Unit 1 Introduction to Computer Organization and Architecture Introduction

In this unit you shall be introduced to the concept of a computer. The unit explores the definition and parts of the computer. It puts emphasis on the input, process, storage and output parts of the computer. The unit emphasises the concept of a computer as a system rather than a simple entity of processing. The difference between data and information shall also be covered.

By the end of the unit the student should be able to:

1. 
   Define the term computer
   
2. 
   Explain the concept of a computer as a system
   
3. 
   Describe the functions of different parts of the computer system
   
4. 
   Name various input and output devices.
   
5. 
   Give the functions of various storage devices.
   

A computer is an electronic device that stores, accepts data, retrieves data, processes data and gives output according to a set of instructions. Business dictionary defined a computer as a general purpose machine, commonly consisting of digital circuitry, that accepts (inputs), stores, manipulates, and generates (outputs) data as numbers, text, graphics, voice, video files, or electrical signals, in accordance with instructions called a program

 http://www.businessdictionary.com/definition/computer.html#ixzz3yNEZwJhN Accessed 26/01/2016

Elements of a computer

• 
  Hardware is the collection of physical elements that constitutes a computer system. Computer hardware is the physical parts or components of a computer you can touch and see, examples of computer hard ware include  monitor/screen, mouse, keyboard,  hard disk drive (HDD), graphic cards, sound cards, memory, motherboard, and so on. All these are physical objects that are tangible.
  
• 
  Software: Software is any set of machine-readable instructions that directs a computer's processor to perform specific operations. Software refers to instructions that can be stored and run by hardware. A combination of hardware and software constitutes a usable computer system
  
• 
  User: An individual who uses a computer. This includes expert programmers as well as novices. An end user is any individual who runs an application program. Users generally use a system or a software product without the technical expertise required to fully understand it.
  

Figure 1 a: The structure of the computer

(Adapted from http://ourjobs123.blogspot.com/2014/10/Computer-Basics-for-Bank-online-Aptitude-Tests.html)

Hardware

• 
  This is the equipment that makes up a computer system (physical components).
  
• 
  Many of these parts are contained within the computer’s case.
  
• 
  Other parts are external but connected to the computer (peripheral devices). These allow data to be entered (input) and retrieved (output) and stored.
  

• 
  CPU
  
• 
  Mother Board
  
• 
  RAM
  
• 
  Sound Card
  
• 
  Video Card
  
• 
  Hard Drive
  
• 
  DVD
  

• 
  Keyboard
  
• 
  Mouse
  
• 
  Printer
  
• 
  Scanner
  
• 
  Monitor
  
• 
  Speakers
  

• 
  Processing devices (processor)
  
• 
  Output devices (monitor, speakers and printer) display data
  
• 
  Storage devices (memory sticks and disks) hold data
  

• 
  The part of the computer performs the bulk of data processing operations is called the central processing unit
  
• 
  “Brain” as well as “heart” of computer system
  
• 
  The chip or chips at the heart of a computer that enable it to process data.
  
• 
  It is very easy to replace because it is inserted into the socket and is not soldered onto the motherboard
  

• 
  The CPU is made up of four major parts:
  
  • 
    Register set
    
  • 
    ALU
    
  • 
    Control unit
    
  • 
    Main memory
    
    • 
      Memory: An area within a computer system that holds data waiting to be processed.
      

• 
  Control unit
  

• 
  Arithmetic logic unit (ALU)
  

• 
  Set of registers
  

Stores intermediate data during the execution of instructions;

• 
  Primary functions
  

Store information about currently executing program and about status of CPU (special-purpose registers)

• 
  Input is any data entered into the computer’s memory.
  
• 
  input devices : the devices that allow data and instructions to enter a computer (such as a keyboard, mouse, scanner)
  
• 
  Each type of input device has an INTERFACE i.e. a means of communication between the human user and the electronic computer.
  

• 
  Data may be keyed in from source documents by keyboard operators
  

• 
  Computer Keyboard
  
• 
  Numeric keypad
  

• 
  The source documents may be read directly by a document reader. Document readers capture information in the form of pictures or text already printed on paper.
  

• 
  Image Scanners
  
• 
  Optical Character reader (OCR)
  
• 
  Optical Mark reader (OMR)
  
• 
  Magnetic ink character reader (MICR)
  
• 
  Bar code readers
  

• 
  Data may be captured directly without the need for any source document
  

• 
  Magnetic strip on a plastic card,
  
• 
  Smart card
  

• 
  Graphic input devices may be used to translate drawings or photographs into digital form that can be processed by a computer
  

• 
  Mouse
  
• 
  Track ball
  
• 
  Touch screen
  
• 
  Digitizing tablet
  
• 
  Light pen
  

• 
  A microphone can be attached to a sound card to provide audio input and also to issue commands and crate files
  
• 
  Speech recognition is a type of input in which the computer recognizes words spoken into a microphone.
  

• 
  Output devices are peripheral devices that enable us to view or hear the computer’s processed data. E.g. a display screen or printer)
  
• 
  Output: The product of the transformation of inputs by a process.
  

Computer output refers to that which is output by the computer to the outside world e.g. sound.

• 
  Types of output
  
  • 
    Visual output – Text, graphics, and video
    
  • 
    Audio output – Sounds, music, and synthesized speech
    

Monitors

• 
  A monitor is a peripheral device which displays computer output on a screen.
  
• 
  Screen output is referred to as soft copy.
  
• 
  Types of monitors:
  
  • 
    Cathode-ray tube (CRT)
    
  • 
    Liquid Crystal Display (LCD or flat-panel)
    

• 
  A printer is a peripheral device that produces a physical copy or hard copy of the computer’s output.
  

• 
  Laser printer works like a copier
  
• 
  Quality determined by dots per inch (dpi) produced
  
• 
  Color printers available
  
• 
  Expensive initial costs but cheaper to operate per page
  
• 
  Inkjet printer
  
• 
  Inkjet, is also called a bubble-jet, it makes characters by inserting dots of ink onto paper.
  
• 
  Letter-quality printouts
  
• 
  Cost of printer is inexpensive but ink is costly
  

• 
  A plotter is a printer that uses a pen that moves over a large revolving sheet of paper.
  
• 
  It is used in engineering, drafting, map making, and seismology.
  

• 
  Audio output is the ability of the computer to output sound.
  
• 
  Two components are needed:
  
  • 
    Sound card – Plays contents of digitized recordings
    
  • 
    Speakers – Attach to sound card
    

• 
  Storage device:
  
  • 
    The place where a computer puts data.
    
  • 
    The area within a computer system where data can be left on a longer term basis while it is not needed for processing.
    

• 
  Storage devices:
  
  • 
    Retain data when the computer is turned off
    
  • 
    Are cheaper than memory
    
  • 
    Play an important role during startup
    
  • 
    Are needed for output
    

• 
  Magnetic – Storage devices use disks or tapes that are coated with magnetically sensitive material
  
• 
  Optical – Storage devices that use laser beams to read patterns etched into plastic disks
  

• 
  CD-ROM stands for Compact Disc-Read Only Memory.
  
• 
  CD-ROM drives cannot write data to discs.
  
• 
  They are capable of storing 650 MB of data.
  
• 
  They are used for storing operating systems, large application programs, and multimedia programs.
  

CD-R

• 
  Discs can be read and written to
  
• 
  Discs are erasable
  
• 
  Discs can be written to many times
  
• 
  CD-RW drives are capable of reading, writing, and erasing data
  

• 
  DVD stands for Digital Video Disc.
  
• 
  DVD technology is similar to CD-ROM technology.
  
• 
  DVDs are capable of storing up to 17GB of data.
  
• 
  The data transfer rate of DVD drives is comparable to that of hard disk drives.
  
• 
  DVD-R and DVD-RW drives have the ability to read/write data.
  

• 
  Solid state storage devices use nonvolatile memory chips to retain data.
  
• 
  They do not have moving parts.
  
• 
  They are small, lightweight, reliable, and portable.
  

Memory Stick

Compact Flash Memory

Micro Drive

UNIT 2: The windows environment

Before you work with different computer applications you need to be familiar with the windows environment. It is this environment that you will be using in performing different tasks with your computer. For simplicity and standardisation, this module shall use windows 7 operating system environment as well as Microsoft Office 2007 applications. Please note that this work is not to promote a certain software producer but to impart knowledge and skills to students. After going through explanations and examples in this module, the student is advised to try exploring the same concepts in different hardware and software environments.

The windows aspects that you shall learn in this section include the desktop, the general office window and its sections, folder management and basic windows tools.

The desktop

Figure 2b shows how the desktop looks like. Note that the background differs according to the individual user preferences, so expect to see different desktop backgrounds whenever you encounter a different desktop. The desktop is what you see when the computer has finished booting up. It is equivalent to the top of your desk when are working in your office. You may remember that on your desk there are all tools that you need to do your daily tasks. On one’s desk we would expect to see pens, rulers, calculators, diaries, trays and so on. On the sides of the desk you may have a dust bin to throw unwanted papers.

The emergence of the electronic office resulted in converting all those functions into electronic form. We now have pens, rulers, recycle bin and other tools that we need to use in our electronic office that makes minimum or no use of papers. Next we are going to explore the different tools that we have on our desktop.


Standard desktop icons

User created folders

Saved document

Other icons

On standard widows desktop there are icons which are there and are expected to be there. On figure there are two standard desktop icons namely Computer and Recycle bin. As a user you can also create your own folders on the desktop in which you save your work. In figure we have two folders named, All others and ITCA work. A user can create as many desktop icons as required. However, it is advisable to have very few icons on your desktop so as to avoid cluttering it. You need to plan how your work needs to be organised carefully. You may need to have as few as five main folders on your desktop possibly corresponding to all the modules you are doing that semester. If you are doing communication, introduction to computers, Statistics, Entrepreneurship and Life skills; you may need to create a folder for each of the five. Then in each folder you can create more folders e.g. tutorials, lecture notes, self notes, exercises and assignments. The subfolders may also be subdivided into sub-sub folders. If you practice this you will notice that it will be a lot easier for you to locate anything of interest.

One can also save documents on the desktop be it word, spreadsheet, database, presentation etc. On figure the word document Automatic gate system was saved on the desktop. Note that it is not good computing practice to save documents directly on the desktop.

The desktop can also carry certain icons that are often used for example in figure there is Google chrome and Skype. Some software when installed on your computer will automatically put a desktop icon for easy access to it.

At the bottom of Windows 7 desktop window there is a series of icons corresponding to major applications running on the computer as well as active program icons. Figure shows such icons.




Word

Start button

Folders

Mozilla Firefox



Internet explorer

Media player

Skype

Basic operations in the Windows environment

Before you proceed to the next sections of this module, you have to acquaint yourself with the following basic operations:

• 
  Opening a document
  
• 
  Saving a document
  
• 
  Backing up a file
  
• 
  Print previewing a document.
  

Word processing involves creating textual documents using your computer as well as saving and printing those documents. The documents may be letters, memos, reports, assignments, etc. In your studies you will be required to write many of such documents. It is therefore critical that you are competent in word processing. The skills you will acquire in this area will be useful in writing your assignments and projects in your programme, at home and at work.

This module will not cover everything in word processing but limited to the structure of word processing window and a few word processing activities enough for building a base for your work.

The word processing window

Figure shows the main elements of the word processing window.

The grey area at the center of the window is called the work space or working area. You type all your work in this area. Let us explore the various parts of this window in the following sections.

The office button is found on the top left corner of the window. Clicking on the office button will produce the drop down menu as shown in figure below:

The drop down menu is comprised of new, open, save, save as, print, prepare, send, publish and close. These are the standard actions that you can perform while working on your documents. In your practical session you will familiarise with all these actions. You use the new action when you intend to create a new document e.g. a memo or a letter. The open action is used to open an existing document that has been saved either in the computer hard disk or any external storage device e.g. a memory card or memory stick.

The office button can also help you access any recently opened documents without bothering you with remembering where you saved the document. In this case the recent documents are listed thus ITCA module, Farai CV Telecel etc.

Tool bar

The tool bar contains standard tools that you can use to do several things while working with your document e.g. copying, pasting, indenting changing font colour and so on.

As the name implies this is the position where the name or title of the document name is located. Once you save your document the name that you give to the document is the once that is written in this bar. Figure shows that the document I was working on is called ITCA Module which is a Microsoft word document.

The main menu contains several menu items that are used in working with your documents. Every action starts here. These are called main menu items because once you click on each of them a different set of sub items are displayed allowing you to perform certain specific actions. Figure shows the main menu and its menu items.

The main menu items are the Home, Insert, Page layout, references, mailings, Review and View. Each of these menu items has several submenus corresponding to it. If you click on any of these items a different set of submenus will be displayed. Figure and figure show the submenus of Home and Insert respectively. You shall learn the use of each of the items in the submenus in your practical sessions.

The submenus of Home are Clipboard, Font, Paragraphs, styles and Editing.

The insert menu option has the submenus Pages, Tables, Illustrations, Links, Header and footer, Text and symbols. Each of these submenus has a set of tools that you shall use to perform small tasks in when working with your documents.

ICT in a business environment can be used for:

• 
  Recording Data,
  
• 
  Storing data,
  
• 
  Manipulating data and
  
• 
  Retrieving data
  

• 
  Administration- For Invoicing, Communication, Emailing.
  
• 
  Business, Finance and Accounting- for Business Plans, Financial forecasting, Auditing, Market Analysis, Research, Recording Transactions.
  
• 
  Communications- For email, instant messages, mobile phones.
  
• 
  Engineering and Creative Art- for 2D and 3D Drawing, Modelling, Simulation.
  
• 
  Wildlife and Tourism and Hospitality- Animal Tracking, Hotel booking, GIS.
  

Today’s business is very different from the traditional business environment. Figure shows the four main aspects that characterise the modern day business environment. These aspects are the nature of business, technology, customers and the market.

The nature of business

Technology

Three Spheres of Web Strategy

Figure 3a

When we talk of the web strategy we refer to how a business would deal with the issues that affect the way they appear to the outside world through their websites. Nowadays people know about an organisation mainly through visiting their website on the Internet. So, the business managers need to constantly update their information on these websites. The nature of your website and its content determine largely how your business will fare.

A good website should balance the three elements shown in figure 3a (community, technology and business)

Consider a website that focuses only on the community and the business. In this case the website takes into account the expectations of the community first and fuse them into their website. You realise that every business operates in a certain environment and serves a specific community. It is paramount to note that each community has its own norms and values that shape its people’s expectations from the business. So a wise business manager has to make a thorough investigation into these norms, values and expectations. On the other hand the business has to be understood in terms of its processes and procedures.

The website now has to reflect the community expectations and the business processes and procedures. As figure 3a shows, this type of website will be inefficient for the success of the business. The website needs to be hosted on the Internet hence technology tools are required.

A business that ignores the community and focuses on the business processes, operations and expectations taking into consideration the modern IT technology is likely to fail again. As indicated in figure 3a users will be frustrated and may not even come onto the website. In this case the business will eventually collapse. Clearly no business can survive when it does not recognise the norms, values and expectations of the community that it serves. So make sure that pictures, logos, icons and everything that you use on your business is in line with the community if you want your products to do well. Imagine someone with a UK background where an owl is considered a lucky bird comes to Zimbabwe and puts pictures of an owl on every page of the website as well as banners to advertise the products!!!!!!!!!!!!!!!!!!!!!!!!!!! Pakaipa pakaipa. People will run away. The reason is simply that an owl in Zimbabwe is associated with witchcraft. So take the people’s culture seriously when branding your products.

Another approach may be taking only the society and the technology seriously. Clearly this does not work because the business functions and processes themselves are left out which should be the main reason of existence. Only a fool will ignore the business since the result is monetisation issues where no transitioning will occur. Actually there will be no business to talk about.

Finally, the proper way of doing it is considering the community, the business and the technology equally and inculcates them into the website development and maintenance always. When this is adequately done we now talk of web strategy balance. This is the optimal way of running a business properly online.

Internet, Email and E-Commerce

The Internet connected every part of the globe. The globalisation of business resulted in us having the following

• 
  Global Market Place
  
• 
  E-Commerce
  
• 
  Market Performance
  
• 
  Price Comparison Sites
  

• 
  Messages can be sent to individuals and groups
  
• 
  Quick Information Transfer
  

Electronic commerce came also as a result of doing business on the Internet. The benefits that accrued to business following this include the following;

• 
  Shopping 24/7
  
• 
  Low Overheads
  
• 
  Global Market
  
• 
  E-Marketing
  

• 
  Speed- Quicker processing times save the business time and money. Transactions are processed on quicker on real-time
  
• 
  Accuracy- with the use of verification and validation, data can be inputted more accurately. This can help with decision making.
  
• 
  Data Handling- Can be inputted and manipulated anywhere on the market
  
• 
  User friendly- Easy to use
  
• 
  Capacity- Large quantity of data can be held with very little physical space
  

A computer network is a group of computers connected to each other electronically.

This means that the computers can "talk" to each other and that every computer in the network can send information to the others.

The components of a computer network include: a computer, the router, the gateway, the bridge networking device, the switch for networking and the hub. Most of these are data terminal equipment and components of networking that are tasked with receiving or generating data.

A virtual private Network (VPN) extends a private network across a public network, such as the Internet.

Definition of terms

• 
  A database is an organized collection of data.
  
• 
  A computer is a general purpose device that can be programmed to carry out a set of arithmetic or logical operations
  
• 
  A router is a device that forwards data packets between computer networks, creating an overlay internetwork.
  
• 
  A network switch (sometimes known as a switching hub) is a computer networking device that is used to connect devices together on a computer network.
  

• 
  It is the transformation of an organization’s processes to deliver additional customer value through the application of technologies, philosophies and computing paradigm of the new economy
  

• 
  Three primary processes are enhanced in e-business:
  
  1. 
     Production processes, which include procurement, ordering and replenishment of stocks; processing of payments; electronic links with suppliers; and production control processes, among others;
     
  2. 
     Customer-focused processes, which include promotional and marketing efforts, selling over the Internet, processing of customers’ purchase orders and payments, and customer support, among others; and
     
  3. 
     Internal management processes, which include employee services, training, internal information-sharing, video-conferencing, and recruiting.
     

• 
  The major different types of e-Business are:
  
  • 
    Business -to- business (B2B);
    
  • 
    Business to-consumer (B2C);
    
  • 
    Business -to- government (B2G);
    
  • 
    Consumer -to- consumer (C2C);
    
  • 
    Mobile commerce (m-commerce).
    

• 
  Content & User Experience
  
  • 
    Content Strategy
    
  • 
    User Experience (UX) & Design
    
  • 
    Information Architecture (IA)
    
  • 
    Usability & QA Testing
    
• 
  Application & Development
  
  • 
    Web development
    
  • 
    Data Warehousing & ETL
    
  • 
    Product data management
    
  • 
    Integration with business partners
    
  • 
    Operations (Order placement, order processing, & supply chain management)
    
• 
  E-Marketing & Demand Creation
  
  • 
    Direct Marketing
    
  • 
    Email Marketing
    
  • 
    Search Engine Marketing, Search Engine Optimisation, Online Advertising
    

• 
  Online Merchandising & Conversion
  
  • 
    Internal Site Search (searches performed on the website, not in a public search engine like Google)
    
  • 
    A/B & Multivariate Testing
    
  • 
    Online Merchandising
    
• 
  CRM, BI, & Analytics
  
  • 
    Customer Relationship Management & Database management
    
  • 
    Business Intelligence
    
  • 
    Competitive Intelligence and Web Analytics
    

• 
  Software are the instructions given to a computer in the form of a program.
  
• 
  Software is the set of programs, which are used for different purposes.
  
• 
  Software are all the programs used in a computer to perform certain tasks.
  

Software is divided into two broad categories:

1. 
   Systems software and
   
2. 
   Application software.
   

• 
  Systems software is the term used to describe programs that enable the computer to function, improve its performance and access the functionality of the hardware.
  
• 
  Function of systems software is the control of the operation of the computer.
  
• 
  Systems software provides the foundation for applications software.
  

Systems software is further subdivided into operating systems and utilities.

• 
  The operating system is the program that actually makes the computer operate.
  

• 
  It is the basic minimum software needed for a computer to be functional.
  
• 
  It constitutes the greater part of Systems software.
  
• 
  Its major function is to control the hardware
  

• 
  Boot-up the computer.
  

• Control input devices such as keyboards, mice and scanners.

• Control output devices such as the video display and printer.

Control the external ports: Ports are the external connections that enable peripheral devices to be connected to a computer. Common types of ports are serial, parallel, USB. Of these the USB ports are the most important.

• Provide the functionality for computers to be linked in a network.

• Provide the foundation for application software to be launched.

• Enable application software to access and use the hardware.

Utilities Software

Utilities Software are programs which either improve the functioning of the operating system or supply missing or additional functionality.

Examples: Windows Explorer (File/Folder Management), Windows Media Player,, WinZip, WinRAR for compressing files

Applications software

• 
  Application software is used in real-world tasks to solve user problems
  
• 
  Application software is used in real-world tasks to solve user problems
  

1. 
   Off the shelf
   

Software specially designed for a particular industry or organization E.g. Galileo/Worldspan (Travelling Agents) , ASCUDA for ZIMRA border clearance, POSware for supermarkets etc

• 
  The new releases of software products are called versions.
  
• 
  The versions use a numbering system such as
  

• 
  Software developers continually strive to improve the performance of their products and add new features.
  
• 
  Especially in a world of competing products, each developer needs to make their product perform better, have fewer problems and have more features.
  

Basically in two forms i.e.

1. 
   Proprietary software
   
2. 
   Open source software
   

• 
  Also called non-free software, is software with restrictions on using, copying and modifying as enforced by the proprietor(owner).
  
• 
  Restrictions on use, modification and copying is achieved by either legal or technical means and sometimes both.
  
• 
  Examples of proprietary software are Microsoft Windows, Microsoft Office, Norton Antivirus etc.,
  

• 
  Open source software (OSS) is computer software whose source code is available under a license that permits users to use, change, and improve the software, and to redistribute it in modified or unmodified form.
  
• 
  It is often developed in a public, collaborative manner.
  
• 
  Common OSS products are Linux, Netscape, Apache, etc.,
  

• 
  It is copyrighted software given away for free by the author.
  
• 
  You are unable to view the source code
  
• 
  Although it is available for free, the author retains the copyright, which means one cannot do anything with it that is not expressly allowed by the author.
  
• 
  Usually, the author allows people to use the software, but not sell it.
  
• 
  Examples: Adobe PDF, Google Talk, Yahoo Messenger
  

• 
  Freely distributed for a trial period
  
• 
  You can only enjoy a free trial of it for a short period e.g. 14 days after which you are required to pay for a license
  
• 
  The author usually requests that you pay a small fee if you want to use the program regularly.
  
• 
  By so doing, you become registered with the producer so that you can receive service assistance and updates.
  
• 
  You can copy shareware and pass it along to friends and colleagues, but they too are expected to pay a fee if they use the product.
  
• 
  Examples: Winzip
  

• 
  Thus, there are practically no packaging or advertising expenses.
  
• 
  Note that shareware differs from public-domain software in that shareware is copyrighted.
  
• 
  This means that you cannot sell a shareware product as your own.
  
• 
  Examples:
  

Software Piracy

• 
  Making illegal copies of copyrighted software
  
• 
  Why the fuss?
  
  • 
    Very easy to duplicate software
    
  • 
    Software company may lose hundreds of dollars per pirated copy
    
• 
  Prosecution
  
  • 
    Possible: Small-medium sized business who purchase a few copies and distribute to many users
    
  • 
    Impossible: Individual users who probably would not have purchased software on their own anyway
    

• 
  Software is copied onto CD-ROMS / DVD-ROMS
  
• 
  Package duplicates the original
  
• 
  Sold in flea markets or small stores
  
• 
  Cheaper price
  

• 
  Legitimate reasons
  
  • 
    Backup copy
    
  • 
    Copy to hard disk
    
• 
  Illegitimate reasons
  
  • 
    Obtain software without paying for it
    

• 
  Suites are a number of productivity packages bundled together. Examples:
  
  • 
    Microsoft Office has MS Word, Excel, Power point, Internet Explorer, Access etc
    
  • 
    Lotus SmartSuite
    
  • 
    Corel WordPerfect Office
    
  • 
    Sun StarOffice
    

• 
  Cost
  
• 
  Similar graphical user interface
  
• 
  Share common tools
  
• 
  Programs are designed to work together
  

• 
  Large size
  
• 
  Many features never used by many end users
  

1. 
   Describe the factors to consider when purchasing software.
   
2. 
   For each of the scenarios below, suggest the appropriate hardware and software needs:
   

1. 
   Airline reservation
   
2. 
   Biomedical imaging
   
3. 
   Lecture theatre
   
4. 
   Diamond mining
   

1. 
   A set of computer instructions
   
2. 
   Deliberately created
   
3. 
   That propagates
   
4. 
   And does unwanted things.
   

1. 
   Cannot exist in a viable form, apart from another (usually legitimate) program.
   
2. 
   Propagates when the host program is executed.
   
3. 
   Has an incubation period, during which no damage is done.
   
4. 
   After incubation period, begins to manifest its behavior.
   

1. 
   Sudden or periodic slowing of programs.
   
2. 
   Unexplained change in the size of any program.
   
   • 
     Files with extension .EXE.
     
   • 
     Files with extension .COM.
     
   • 
     Files with extension .BAT.
     
   • 
     Files with extension .SYS.
     
   • 
     Files with extension .OVL.
     

("Explanations" would be, for example, a new version of DOS, or re-installing a program with different options.)

3. 
   Unusual behavior of the computer, especially during a program which you have been running regularly with no problems.
   
4. 
   Failure of any program (such as a word processor) to install correctly from its distribution disks.
   

1. 
   Trojan horse: a standalone program which does its damage immediately, while you are running it for another purpose (usually a game!).
   
2. 
   Bomb: a standalone program (like a Trojan horse) whose only effect is to destroy some part of your system (programs, data) but does not pretend to be another program while it runs.
   
3. 
   Bug: a legitimate program with some logic error which causes accidental damage to your system even though everything was done according to the manual.
   
4. 
   User error: a human error (which the human may deny!) which causes loss of data or programs, or damage to hardware, due to accident or entry of incorrect commands.
   

1. 
   Formats hard drive, destroying all data ("Dark Avenger").
   
2. 
   Causes random change in typed characters ("Teatime" virus).
   
3. 
   Presents a political or (false) advertising message every few times ("Stoned" virus: Legalize Marijuana).
   
4. 
   Causes computer to act as though a monitor or disk drive is going bad ("Jerusalem-B" virus).
   

1. 
   In the "boot" sector of any floppy disk. This is a small program which runs whenever the computer is "booted" from the diskette, whether or not the diskette is "bootable." (This is the tiny program which puts the message "Non-system disk or disk error" on the screen if the disk is not bootable!)
   
2. 
   Attached to any program: shareware, commercial or public domain.
   
3. 
   Embedded in the hidden system files IO.SYS and MSDOS.SYS on the boot disk or drive.
   
4. 
   Same as #2, but pay SPECIAL ATTENTION to the file COMMAND.COM on the boot disk or drive.
   
5. 
   The "partition table" on a hard drive. (This DOES contain executable information, since it is attached to the "Master Boot Record" which is consulted at boot-up to determine whether to boot DOS, OS/2, UNIX, etc.)
   

1. 
   Trading, copying or pirating software on diskettes without knowing the source.
   
2. 
   Software salesmen giving demos on your computer from their diskettes.
   
3. 
   Computer repair personnel using diagnostic disks.
   
4. 
   Computer user groups and bulletin boards (BBS's). NOTE: #2 & #3 account for over 80% of all infections at business sites! #1 accounts for nearly all others, #4 LESS THAN 5%.
   

1. 
   Every few times the computer is booted up
   
2. 
   On a certain day of the year
   
3. 
   On a certain day of the week ("Sunday" virus).
   
4. 
   On a certain day of the month ("Friday the 13th", "Saturday the 14th" viruses).
   
5. 
   Every day EXCEPT one ("Israeli" or "Suriv03" virus, every day except Friday the 13th.)
   
6. 
   On a certain date only. (Jan. 1, 2000 "Century" will activate, write zeroes to all connected disks, effectively destroying all data and programs, destroying all directories, file allocation tables, boot records and partition tables, possibly causing the disk to have to be returned to the dealer for repair. Finally, a message is presented to the user, "Welcome to the 21st Century.")
   
7. 
   A certain period after infection ("Plastique" virus, one week).
   
8. 
   After infecting a certain number of files ("MIX/1" virus, six files).
   
9. 
   After a certain number of keystrokes ("Devil's Dance" virus, 2000 keystrokes; after 5000 destroys hard disk data and prints characteristic "Devil's Dance" message).
   
10. 
    At a particular time of day ("Teatime" virus, between 3:10 and 3:13 PM, trashes every 11th keystroke.)
    
11. 
    Any combination of the above, plus anything you can probably think of!
    

• 
  Boot-sector viruses. Can NOT be transmitted from BBS's at all. Transmitted by floppy or tape cartridge (rare). Boot- up must be attempted from infected disk. Remains memory- resident during warm boot, infects boot sector of all other disks in system including hard and floppy disks.
  
• 
  Program viruses. May be transmitted by distribution of infected programs via floppy, BBS or network. Some infect ONLY COMMAND.COM; others avoid infecting COMMAND.COM, to avoid detection.
  

• 
  DOS. Greatest variety of viruses due to widespread use.
  
• 
  Amiga-DOS. Restricted to Commodore Amiga.
  
• 
  Macintosh. Restricted to Macintosh computers. NOTE: Amiga(TM) and Macintosh(TM) computers often have a DOS emulation mode. In this mode, some (but not all) DOS viruses can damage them as well.
  
• 
  OS/2. Relatively immune to viruses so far, due to rarity of systems. Most DOS viruses are rendered harmless by OS/2, although some may still survive since OS/2 can also run DOS programs.
  
• 
  UNIX. These viruses are relatively rare, but some have the potential of migrating to PC's running UNIX clones such as XENIX. Similar remarks apply to Amigas and Macintoshes running A/UX or other UNIX clones.
  
• 
  VMS, MVS, etc. (Minicomputers & mainframes). A few viruses spread over networks. More commonly affected by worms (RTM Internet worm, e.g.), logic bombs via e-mail, etc.
  

• 
  Many computers in close proximity. "Proximity" may not be physical distance between computers, but between computer owners in the same class or job.
  
• 
  Frequent exchange of susceptible software.
  
• 
  Long incubation period of virus.
  
• 
  Proportionately few "immune" individuals in the community, i.e. those using anti-viral software.
  
• 
  Use of software brought from home, where "the kids" could bring home viruses from school, etc.
  

Remove any of the conditions above.

• 
  Isolate computers. This is seldom practical! But you can set aside one computer in an organization on which to try out disks and software before releasing disks for general use.
  
• 
  Don't be hasty to try every new program that comes down the pike.
  
• 
  Use the computer set aside in #1 to set future dates and see if anything happens.
  
• 
  Use anti-viral software on ALL computers, and keep it updated regularly. (The few users who don't use the software will be protected by "herd immunity" which is well known in disease control.)
  
• 
  Disallow use of any software not purchased by and for the corporation, or disinfected as in #1 and #3.
  

The development of electronic computers can be divided into five generations depending upon the technologies used. A computer generation is born when there is a departure in technology.