Basics of Information Technology PDF

# Chapter 1: Basics of Information Technology ## Overview We are living in the Information Age of a Global Village today. That means Information is the key factor in this era and it is rightly said that "Information is the most precious commodity of today's day-to-day business". Everything evolves...

# Chapter 1: Basics of Information Technology ## Overview We are living in the Information Age of a Global Village today. That means Information is the key factor in this era and it is rightly said that "Information is the most precious commodity of today's day-to-day business". Everything evolves around it whether it is education, medicine, history, geographical phenomena, sports, research or business. You name the system and Information is there to play a key role in its functionality and existence. Information can be defined as the facts and figures about anything i.e. The know-how about any object that exists and plays its role in any system. The system is any identified and known work that accepts data/information into itself, manipulates in the shape of certain output(s) and delivers so that it becomes useful and meaningful. And precisely, that is what is known as "Data processing" or "Computing", for which we need a computer to accomplish the task. Few years back, this accomplished task was available to the computer users/clients in a prescribed locality only. That locality could be his own office or organization. But with the advent of Communication technology, our globe has become virtually a one-community area i.e. Global Village. The organizations expanded to remote cities and countries and it was felt to make the data/information and the ultimate accomplished task available to them where-ever they are. There came communication technology to our rescue and a new term emerged i.e. "Information Technology" that can be precisely defined as: "Information Technology is the technology that merges computing with high- speed communication links carrying data in the form of text, sound, images, video etc", from place to place over this global village. For this purpose, the computer systems are networked in such a way that the data/information stored/processed on them is always available from anywhere, at any place, at any moment. Thus, the computer users are almost always sharing and exchanging their information in such a manner as if they are sitting in a drawing room face to face. So in short, Information Technology enables the heterogeneous types of industries and institutions to a phenomenon known as digital convergence. The digital convergence is the technological merger of various industries/enterprises through some electronic gadgets that exchange information between them. The industries are computers, electronics, telecommunications, and mass media etc. It has tremendous significance in modern scenario. It means that from a common electronic base, information can be communicated to any shape that the users are accustomed to see i.e. photographs, movies, audio, graphical shapes, text form, analog diagrams etc. ## Modern Scenario The modern impact of Information Technology has broadened the base of computing and communication through satellite, fiber-optic, mobile phone, fax machine, multi-media/hyper-media, e-commerce, m-commerce etc. Thus enhancing the implications of this shift from single isolated technologies to a unified digital convergence and enabling the computer users to experience a beautiful and fantastic scenario of computer utilization in the fields like: * Artificial Intelligence * Web-based Applications * E-commerce, M-commerce (Mobile Commerce) * Computer Animation * Multi-media, Hyper-media * Distributed Computing There are numerous fields of computer applications, but we need not to go into the details of all those as it is beyond the scope of this book. What we need to know here is that the Information Technology has brought about a revolution in our life style. We may call it the Computer Revolution, Information Revolution, Communications Revolution, Internet Revolution, Multi-media Revolution or whatsoever. So it is beyond any doubt that today, we are living in a society that is making use of "Information Highway" which is heading towards a real future "Global Village" of the human history. ## 1.1 Hardware and Software "A computer is a machine that can be programmed to accept data (input), process it into useful information (output), and store it away (in a secondary storage device) for safekeeping or later reuse". We have four words in this definition which are of prime importance in the whole computing process i.e. machine, program, input and output. By conventions, machine is called hardware, whereas a program is known as software in the discussion of computer science. Here, input and output devices are part of the machine that can now be called as a complete Computer system. So, to function, a computer system requires four main aspects of data handling i.e. input, processing, output and storage (figure 1.1). The hardware, responsible for these four areas, operates as described below: * **Input devices** accept data in a form that the computer can use, and then sends it to the processing unit. * **The processor (CPU)**, has the electronic circuitry that manipulates input data into the form of useful information. The processor actually executes the instructions (Programs) in a logical sequence. * **Output devices** show us the processed data i.e. information, in the shape we want it. * **Storage** usually means secondary storage, which consists of secondary storage devices, such as hard disk, floppy diskettes, CDs etc. which can store data and programs outside the computer itself. These devices actually supplement main memory, which can hold data and programs only temporarily. **Figure 1.1: A generalized Computing Environment** (A diagram of a computer showing input, processing, output, and secondary storage) ## 1.1.1 Hardware Devices Following are the main hardware devices in any computer system: * Input Devices i.e. Keyboards, Mouse, Microphones etc. * Output Devices i.e. Printers, Speakers, Monitors etc. * Main Memory comprising of RAM and ROM * I/O Device i.e. Terminals, Touch Screen etc. * Secondary Memory i.e. Hard disk, Floppy disk, Compact disk, Tape etc. * Inter-connectors i.e. Cables, Ports, Buses etc. * Networking Devices i.e. Modem, Bridge, Router etc. ## 1.1.2 Software Classification Software can be classified into following main two categories: * System Software * Application Software ### System Software System software is used to control the usage and allocation of different hardware components and enables the other application programs to execute. For example, * Operating Systems * Utility Programs (Backup/Restore) * Drivers The system software may be a combination of many such programs. ### Application Software Application software is the software that has been developed to solve a specific problem or to provide audio, video, or multimedia entertainment to the users. It may be categorized as under: * Custom-built * Packaged #### Custom-built software This is the software that is designed and developed for a particular customer. The custom-built software is discussed in detail in the section 1.6 (Systems Development). #### Packaged software This software is the kind of off-the-shelf programs or components, developed for sale to the potential software developers/users for their use. The examples are: MS-Word, MS-Power point, Personal Oracle etc. few of these are discussed in the coming chapters. ## 1.2 Input and Output devices We need some, device(s) to enter the data into the computer (Input devices) and some device(s) to see the outcome (or processed information) of the computer (Output devices). Both discussed as below: ### 1.2.1 Input devices Sometimes, the data is entered directly to the computer and sometimes indirectly. In the first case, the data goes directly to the computer from the source and in the second case; we have to carry out some intermediate handling. In either case the task is to gather data to be processed by the computer. There are three general types of input hardware, namely: * Keyboards * Pointing devices * Source data-entry devices #### Keyboard The keyboard may look like a typewriter keypad to which some special keys have been added. The keys normally available on the keyboards are Numeric, Alphabetic, Function and additional Special-purpose keys. Figure 1.2 shows the complete layout of an extended keyboard on a personal computer. It has some additional keys between the main keypad and the numeric keys, and status lights in the upper-right corner. This standard keyboard is also called "QWERTY", which describes the beginning keys in the top row of alphabetic letters. **Figure 1.2: A 101-key "Enhanced" keyboard, showing the layout of the various key groups.** (A diagram of a keyboard, showing the different key groups) #### Function keys The function keys are an easy way to give certain commands to the computer. The particular software we use defines what each function key does. #### Main Keyboard The main keyboard includes the familiar keys found on a typewriter keypad, as well as some special command keys. The command keys have different uses/effects that depend on the software being used. Some of the most common uses are listed here: **101-Key "Enhanced" Keyboard Layout** extra buttons and keys are based on this layout. * **Esc** - The Escape key, is used in different ways by different programs; often it allows to "escape" to the previous screen of the program. * **Tab** - The Tab key, is used to tab across the screen and set tab stops as on a typewriter. * **CapsLock** - When the CapsLock key is pressed, upper case letters are produced. Numbers and Symbols are not affected. The number or symbol shown on the bottom of a key is still produced. When the CapsLock is pressed, the status light under "CapsLock" lights up. * **Shift** - The Shift key is pressed in combination with other keys to produce upper case letters and the upper symbols shown on the keys. * **Ctrl** - The Control key is pressed in combination with other keys to initiate commands as specified by the software. * **Alt** - The Alternate key is also used in combination with other keys to initiate commands. * **Backspace** - The Backspace is used to delete a character to the left of the cursor, moving the cursor back one position. The cursor is the flashing indicator on the screen that shows where the next character will be inserted. * **Enter** - The Enter key moves the cursor to the beginning of the next line. For instance it is used at the end of a paragraph. * **Numeric Keys** - The numeric keys serve one of the two purposes, depending on the status of the Num Lock key. When the computer is in the Num Lock mode, these keys can be used to enter numeric data and mathematical symbols (/ for "divided by", for "multiplied by", for "subtraction" and + for "addition"). In the Num Lock mode, the status light under "Num Lock" key lights up. When the computer is not in the Num Lock mode, the numeric keys can be used to move the cursor and perform other functions, as given below. * 1 - End - In some programs, the End key moves the cursor to the bottom- right corner of the screen. * 2 - ↓ - This key moves the cursor down one line. * 3 - PgDn - The Page Down key advances one full screen while the cursor stays at the same place. * 4 - ← - This key moves the cursor one character to the left. * 5 - → - This key moves the cursor one character to the right. * 6 - Home - In some programs, the Home key moves the cursor to the top- left corner of the screen. * 7 - ↑ - This key moves the cursor one line up. * 8 - PgUp - The Page Up key backs up to the previous screen while the cursor stays at the same place. * 9 - Ins - The Insert key, when toggled off, causes keyed characters to override/affix with the existing characters. * 0 - Del - The Delete key deletes a character, space, or selected text. * **Extended keyboards** include additional keys that duplicate the cursor movement functions of the numeric keys. Users who enter a lot of numeric data can leave their computers in the Num Lock mode and use these additional keys to control the cursor. * **Arrow keys**, to the left of the numeric keys, move the cursor position, just as the numeric keys 2,4,6, and 8 do when they are not in the Num Lock mode. * **Just above the Arrow keys are six keys--- Insert, Delete, Home, End, Page Up, and Page Down --- which duplicate functions of the numeric keys 0, decimal point (Del), 7,1,9, and 3**. * **At the top of the keyboard, to the right of the function keys, are keys that perform additional tasks, as mentioned below**: * **Print Screen** - The Print Screen key causes the current screen display to be taken a copy of information or image on the screen. * **Scroll Lock** - The Scroll Lock key causes lines of text images - not the cursor - to move. When the computer is in the Scroll Lock mode, the status light under "Scroll Lock" lights up. * **Pause** - The Pause key causes the screen to pause when information is appearing on the screen too fast to read. #### Function Keys These keys are at the top of a computer keyboard labelled F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11 and F12. The functional keys are an easy way to give certain commands to the computer, which are usually operated by keyboard commands. They have different functions in different program. These functions are particularly important in an application program. #### Pointing devices Pointing devices control the position of the cursor or pointer on the screen. They include the following: * Mouse * Pointing Stick * Touch Screen * Digitizing/Graphic tablet * Trackball * Touch pad * Light pen * Pen-based system ##### Mouse A mouse is an input device that looks a little bit like a mouse. It has a ball on its underside that is rolled on a flat surface or mouse-pad. The rolling movement causes a corresponding cursor movement on the screen. It enables us to reposition the cursor (or pointer) on the screen where ever we want. It also has buttons on its top which communicate certain commands to the computer while pressed. In particular, button is often used to click on an icon (icon represents a computer activity or command) to invoke the command. ##### Trackball The trackball is a movable ball, on top of a stationary device, that is rotated with fingers or palm of the hand. Its popularity surged with the advent of laptop computers where traveling users found themselves without a flat surface to roll the traditional mouse. It looks like the mouse turned upside down and likewise, has additional buttons whose functions vary depending on the software. ##### Pointing Stick A pointing stick is a pointing device that looks like a pencil eraser protruding from the keyboard between the G, H, and B keys. We move the pointing stick with our forefinger while using the thumb to press buttons located in front of the space bar. Another device like a Pointing stick is the Joystick, It is a pointing device that consists of a vertical handle like a gearshift lever mounted on a base with one or two buttons. It is basically used in video games and in some computer-aided design systems. ##### Touch pad The touch pad is a small, flat surface over which we slide our finger, using the same movements as we would with a mouse. As we move the finger, the cursor follows the movement. We "click" by tapping the finger on the pad's surface or by pressing button positioned close by the pad. Touch pads are now common on the portable computers (laptops). ##### Touch Screen A touch screen is a video display screen that is sensitized to receive input from simply touching our fingers onto it. It is covered with a plastic layer, behind which are invisible beams of infrared light. We simply touch the provided buttons or menus and get the information on the display screen accordingly. ##### Light Pen The light pen is a light-sensitive stylus, or pen-like device, connected by a wire to the computer terminal. The user brings the pen to a desired point on the display screen and presses the pen button, which identifies that screen location to the computer. Engineers, graphic designers, and illustrators use light pens. ##### Digitizing/Graphic Tablet A digitizing tablet consists of a tablet connected by a wire to a stylus or puck. A stylus is a pen-like device with which the user "sketches" an image. A puck is a copying device with which the user copies an image, such as an architectural drawing or a civil engineering map. A puck looks a bit like a mouse but has different types of buttons and a clear plastic section extending from one end with crosshairs printed on it. The intersection of the crosshairs points to a location on the graphics tablet, which in turn is mapped to a specific location on the screen. Digitizing tablets are used primarily in design and engineering. When used with drawing and painting software, a digitizing tablet and stylus allow us to do shading and many other effects similar to those artists achieve with pencil, pen, or charcoal. Alternatively, when we use a puck, we can trace a drawing laid on the tablet, and a digitized copy is stored in the computer. ##### Pen-Based Systems In the next few years, students may be able to take notes in class without ink and paper, if pen-based computer systems are introduced. These computers use a pen-like stylus to allow people to enter handwriting and marks onto a computer screen rather than typing on a keyboard. This system connects an instructor's electronic "whiteboard" on the classroom wall with student's pen computers, so that the students could receive notes directly, without having to copy information word for word. "The idea is that the students should concentrate on the lecture listening only". ##### Source Data-Entry Devices These devices are used for direct data entry to the computer systems. Few of them are as under: * Bar-Code Reader * Mark- and character-recognition device * MICR (Magnetic-Ink Character Recognition) * OMR (Optical Mark-Recognition) * OCR (Optical Character-Recognition) * Magnetic-stripe cards * Smart cards * Fax machine * Imaging system * Audio/Video Devices * Audio-input device * Video-input device * Digital camera ###### Bar-Code Reader Bar codes are the vertical zebra-stripped marks we find on most of the manufactured products in the market. This bar-code system is also called the "Universal Product Code". These are read by bar-code readers, photoelectric scanners that translate the bar-code symbols into digital code, which is then fed to the computers for further processing. ###### MICR It is a method of machine-reading characters made of magnetized particles. MICR characters, which are printed with magnetized ink, are read by MICR equipment, producing a digitized signal, which goes to the computer as data for further processing. ###### OMR Optical recognition systems use a light beam to scan input data to convert it into electrical/digital signals, which are then sent to the computer for processing. The most well known example is the OMR technology used to read the SAT and GRE test marks. ###### OCR It uses a device that reads preprinted characters in a particular font and converts them to digital code. The common examples are some utility bills and price tags in the department stores. ###### Magnetic-strip cards A magnetic-strip card has a strip of magnetically encoded data on its back. They are used for personal identification during driving, in the stores, at public places etc. ###### Smart cards It looks like a credit card but a microprocessor and memory chip have been added additionally. When inserted into a reader, it exchanges data with the corresponding information on a central computer. It can store some basic information also. A Mobile-SIM card and an ATM card are good examples of this type. ###### Fax Machine The fax or facsimile transmission machine scans an image and sends it as electrical signals over telephone lines to a receiving fax machine, which re-creates the image on paper. We have two types of fax machines i.e. dedicated fax machines and fax modems. Dedicated fax machines are the normal fax machines whereas, the fax modem is a circuit board inside the system unit. It has a capability to send signals directly to someone else's fax machine or computer fax modem, from computer to computer. ###### Imaging System Image scanner (graphic scanner) converts text, drawings, and photographs into digital form and stores it to the computer system for further processing. The system scans each image (color or black and white) with light and breaks the image into light and dark dots or color dots, which are then converted to digital form. This is also called raster graphics, which refers to the technique of representing a graphic image as a matrix of dots. ###### Audio/ Video Input Devices * **Audio-Input device:** An audio-input device records analog sound and translate it for digital storage and processing. The principal use of audio-input devices is to provide digital input for multimedia computers, which incorporate text, graphics, sound, video and animation in a single digital presentation. Sound (analog form) goes through a special circuit board called an audio board, which converts analog sound to digital form and stores it for further processing and/or plays it back. Microphone is mostly used as an audio-input device. * **Video-Input device:** Films and video images from VCR or camcorder are converted to digital form with the help of a special digitizing card (called video-capture card). It has two types: * **Frame-grabber video card:** It can capture and digitize only a single frame at a time. * **Full-motion video card:** Also known as adapters, can convert analog to digital signals at the rate of up to 30 frames per second, giving the effect of a continuously flowing motion picture. * **Digital Camera:** A digital camera uses a light-sensitive processor chip to capture photographic images in digital form on a small diskette inserted in the camera or on flash-memory chips. The digital form is then uploaded to the computer for manipulation and printing out. ## 1.2.2 Output Devices The information processed by the computer is translated into a form that we understand, and displayed by these machines. Normally, the output is classified as Softcopy output or Sound output and Hardcopy output. * **Softcopy** refer to data that is shown on a display screen or is in audio or voice form. This kind of output is not tangible; it cannot be touched. Virtual reality and robots might also be considered softcopy devices. **Hardcopy** refer to printed output. The principal examples are printouts, whether text or graphics, from printers, plotters etc. * **Display Screens:** Also known as CRTs, Monitors, or simply screens, differ in size, color, resolution, and video display adapter card. These are used for inputting the data or displaying the information after processing. * **Size:** Monitor come in different sizes, from small screen built into palmtops and laptop to extra large monitors used for special purposes. * **Color:** Many monitors display color. These RGB displays can create 256 colors and several thousand variations on them by blending shades of Red, Green, and Blue (RGB). Monochrome displays show information using a single foreground color on a contrasting background color. * **Resolution:** All the characters and images on a monitor are made up of dot patterns; the number of dot, or pixels, per inch determines resolution, or the sharpness of the image. A higher number of pixels means a shaper image. * **Video Display Adapters:** To display graphics, a display screen must have a video display adapter attached with the computer. It is known as a video graphics card, and is a circuit board that determines the resolution, number of colors, and speed with which images appear on the display screen. So far, there are three types of graphics cards introduced in the market. * **VGA:** Video Graphics Array, support 16-256 colors, depending on screen resolution. At 320 x 200 pixels, it will support 16 colors and at 640 x 480 pixels, 256 colors. It is called 4-bit color. * **SVGA:** Super Video Graphics Array, support 256 colors at higher resolution than VGA. It has two graphics modes: 800 x 600 pixels and 1024 x 768 pixels. It is called 8-bit color. * **XGA:** Extended Graphics Array, supports up to 16.7 million colors at a resolution of 1024 x 768 pixels. Depending on the video display adapter memory chip, XGA will support 256, 65536, or 16,777,216 colors. It is called 24-bit color or True color * **Types of Screen:** Display screens are of two types ie. Cathode-Ray Tubes and Flat-Panel Displays. * **CRT (Cathode-Ray Tubes):** The most common form of display screen is the CRT. A Cathode-Ray tube is a vacuum tube used as a display screen in a computer or video display terminal. This same kind of technology is found not only in the screens of desktop computers but also in television set and in fight- information monitors in airport. A stream of bits defining the image is sent from the computer (from the CPU) to the CRT's electron gun, where the bits are converted to electrons. The inside of the front of the CRT screen is coated with phosphor. When a beam of electrons from the electron gun (deflected through a yoke) hits the phosphor, it lights up selected pixels to generate an image on the screen. **Figure: how CRT screen work** (A diagram of a CRT showing its components) * **Flat-Panel Displays:** The flat-panel displays are much thinner, weightless, and consume less power to CRT. Thus, they are better for portable computers. Flat-panel displays are made up of two plates of glass with a substance in between them, which is activated in different ways. There are three types of technology used in flat-panel display screens: LCD (Liquid-Crystal Display) consists of a substance called liquid crystal, the molecules of which line up in a way that lighting behind the screen is blocked or allowed through to create an image. EL (Electro-Luminescent Display) contain a substance that glows when it is charged by an electric current. Gas-plasma display is like a neon bulb, in which the display uses a gas that emits light in the presence of an electric current. At present, EL and gas-plasma technology are more expensive thus are not used as often as LCD technology. * **Printers:** Printers are used to print characters, symbols, and graphics on paper. They are divided into two categories: * **Impact printers** * **Non-impact printers** * **Impact Printers:** An impact printer forms characters or images by striking a mechanism such as a print hammer or wheel against an inked ribbon, leaving an image on the paper. Following are a few types of impact printers: * **Dot-Matrix printer:** It contains a print head of small pins, which strike an inked ribbon against paper, forming characters or images. Print heads are available with 9, 18, or 24 pins, with the 24-pin head offer the best quality prints. * **Daisy-Wheel printer:** This printer uses a mechanism in the shape of a series of petals arranged on a petal wheel, having a character at the end of each petal. A character comes into a print position by wheel rotation and an image is formed by the hammer strike on the desired character; It is slower than dot-matrix printer but better in quality. * **Line printer:** This type of printer is normally used by mainframe and minicomputers. It prints a whole line of characters at once rather than a single character at a time. Some of these can print up to 3000 lines per 'minute. It is of two types: chain printer and band printer. * **Non-Impact Printers:** Non-impact printer forms characters or images without making direct physical contact between printing mechanism and paper. There are three types in this category. * **Laser Printer:** It is similar to a photocopying machine and it use the principle of dot-matrix printers of creating images with dots. These images are created on a drum, treated with a magnetically charged ink-like toner (powder), and then transferred from drum to paper. The laser printer can produce high quality images of both text and graphics (ranging from 300 dpi to 1200 dpi). Its speed varies from 4-32 text-only pages per minute for microcomputers and up to 200 pages per minute for mainframes. * **Ink-jet Printer:** Ink-jet printer sprays small, electrically charged droplets of ink from four nozzles through holes in a matrix at high speed on to paper. It is cheaper compared to laser printer but lower in resolution (300- 720 dpi) and is slower also (1-6) text-only pages per minute. It has another type of printer i.e. bubble-jet printer, which uses miniature heating elements to force specially formulated inks through print heads with 128 tiny nozzles. * **Thermal Printer:** Thermal printer uses colored waxes and heat to produce images by burning dots on to special paper. The colored wax sheets are not required for black-and-white output. It produces a high quality printout but is quite expensive compared to other non-impact printers. * **Plotters:** A plotter is used to produce high-quality graphics in many colors and used for specialized applications i.e. architectural drawings, maps, graphs, and charts. Plotters are of two basic kinds: * **Flatbed plotter** * **Drum plotter** * **Flatbed Plotter:** A flatbed plotter is the one, which has a paper lying flat on a table-like surface. The bed-size varies according to the need. One to four color pens move across the paper and the images are printed by the computer accordingly. * **Drum Plotter:** It works like a flatbed plotter with a difference that the paper is mounted over a drum, enabling a continuous output. A typical usage is to track an earthquake readings. * **Sound Output:** Speakers are most commonly used to have this type of output. * **Speaker:** As we use microphone to input audio data to the computer, conversely we use speaker to get audio output from the computer. It works on the same principles to convert sound data into machine usable form. A variety of speakers are available in the market to satisfy the requirements of the users. ## 1.3 System Software vs Application Software Generally speaking, a computer is a "deaf and dumb" machine, which cannot do anything at its own unless it is told to do so. We instruct it to do some number calculation, to create/modify a document, to work on some engineering application and so on. So this instruction(s) is the driving force that allows a computer to perform a certain task and known as "a Program or a Software". It is this "Software" that tells the machine's physical components what to do and how to do. The software falls into two major categories i.e. System Software and Application Software. They are discussed as below: ### 1.3.1 System Software The system software basically manages and monitors the different resources of the whole computer system i.e. Operating system, Backup and Restore utility program, drivers etc. Operating system is the main and foremost part of the system software. It is discussed in chapter 7. ### 1.3.2 Application Software Computer Programs or Application software is basically a set of programs that are used to accomplish a given task. It is basically designed and implemented by the computer users or different software houses. The application software is available in many forms/categories ie. Commercial software, scientific software, Financial packages, Games etc. A comprehensive discussion, about how to design and implement the software, is given under the topic "Systems Development" in section 1.5. ## 1.4 Basic Units of Data Storage The memory (main or secondary) is composed of an electronic circuitry, which is a combination of "On" and "Off" switches. This On/Off state has been conceived by the computer's manufacturers as the numbers "1" and "O", as the circuit can show 1 (on state) or 0 (off state) at a given time. Based on these two numbers i.e. 1 and 0 (the binary numbers), the computer can construct sophisticated ways of representing data in the memory. Thus, converting the numbers, alphabets, and characters (and their combinations) into binary digits enable us to represent them in the computer memory. ### 1.4.1 Bit The binary number 1 or 0 is called a bit (for binary digit), which is the basic unit for storing data in the computer memory. The circuit being on or off at a time, a bit in the memory is always storing some kind of data. ### 1.4.2 Byte A byte is a combination of 8-bits, that can store a single character of data (a letter, numeral or special character). The capacity of the memory or the storage is expressed in terms of number of bytes it can hold or store. The following table shows the commonly used storage capacity terms: | Unit | Abbreviation | No. of bytes (approx) | No. of bytes | | :---------- | :------------ | :-------------------- | :----------- | | Kilobyte | K or KB | (2)^10 | 1024 | | Megabyte | M or MB | (2)^20 | About one million | | Gigabyte | G or GB | (2)^30 | About one billion | | Terabyte | T or TB | (2)^40 | About one trillion | **Table 1: Storage Capacity Terms** **Example:** Convert 240 MB of memory in bytes and kilo-bytes? **Solution:** * Number of bytes in one MB = 2^20 * Total number of bytes in 240 MB = 240 * 2^20 bytes * Number of Kilo-bytes in one MB = 2^10 KB = 1024 KB * Total number of Kilo-bytes in 240 MB = 240 * 1024 KB ### 1.4.3 Word A computer word, typically the size of a register, is defined as the number of bits that constitute a common unit of data, as defined by the computer system. The length of a word varies from computer to computer. Generally, the larger the word, the more powerful is the computer. The following table illustrates this factor: | No. of bytes/words | Number of bits | Era of computer | | :------------------ | :------------- | :---------------- | | One byte | 8 | Very early personal computers | | Two byte | 16 | Traditional micro-computers | | Single word | 32 | Mainframes, some mini-computers, and some micro-computers | | Double word (DW) | 64 | Super computers and some micro- computers | **Table 2: Capacity vs Computer Era** **Example:** Convert 60 GB of memory into words? **Solution:** * Number of bytes in one GB = 2^30 * Number of bytes in 60 GB=60*2^30 * Number of words in 4 bytes = 1 W * Number of words in 60 GB 60/4 * 2^30 = 15 * 2^30 words **Remember that:** An 8-bit machine could handle only one-byte (a character) at time, whereas a 64-bit machine handles two words or 8 bytes at a time, making its processing speed eight times faster. ## 1.5 System Development ### 1.5.1 System Components The system comprises of the following necessary components * Hardware * Software * People/Users