Overview

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In the modern world of electronics, the term Digital is generally associated with a computer because the term Digital is derived from the way computers perform operation, by counting digits. For many years, the application of digital electronics was only in the computer system. But now-a-days, digital electronics is used in many other applications. Following are some of the examples in which Digital electronics is heavily used.

• Industrial process control
• Military system
• Television
• Communication system
• Medical equipment
• Radar
• Navigation

Signal

Signal can be defined as a physical quantity, which contains some information. It is a function of one or more than one independent variables. Signals are of two types.

• Analog Signal
• Digital Signal

Analog Signal

An analog signal is defined as the signal having continuous values. Analog signal can have infinite number of different values. In real world scenario, most of the things observed in nature are analog. Examples of the analog signals are following.

• Temperature
• Pressure
• Distance
• Sound
• Voltage
• Current
• Power

Graphical representation of Analog Signal (Temperature)

The circuits that process the analog signals are called as analog circuits or system. Examples of the analog system are following.

• Filter
• Amplifiers
• Television receiver
• Motor speed controller

Disadvantage of Analog Systems

• Less accuracy
• Less versatility
• More noise effect
• More distortion
• More effect of weather

Digital Signal

A digital signal is defined as the signal which has only a finite number of distinct values. Digital signals are not continuous signals. In the digital electronic calculator, the input is given with the help of switches. This input is converted into electrical signal which have two discrete values or levels. One of these may be called low level and another is called high level. The signal will always be one of the two levels. This type of signal is called digital signal. Examples of the digital signal are following.

• Binary Signal
• Octal Signal
• Hexadecimal Signal

Graphical representation of the Digital Signal (Binary)

The circuits that process the digital signals are called digital systems or digital circuits. Examples of the digital systems are following.

• Registers
• Flip-flop
• Counters
• Microprocessors

Advantage of Digital Systems

• More accuracy
• More versatility
• Less distortion
• Easy communicate
• Possible storage of information

Comparison of Analog and Digital Signal

S.N.	Analog Signal	Digital Signal
1	Analog signal has infinite values.	Digital signal has a finite number of values.
2	Analog signal has a continuous nature.	Digital signal has a discrete nature.
3	Analog signal is generated by transducers and signal generators.	Digital signal is generated by A to D converter.
4	Example of analog signal − sine wave, triangular waves.	Example of digital signal − binary signal.

Shortcut Keys

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Short-cut keys Functions
Commonly Used Short-cut Keys
F1	Universal help (for any sort of program).
Alt + F	File menu options in current program.
Alt + E	Edits options in current program.
Ctrl + A	Selects all text.
Ctrl + X	Cuts the selected item.
Ctrl + C	Copies the selected item.
Ctrl + V	Pastes copied item.
Home	Takes the user to the beginning of the current line.
End	Takes the user to the end of the current line.
Ctrl + Home	Takes the user to the beginning of the document.
Ctrl + End	Takes the user to the end of the document.
Shift + Home	Highlights from the current place to the beginning of line.
Shift + End	Highlights from the current place to the end of line.
Microsoft Windows Shortcut Keys
Ctrl + F4	Closes window in program.
Alt + F4	Closes current open program.
F2	Renames the selected icon.
F3	Start find from desktop.
F4	Opens the drive selection when browsing.
F5	Refreshes contents.
Alt + Tab	Switches from one open application to another open application.
Alt + Shift + Tab	Switches backwards between open applications.
Alt + Print Screen	Creates screen shot for current program.
Ctrl + Alt + Del.	Opens windows task manager/reboot.
Ctrl + Esc	Brings up start menu.
Alt + Esc	Switches between applications on taskbar.
Ctrl + Plus (+) Key	Automatically adjusts widths of all columns in Windows Explorer.
Alt + Enter	Opens properties window of selected icon or program.
Shift + F10	Simulates right-click on selected item.
Shift + Del	Deletes selected programs/files permanently.
Holding Shift During Boot-up	Enables boot safe mode or bypass system files.
Ctrl + N	Starts a new note.
Ctrl + O	Opens a recently used note.
Ctrl + S	Saves changes to a note.
Ctrl + P	Prints a note.
Alt + F4	Closes a note and its Journal window.
Ctrl + Z	Helps Undo a change.
Ctrl + Y	Helps Redo a change.
Ctrl + A	Selects all items on a page.
Ctrl + X	Cuts a selection.
Ctrl + C	Copies a selection to the Clipboard.
Ctrl + V	Pastes a selection from the Clipboard.
Esc	Cancels a selection.
Ctrl + F	Start a search tool.
Ctrl + Shift + C	Display a shortcut menu for column headings in a note list.
Microsoft Word Shortcut Keys
Ctrl + N	Creates a new document.
Ctrl + O	Opens an existing document.
Ctrl + S	Saves changes to a document.
F12	Saves the document as a new file.
Ctrl + P	Prints a document.
Ctrl + Z	Helps Undo a change.
Ctrl + Y	Helps Redo a change.
Ctrl + A	Selects the whole document.
Ctrl + X	Helps cut a selection
Ctrl + C	Copies a selection to the Clipboard.
Ctrl + V	Pastes a selection from the Clipboard.
Ctrl + B	Makes selected text bold.
Ctrl + I	Italicizes selected text.
Ctrl + U	Underlines selected texts.
Ctrl + L	Aligns text left.
Ctrl + R	Aligns text right.
Ctrl + E	Aligns text center.
Ctrl + J	Helps justify text.
Ctrl + 1	Sets single line spacing.
Ctrl + 2	Sets double line spacing.
Ctrl + 5	Sets line spacing to 1.5.
Ctrl + Shift + A	Changes characters to all capitals.
Ctrl + D	Inserts a Microsoft Paint drawing.
Ctrl + F	Finds text
Ctrl + Home	Moves to the beginning of the document.
Ctrl + End	Moves to the end of the document.

Development

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In this chapter, we will discuss the development in Computer Science chronologically.

The following table lists down the development −

Year	Development
1959	Transistors: IBM 7090; IBM 1401
1962	NPN transistor
1963	Mouse; CMOS patented
1964	CDC 6600; IBM Data Cell Drive
1966	Integrated circuits: HP 2116A
1966	Apollo Guidance Computer
1969	Honeywell 316
1971	8" floppy disk; ILLIAC IV
1973	Micral first microprocessor PC
1980	Sinclair ZX80, Seagate hard disk drive
1981	IBM PC, Acorn BBC Micro
1983	Apple Lisa; 3.5" floppy
1984	Apple Mac; Apple Lisa 2
1988	Dell
1989	NeXT
1991	Apple Switches to PowerPC
1992	HP 95LX; Palmtop PC
1995	IBM Deep Blue chess computer
1996	USB 1.0
1997	Compaq buys Tandem; CD-RW
1998	iMac
2000	USB 2
2001	Apple iPod
2005	Mac Mini
2006	Apple transition to Intel
2007	iPhone 1
2008	USB 3.0
2010	Apple iPad
2012	IBM zEnterprise System

Abbreviations

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In this chapter, we will discuss the different abbreviations in Computer Science. The following table lists down those abbreviations −

Abbreviation	Full-name
A/D	Analog-to-Digital
ABC	Atanasoff Berry Computer
ACM	Association for Computing Machinery
AI	Artificial Intelligence
ALGOL	Algorithic Language
ALU	Arithmetic Logic Unit
AMD	Advanced Micro Devices
APRANET	Advanced Research Project Agency Network
ASCII	American Standard Code for Information Interchange
BASIC	Beginners All-purpose Symbolic Instruction Code
BCD	Binary Coded Decimal
BIOS	Basic Inpute Output System
BIPS	Billions of Instructions Per Second
BPI	Bytes Per Inch
CAD	Computer Aided Design
CAE	Computer Aided Engineering
CAN	Campus Area Network
CASE	Computer Aided Software Engineering
CD	Compact Disk
CDC	Control Data Corporation
CD-R	CD-Recordable
CD-ROM	Compact Disk Read Only Memory
CD-RW	CD Read/Write
CL	Command Language
CLI	Command Line Interface
COBOL	Common Business Oriented
CODASYL	Conference On Data Systems
CPU	Central Processing Unit
CRT	Cathode Ray Tube
D/A	Digital-to-Analog
DAT	Digital Audio Tape
DBMS	Data Base Management System
DBS	Demand Based Switching
DDL	Data Definition Language
DDS	Digital Data Storage
DEC	Digital Equipment Corporation
DMA	Direct Memory Access
DNA	Digital Network Architecture
DPI	Dots Per Inch
DRAM	Dynamic RAM
DSN	Distributed Systems Network
DTS	Digital Theater System
DVD	Digital Video/Versatile Disk
EBCDIC	Extended Binary Coded Decimal Interchange Code
EDSAC	Electronic Delay Storage Automatic Calculator
EDVAC	Electronic Discrete Variable Automatic Calculator
EFM	Eight-to-Fourteen Modulation
ENIAC	Electronic Numerical Integrator And Calculator
EPG	Electronic Programming Guide
EPIC	Explicitly Parallel Instruction Computing
EPROM	Erasable Programmable Read-Only Memory
FAT	File Allocation Table
FDM	Frequency Division Multiplexing
FEP	Front End Processor
FLOPS	Floating Point Operations Per Second
FM	Frequency Modulation
FMS	File Management System
FORTRAN	FORmula TRANslation
FSK	Frequency Shift Keying
FTP	File Transfer Protocol
GB	Giga Bytes
GFLOPS	Giga FLOPS
GHz	Giga Hertz
GNU	Gnu Not Unix
GPRS	General Packet Radio Service
GSM	Global System for Mobile communication
GUI	Graphical User Interface
HP	Hewlett Packard
HSS	Hierarchical Storage System
HTML	HyperText Markup Language
HTTP	HyperText Transport Protocol
IBM	International Business Machine
IC	Integrated Circuit
IDN	Integrated Digital Networks
IP	Internet Protocol
IrDA	Infrared Data Association
ISDN	Integrated Services Digital Network
ISP	Internet Service Provider
JPEG	Joint Photographic Experts Group
JRE	Java Runtime Engine
JSP	Java Server Pages
KB	Kilo Bytes
KHz	Kilo Hertz
LAN	Local Area Network
LCD	Liquid Crystal Display
LED	Light Emitting Diode
LPM	Line Per Minute
LSI	Large Scael Integration
MAN	Metropolitan Area Network
MAR	Memory Address Register
MB	Mega Bytes
MBR	Memory Buffer Register
MHz	Mega Hertz
MIDI	Musical Instrument Digital Interface
MIPS	Millions of Instructions Per Second
MNP	Microcom Network Protocol
MPEG	Moving Pictures Experts Group
MS-DOS	MicroSoft Disk Operating System
MVT	Multiprogramming with Variable Tasks
NIC	Network Interface Card
NICNET	National Informatics Center NETwork
NOS	Network Operating System
OCR	Optical Character Recognition
OMR	Optical Mark Reader
OS	Operating System
OSI	Open System Interconnection
OSS	Open Source Software
PAN	Personal Area Network
PC	Personal Computer
PDF	Portable Document Format
PDL	Program Design Language
PDP	Program Data Processor
PIP	Peripheral Interchange Program
PROM	Programmable Read-Only Memory
QoS	Quality of Service
RAM	Random Access Memory
ROM	Read Only Memory
SDLC	Software Development Life Cycle
SEQUEL	Structured English QUEry Language
SGML	Syntax for Generalized Markup Language
SIMM	Single In-line Memory Module
SNA	Systems Network Architecture
SNOBOL	StriNg Oriented and symBOlic Language
SQL	Structured Query Language
SRAM	Static RAM
SSI	Small Scale Integration
TB	Tera Bytes
TCP	Transport Control Protocol
TDM	Time Division Multiplexing
UDP	User Datagram Protocol
ULSI	Ultra Large Scale Integration
UPC	Universal Product Code
URL	Uniform Resource Locator
USB	Universal Serial Bus
UTF	Unicode Transformation Format
VAN	Value Added Network
VCR	Video Cassette Recorder
VDT	Video Display Terminal
VGA	Video Graphics Array
VOD	Video-On-Demand
VoIP	Voice over Internet Protocol
VSAT	Very Small Aperture Terminal
WAN	Wide Area Network
WAP	Wireless Application Protocol
WiMAX	Worldwide Interoperability for Microwave Access
WLAN	Wireless Local Area Network
WLL	Wireless Local Loop
WORM	Write Once Read Many
WWW	World Wide Web
XHTML	eXtensible HyperText Markup Language
XML	eXtensible Markup Language
X.400	Electronic Mail Protocol
X.500	Directory Server Protocol

Virus

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A virus is a computer code or program, which is capable of affecting your computer data badly by corrupting or destroying them.

Computer virus has the tendency to make its duplicate copies at a swift pace, and also spread it across every folder and damage the data of your computer system.

A computer virus is actually a malicious software program or "malware" that, when infecting your system, replicates itself by modifying other computer programs and inserting its own code.

Infected computer programs may include data files, or even the "boot" sector of the hard drive.

Types of Virus

Following are the major types of computer virus −

Worms

This is a computer program that replicates itself at a swift pace. Unlike a computer virus, it is self-contained and hence does not need to be part of another program to propagate itself.

Trojan Horse

A Trojan Horse is also a sort of destructive program that remains disguised in a normal software program. It is not exactly a virus, as it cannot replicate itself. However, there is possibility that virus program may remain concealed in the Trojan Horse.

Bombs

It is similar to Trojan Horse, but Logic bombs have some specialty; these include a timing device and hence it will go off only at a particular date and time.

How Does Virus Affect?

Let us discuss in what ways a virus can affect your computer system. The ways are mentioned below −

• By downloading files from the Internet.
• During the removable of media or drives.
• Through pen drive.
• Through e-mail attachments.
• Through unpatched software & services.
• Through unprotected or poor administrator passwords.

Impact of Virus

Let us now see the impact of virus on your computer system −

• Disrupts the normal functionality of respective computer system.
• Disrupts system network use.
• Modifies configuration setting of the system.
• Destructs data.
• Disrupts computer network resources.
• Destructs of confidential data.

Virus Detection

The most fundamental method of detection of virus is to check the functionality of your computer system; a virus affected computer does not take command properly.

However, if there is antivirus software in your computer system, then it can easily check programs and files on a system for virus signatures.

Virus Preventive Measures

Let us now see the different virus preventive measures. A computer system can be protected from virus through the following −

• Installation of an effective antivirus software.
• Patching up the operating system.
• Patching up the client software.
• Putting highly secured Passwords.
• Use of Firewalls.

Most Effective Antivirus

Following are the most popular and effective antivirus from which you can choose one for your personal computer −

• McAfee Antivirus Plus
• Symantec Norton Antivirus
• Avast Pro Antivirus
• Bitdefender Antivirus Plus
• Kaspersky Anti-Virus
• Avira Antivirus
• Webroot Secure Anywhere Antivirus
• Emsisoft Anti-Malware
• Quick Heal Antivirus
• ESET NOD32 Antivirus

Threat

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Threat in a computer system is a possible danger that might put your data security on stake. The damage is at times irreparable.

Definition

As defined by the National Information Assurance Glossary −

• “Any circumstance or event with the potential to adversely impact an IS through unauthorized access, destruction, disclosure, modification of data, and/or denial of service.”

• A computer threat can be "intentional" such as hacking or "accidental" such as malfunctioning of or physical damage.

Types of Threat

Following are the most common types of computer threats −

• Physical damage − It includes fire, water, pollution, etc.

• Natural events − It includes climatic, earthquake, volcanic activity, etc.

• Loss of services − It includes electrical power, air conditioning, telecommunication, etc.

• Technical failures − It includes problems in equipment, software, capacity saturation, etc.

• Deliberate type − It includes spying, illegal processing of data, etc.

Some other threats include error in use, abuse of rights, denial of actions, eavesdropping, theft of media, retrieval of discarded materials, etc.

Sources of Threat

The possible sources of a computer threat may be −

• Internal − It includes employees, partners, contractors (and vendors).

• External − It includes cyber-criminals (professional hackers), spies, non-professional hackers, activists, malware (virus/worm/etc.), etc.

Common Terms

Following are the common terms frequently used to define computer threat −

Virus Threats

A computer virus is a program designed to disrupt the normal functioning of the computer without the permission of the user.

Spyware Threats

Spyware is a computer program that monitors user’s online activities or installs programs without user’s consent for profit or theft of personal information.

Hackers

Hackers are programmers who put others on threats for their personal gain by breaking into computer systems with the purpose to steal, change or destroy information.

Phishing Threats

It is an illegal activity through which phishers attempt to steal sensitive financial or personal data by means of fraudulent email or instant messages.

How to Secure Your Computer System from Threats?

Following are the significant tips through which you can protect your system from different types of threat −

• Install, use, and keep updated Anti-Virus in your system.
• Install, use, and keep updated a Firewall Program.
• Always take backups of your important Files and Folders.
• Use Strong and Typical Passwords.
• Take precaution especially when Downloading and Installing Programs.
• Install, use, and keep updated a File Encryption Program.
• Take precaution especially when Reading Email with Attachments.
• Keep your Children aware of Internet threats and safe browsing.

Security

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Advancement of computer technology has radically changed the world; resultantly, most of the works whether it is matter of nation’s security system or buying a shoe online everything depends on computer.

Such increased dependency also raises the issue of security, as most of the data is now stored in the computer system.

Your computer systems store various sorts of data and hence if it is not secured, then you might be in for a big trouble.

Why Do We Computer Security?

Let us now see why do we need Computer security. It is required for the following major reasons −

• To prevent damage of the hardware.

• To prevent theft or damage of the installed software.

• To prevent theft or damage of stored data and information.

• To prevent the disruption of service.

• Likewise, security system keeps the computer system safe by protecting the installed software and the stored data (information).

Protection of Data and Information

Following are the important steps to protect data −

• Make backup of all your important files.
• Keep your system virus by using anti-virus software.
• Keep updating your computer system.
• Run disk defragmenter and disk cleanup on certain interval of time.
• Use a firewall.
• Use anti-spyware software.

Further, if you use internet, then you need to take greater precaution. Consider the following points to understand the precautions that need to be taken −

• Do not click on any link that you don’t know (as it may be dangerous for your computer - virus attack).

• Do not open unauthorized an unlawful website (it may damage your computer system).

• Do not download unsolicited data from unknown website.

What is Defragmentation?

Frequent saving and deleting of file (data) from the hard disk creates problems in performance and also reduce the space; therefore, defragmentation again clean-up the drive and restore the system to run smoothly.

Following are the simple steps of defragmentation −

Disk Cleanup

While browsing websites (on internet), many of the files get stored in the hard disk automatically (actually these stored files later help to reopen the website faster); besides some other cookies also get stored in the hard disk. All these stored files create problem along with eating space.

So, disk cleanup process cleans all these files and releases the space occupied by these unwanted files.

Following are the simple steps of disk cleanup −