron oxide coating. It is always rotating at a speed more than 3500rpm (rotations per minute), information is recorded on the surface of rotating disc by magnetic heads. These heads are mounted on access arms which help to read the data.

Advantages:

            1. Large storage capacity

            2. Stores and retrieves data much faster than a floppy disc or CD ROM.

            3. It is a permanent storage.

            4. Since it is fixed inside the computer there is no chance for loss or damage.

Disadvantages

            1. Slower than RAM

            2. Cannot be easily transferred from one form to another. 

b. Floppy Disk:

            Floppy Disc is one of the portable storage devices and at present it is rarely used. It enables to transfer small files from one computer to another and also to store information as back-up. A Floppy Disc is made of a flexible substance called Mylar. They have a magnetic surface which allows the recording of data. A standard Floppy Disc can store up to 1.44 MB of data which is approximately equivalent to 300 A4 pages of text. All discs are to be formatted before writing data on it. Formatting means marking and dividing the disc into tracts and sectors. The floppy disc is divided into many concentric circles called track. Each track is further sub-divided into smaller pie-shaped sections called sectors.

Advantages

            a. Portable, small and light weight.

            b. It is inexpensive.

            c. Useful for transferring data or files between computers.

            d. It is reusable.

Disadvantages

            a. Not very strong, easy to damage.

            b. Slow to access and retrieve data.

            c. Small storage capacity.

2. Optical Media

a. Compact Disc (CD):

            CDs are relatively cheap and have a storage capacity upto 700 MB. In the CD information is recorded in the spiral tract. A laser device is used to burn microscopic pits , in the reflective layer on the CD for recording  data. A CD can store text data, audio, video , photos etc. There are three main types of CDs.

(i)CD-ROM: This type of CD is used to store information and cannot be used to store data. Manufacturers use CD-ROMs to record information including text, audio or video on the CD for distribution.

Example: Software, Games, Encyclopedia, E-Books etc

(ii)CD-R (CD-Recordable): Data can be recorded only once on these disks. These CDs allow writing on one part of the disc one time and another part at the later time. However it can be done only once.

(iii)CD-RW (CD-Rewritable): It is an erasable disc and can write on multiple occasions. But the number is limited.

(b)Digital Versatile Disc (DVD):

                It is another optical device which looks like a CD, but is able to hold about 15 times than a CD. It can hold upto 20 GB of data. It is also called a super density disc and can hold up to 17 GB.DVDs also come in three varieties namely DVD-ROM, DVD-R,DVD-RW.