Data Organization

It has been mentioned earlier that in a computer system, the data that is input gets converted into information. We also identified the need for external storage media on which data can be stored for future use.

In our day-to-day lives, we store information in the form of files, be it our telephone directory, or the record of our monthly expenditure. The medium that is used in this type of manual storage is usually paper or other such physical media.

Similarly, information is also stored on the computer in the form of files, but the media is either external storage or internal storage. A computer may have the following types of files on its storage media:

• Text files
• Data files
• Graphic files

Types of Files

Text Storage on a Storage Media

Example of a Text File

Any kind of text information, be it letters, documents or memorandums, is stored on the computer in the form of a file, which may be broadly classified as a text file. An example of a text file is shown in Figure.

Data Storage on a Storage Media

A Manual Data File

Let us now look at how a company manually stores its data. In a manual system, data is stored in the form of a file. A manual file may contain the particulars of each employee in a company (refer Figure).

The manual employee file of a company has several cards, each with the details of one employee. The data to be used in a computer is also stored on a storage media i.e. the floppy disk or hard disk, in the form of a data file. However, a computer data file does not look like a manual data file. Data in a computer file is organized in a different manner (refer Figure).

A Computer Data File

where

DESIG = designation

DEPT = department

AGE = age of the employee.

In a computer file, the particulars of each employee are contained in a single line. This is referred to as a record. For example, the complete data about employee ANN MURRAY, regarding his designation, department and age, is one record. Thus, a computer file is more compact than a manual file.

Each piece of data in the record is called a field. A field has two components—the field name and the field content (refer Figure). NAME, DESIG, DEPT and AGE are field names. Each record in the file contains these four fields. The field contents are JOHN BROWN, MARY MILLER, CONSULTANT, HRD, 52, etc. The contents of a field usually differ from record to record. You will recall that a character is any alphabet, numeral or symbol, such as %, *, etc. Each field comprises a number of characters. To sum it up, a field comprises several related characters, various related fields make up a record and many such records make up a file (refer Figure). Fields in the records have names.

Graphic Storage on a Storage Media

Example of a Graphic File

The computer is also capable of storing pictures, moving videos, sketches and other forms of visual information. This type of information is stored in the form of files that may be broadly classified as graphic files. An example of a graphic file is shown in Figure.

Software

A PC is incapable of performing any task with the hardware alone. It requires instructions that determine whether it will function as desired or not. Like data, instructions are also entered via the keyboard. In computer terminology, a set of instructions is called a program and one or more programs are called software.

Software used on computers may be of different types. Some important classes of software are:

• Application software
• The Operating System

Application Software

We spoke of computer applications and identified certain areas where computers are being used today. Software specially suited for specific applications is now available in the market. For example, software for billing systems, accounting software or software that enables the creation and storage of documents. Such software is called application software since it is designed for a specific application.

Application software that takes care of a variety of business and corporate needs can now be bought off the shelf. These are also called standard software packages. They are reasonably priced and can run on any standard PC.

Two popular standard software packages are Financial Accounting and Inventory Control packages.

In case a user is not satisfied with the available package, because it does not meet all the requirements, the package can be modified.

However, if the package cannot be modified, the user can opt for a customized software package. A customized package is developed for a user's specific needs and may not be relevant to any other user.

Though these packages are for very specific applications, there are general application softwares like database management systems (DBMS), spreadsheets and word processors.

Using a DBMS software, a user can maintain large volumes of data that can be modified, updated and queried.

A spreadsheet package allows a user to enter numeric data, specify formulae and perform calculations. Graphs can also be generated from the given data. The special feature of automatic recalculation allows changes made in any one item to reflect in all items dependent upon the first one.

A word processing package converts a PC into a sophisticated typewriting machine. It has the facility to perform spell checks, provide for synonyms, and allow changes or corrections in the document without having to re-type the entire document.

Compiler Software

Consider the case of four persons, Leonardo, Chou, Ivan, Hari, who understand and speak Spanish, Chinese, Russian and Hindi, respectively. To be able to understand each other, they would require some person or persons who could translate whatever is spoken into the language each understands.

Similarly, since there are so many programs written in different computer languages, the hardware also needs a translator to convert the computer language into a form that it can understand.

The computer only understands a language of electrical signals, called machine language.

Software called the compiler converts the computer language into machine language. For example, there is a C compiler that converts programs written in the C language to machine language.

Operating System

Besides the application software and compiler software, there is a third kind of software, called the operating system, which is very important for the working of the PC.

When a user wants to store any data or program, the data or program is stored at a location that is known only to the operating system. Therefore, the operating system performs the task of storage management.

Besides storage management, the operating system also performs device management. For instance, when a user wants to print information on the printer, or display information on the VDU, he or she does not have to bother about the actual transportation of the information from the internal storage to the VDU or to the printer. The operating system takes care of it.

Computer Languages

All application software packages are written in computer languages. There are various computer languages like C, C++, FORTRAN and Pascal. Each language is best suited for a particular application.

C and C++ languages are used to develop highly complex software. FORTRAN is used for scientific applications

Each language has its own vocabulary. There are some packages like FoxPro, MS Access and Sybase that are more English-like. Thus, even non-computer professionals, like executives and managers who have never studied computer science, can learn to use these languages.

Since each language has its own vocabulary, each language differs from the other.

Disk Drives

We have identified the need for an external storage media and made a comparison between two popular forms of storage media—the hard disk and the floppy disk. However, the microprocessor does not perform the task of writing on or reading from this media. A device specially designed to perform these functions is the disk drive.

Data is fed into the PC and written on the hard disk or the diskette by the disk drive. When the data is to be processed, it has to be read from the disk before processing actually takes place. The disk drive also performs this function of reading the data. Since the disk drive performs both the tasks of writing and reading the data, in other words, the input and output functions, it is referred to as an \nput-output device.

A simple analogy of how a disk drive works is the cassette tape recorder. It encodes music and stores it on a cassette tape as a series of signals. It also reads the stored signals on the cassette tape and converts them back to music. The cassette player records as well as plays back the music. Therefore, it performs both reading and writing. A disk drive works in much the same way, reading and writing whenever required.

The disk drive is contained within the system unit. The drive for a diskette is called a diskette drive while the drive for a hard disk is called the hard disk drive.

It is important to differentiate between the storage media and storage devices. While the diskette and the hard disk on which data is stored are the storage media, the disk drives are the devices that do the reading and writing. Going back to the analogy of the cassette tape recorder mentioned earlier, the cassette tape would be called the storage medium while the cassette player is the storage device.

External Storage

Since the internal storage capacity of PCs is limited, it places a restriction on how much data can be stored at a time for processing. However, this is not the only drawback. Once the PC is switched off, or in case of a power failure, all the data stored in the internal storage is lost. This means that every time you want to work on the PC, you would have to input the data required for processing.

For permanent storage of data, external storage media can be used with a PC system. External storage is also referred to as secondary storage.

There are two kinds of external storage media used with a PC, they are:

• Floppy Disk
• Hard Disk

Another media for external storage is the cartridge tape. It is particularly suitable for storage of large volumes of data. Now, CD-ROMs and Magneto-Optical (MO) disks have also become an important media to store large volumes of data.

Floppy Disk	Hard Disk
Also referred to as diskettes or floppies.	Also referred to as the fixed disk.
Removable. Suitable for moving data from one computer to another.	Non-removable. It is attached within the system unit.
Made of flexible vinyl material. Less resistant to damage by heat, dust and accidental twists.	Less prone to damage since it is within the system unit and is packed airtight.
The diskettes currently in use have a diameter of 3.5 inches with a storage capacity of 720KB or 1.44MB.	Can store data in the range of 20 MB to a few GB.
Diskettes having a diameter of 5.25 Inches and a typical storage capacity of 360KB is also used, but is slowly being phased out.

Comparison between a Diskette and a Hard Disk

Internal Storage

Besides the microprocessor, the system unit also contains a storage area where the data is stored before being actually processed. This storage area is called the internal storage. It is also referred to as primary storage, main memory ox Random Access Memory (RAM).

Internal storage capacities may differ in different PCs. Typically; a PC will have an internal storage capacity of 640,000 characters or more.

In computer terminology, the storage capacity of a PC is measured in terms of bytes, where one byte can store one character. Character here refers to any alphabet, number or other symbol. Therefore, to store the word COMPUTER, 8 bytes would be required. Just as there is a basic unit, gram, and another unit, kilogram to measure weight, there is also byte and kilobyte (KB) to measure storage capacity. One KB is approximately equal to 1000 bytes. Therefore, 1 KB can store approximately 1000 characters. Another common unit of measurement of storage capacity is the megabyte (MB), which is equal to approximately 1000 KB. Very large storage capacities are measured in terms of gigabytes (GB). One GB is approximately equal to 1000 MB.

Comparison Between Printers

The output on the VDU cannot be stored for later reference. For a permanent output, you would require a printer that is also a common output device. Using the printer, you can obtain output on paper. Printers are capable of printing at very high speeds. The printers commonly used with the PC are the dot-matrix printer, the ink jet printer and the laser printer.

Dot matrix Printer	Ink-jet Printer	Laser Printer
Prints characters formed of dots	Prints fully formed characters	Prints fully formed characters
Speed: 200-540 characters per second	Speed: 4-8 pages per minute	Speed: 4-20 pages per minute
Accepts up to 132-column stationary	Accepts up to 80-column stationary	Accepts up to 80-column stationary
Inexpensive	Moderately priced	Expensive

Comparison between Printers

Visual Display Unit (VDU)

Now that you are familiar with some input devices of the computer, let us take a closer look at an output device. Data that has been processed needs to be displayed to the user. This is done using the monitor or the VDU. The VDU is similar to a TV screen and can display both text and graphic images. The display can be either in black & white or color.

Keyboard

The keyboard has already been identified as an input device. This is a component that closely resembles a typewriter console.

While working on the PC using a keyboard, you will notice a flashing point on the VDU. This is the cursor. When you press a key on the keyboard, a character is displayed at the point where the cursor is flashing and the cursor moves one position forward. The keyboard provides different keys to perform various operations.

Key	Function
F1- F12 (Function keys)	Used to perform special functions that depend on the software being used.
Enter or Return	Used to execute an instruction or data being keyed in through the keyboard
Caps lock	Used for keying in capitalized alphabets.
Shift	Capslock off: If pressed simultaneously with a character key, a capitalized alphabet is input. Capslock on: It reverses the above effect. Also used to input the upper symbols for keys with two symbols or characters on them.
Ctrl, Alt	Pressed with other keys, they input special messages to the computer.
Backspace	Used to erase the character to the left of the cursor position.
Numlock	Used to activate the numeric keys on the Numeric keypad.
Cursor keys	Used to move the cursor in the direction indicated.
Home, End, PgUp, PgDn	Used to perform special functions, with which you will become familiar during the course.
Ins	Used to insert characters at the current cursor position.
Del	Used to delete characters at the current cursor position.
Esc	Depends on the application. Usually used to cancel a command.
Print Screen	Used to print whatever is displayed on the screen.
SysRq	System Required; depends on the application.

The Keys and their Functions

Benefits and Limitations of Computers

The fact that computers have made their impact on almost all aspects of life in today's world can hardly be questioned. The question that you may ask here is how do you benefit from using a computer.

A computer provides three basic benefits:

• Speed
• Accuracy
• Diligence

Computers work at very high speeds and are much faster than humans. The human equivalent of an average computer would be one million mathematicians working 24 hours a day. Computers rarely make mistakes. In fact, most computer errors are caused by human frailties. Unlike humans, computers simply do not get bored or tired. The monotony of repetitive work does not affect computers.

However, computers cannot take over all activities simply because they are less flexible than humans. They have to be explicitly told what to do. They cannot perform anything outside the defined scope. If an unanticipated situation arises, computers will either produce erroneous results or abandon the task altogether. They do not have the potential to work out an alternative solution.

Other Computer Systems

The PC is although the most popular computer system, there are other computer systems too, which are categorized on the basis of size, cost and performance.

Before we describe some of these computer systems, it is essential to understand the term system. A system is a group of integrated parts that have a common purpose of achieving an objective. These parts or components of the PC system will be discussed in detail later in the course.

A popular computer system is the mini-computer, which is a small, general-purpose computer. It can vary in size from a small desktop model to the size of a small filing cabinet. A typical mini system is more expensive than a PC and surpasses it in storage capacity and speed. While most PCs are oriented towards single users, mini systems are usually designed to simultaneously handle the needs of multiple users, i.e. more than one person use a mini-computer at the same time.

A mainframe is another form of a computer system that is generally more powerful than a typical mini system. Mainframes themselves may vary widely in cost and capability. They are used in large organizations for large-scale jobs.

However, there is an overlap between the expensive minis and small mainframe models in terms of cost and capability. Similarly, there is an overlap between the more powerful PC systems and the mini computer.

At the end of the size and capability scale are the supercomputers. These systems are the largest, fastest and the most expensive computers in the world. They are used for complex scientific and defense applications.

How Does a Computer Work?

Most activities follow the basic principle of Input-Process-Output. Consider an automobile assembly line. The raw materials required by an automobile assembling unit would include body, engine parts, tires, and so on.

These materials are forwarded to the assembling unit. This activity constitutes the input part of the cycle. The process is the actual building of the automobile. Therefore, the process acts upon what has been the input and produces the output, which in this case would be the finished automobile.

l-P-0 Cycle in an Automobile Manufacturing Unit

Like all other activities, a computer system too follows the Input-Process-Output or l-P-0 cycle. This can be best illustrated by an example of an airline reservation. A person who wishes to travel by air between Singapore and New York first has to fill in a request slip. This slip contains relevant data, i.e. details of name, age, place of destination, etc. The booking clerk keys in the data from the request slip into the computer. The process in this case includes examining the flight number, the date of the journey, the class requested, and determining whether seats are available as per the reservation details. The output of this process is some information confirming the booking, if seats are available. Otherwise, a message may be issued by the computer turning down the request.

Atlantis Airways
From: Singapore	To: New York
Name Age Date of Journey Time Class	Sally Chang 25 23rd November 1995 7.30p.m. Executive

Example of Output in an l-P-0 Cycle

Now let us see how each component of the PC system is related to the l-P-0 cycle. The data in the request slip is input into the computer via the keyboard. Hence, the keyboard is an input device. The processing is performed by a component of the system unit called the microprocessor. The information regarding , availability of seats is displayed on the VDU. Hence, the VDU is an output device.

The l-P-0 cycle components of a PC

The term hardware is used to refer to the physical components of a computer system. Thus, hardware comprises the input and output devices along with the system unit.

Managing Data and Software

Introduction

Before looking into data and software management, let us find out what is disturbing Mr. Croft of Croft Constructions. He and his employees seem to be having problems using computers in their office. The problems are related to managing data and software. Here are the problems as described by them.

Croft: On Thursday, I employed Sally, and decided to put her to work on the computer immediately. As Betty was using one of the machines, I asked her to use the other. This machine did not have MS Word. So I took out the original diskettes and began to load MS Word. To my dismay, I found that the diskettes were corrupted. I called up my software dealer and got another copy the next day. This meant a day wasted for Sally.

Betty: Mr. Croft wanted a list of clients based in New York. I had been updating the database file on both machines and could not remember which machine I had worked on last. As a result, I had to manually check the files. A waste of time and effort. Further, Mr. Croft does not want information about his clients falling into unauthorized hands. I keep files containing client information only on floppy disks, which means unloading and loading the diskettes each time I want to update the files,

Sally: As I was typing a letter for Mr. Croft, I found the message, Your PC is now STONED!', displayed on the screen. As I did not know what it was, I ignored it. Later Mr. Croft discovered that it was a virus. We had to do a major cleaning operation to get rid of the infection.

The above situation highlights some common problems of data and software maintenance. These problems can be easily rectified by maintaining multiple copies of data and software, hiding files containing confidential information and protecting files from viruses. These and related issues will form the contents of this session.

• Master and Working Copies of Data and Software
• Managing Floppy Disks
• Identification Of Data And Software
• Security Write Protecting Floppy Disks
• Handling Floppy Disks
• File Access
• Machine Access
• Protecting Data and Software from Viruses
• Effects Of Viruses
• Types Of Viruses
• File Virus
• How Boot-sector/Partition-table Virus damages your Computer
• Stealth Virus
• Virus Detection And Cleaning
• Virus Attack Symptoms
• Anti Virus Programs
• Virus Preventior
• Worms And Trojan Horses

Master and Working Copies of Data and Software

Smallville High School had a file containing the names and marks of its students. While working with the diskette, the Principal accidentally deleted all the files. The results of the students could not be given on time.

The above mentioned problem would not have arisen if the Principal had additional copies of the same set of files.

Consider another situation. Suppose you open a file which contains a letter. To make modifications to it, you will open it, modify it and save the modified letter in the same file. If the power fails when you are saving the file, there is a chance that the data will get damaged. A damaged file is called a corrupted file in computer jargon. Now you will have to write the letter again, unless you had made a copy of the letter earlier. An additional copy of a file is called a backup.

Most computer users keep two or three copies of the same file. The original copy of data/software is called the master copy and the duplicates you make are called working copies. Most users use only the working copy so that the original is always available for emergencies. For example, the master copy will be useful if your hard disk crashes (a hard disk is said to have crashed if all the data and software stored in it cannot be accessed) and your working copy gets corrupted. Or, take the case when you are using your data after a long time. If the duplicate is corrupted, either due to bad storage or maintenance problems, you can always use the master.

Backing up is the process of archiving data and software. Since the amount of data to be backed up is usually very large (sometimes in excess of 500 MB), backups are typically taken on storage mediums like CD-ROM, cartridge tapes and M-0 disks. Most operating systems provide facility for backing up data and software.

Windows NT provides a utility for backing up and restoring files from tape drives. Windows NT Backup is a graphical tool for protecting data from accidental loss or hardware or media failures. NT Backup makes it easy to use a tape drive to backup and restore important files on the system.