Chapter 7. Output Devices

Output Devices

An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) to the outside world.
In computing, input/output, or I/O, refers to the communication between an information processing system (such as a computer), and the outside world. Inputs are the signals or data sent to the system, and outputs are the signals or data sent by the system to the outside.
The most common input devices used by the computer are the keyboard and mouse. The keyboard allows the entry of textual information while the mouse allows the selection of a point on the screen by moving a screen cursor to the point and pressing a mouse button. The most common outputs are monitors and speakers.
Visual display unit
A visual display unit (also called VDU, monitor, or screen) offers a two-dimensional visual presentation of information.
Scanners- Scanners allow you to transfer pictures and photographs to your computer. A scanner 'scans' the image from the top to the bottom, one line at a time and transfers it to the computer as a series of bits or a bitmap. You can then take that image and use it in a paint program, send it out as a fax or print it. With optional Optical Character Recognition (OCR) software you can convert printed documents such as newspaper articles to text that can be used in your word processor. Most scanners use TWAIN software that makes the scanner accessable by other software applications.
Digital cameras allow you to take digital photographs. The images are stored on a memory chip or disk that can be transferred to your computer. Some cameras can also capture sound and video.

Monitors and Displays
The monitor shows information on the screen when you type. This is called outputting information. When the computer needs more information it will display a message on the screen, usually through a dialog box. Monitors come in many types and sizes from the simple monochrome (one colour) screen to full colour screens.
Most desktop computers use a monitor with a cathode tube and most notebooks use a liquid crystal display (LCD) monitor.

Speaker
A speaker can be used for various sounds meant to alert the user, as well as music and spoken text.
Printers - The printer takes the information on your screen and transfers it to paper or a hard copy. There are many different types of printers with various levels of quality. The three basic types of printer are; dot matrix, inkjet, and laser.
Dot matrix printers work like a typewriter transferring ink from a ribbon to paper with a series or 'matrix' of tiny pins.
Ink jet printers work like dot matrix printers but fires a stream of ink from a cartridge directly onto the paper.
Laser printers use the same technology as a photocopier using heat to transfer toner onto paper.
Modem - A modem is used to translate information transferred through telephone lines or cable.
The term stands for modulate and demodulate which changes the signal from digital, which computers use, to analog, which telephones use and then back again. A high speed connection also requires a modem but because the information is transferred digitally it isn't required to change the signal from digital to analog but is used to create the connection between your computer and the computer you are connecting with.
Modems are measured by the speed that the information is transferred. The measuring tool is called the baud rate. Originally modems worked at speeds below 2400 baud but today analog speeds of 56,000 are common. Cable, wireless or digital subscriber lines (DSL) modems can transfer information much faster with rates of 300,000 baud and up.

Chapter 8. Operating System

Operating System

All computers need some sort of Operating System (OS). The majority of modern home computers use some form of Microsoft's operating systems. The original Microsoft operating system was called DOS (Disk Operating System) though most computers use Windows. Windows comes in various versions beginning with version 3.x then 95, 98, ME and currently XP. A few computers use IBM's O/S2. Apple's Mac use their own operating system beginning with OS 1 though most modern Macs use version 8.x or 9.x. Apple's latest version is OS 10.1.x. In the past large companies and institutions would have an operating system design exclusively for them but as the commercial operating systems become more sophisticated the benefits of this practice is becoming less apparent. Some computer professionals, Internet Service Providers (ISP) and mainframe computer users use an operating system such as UNIX (or a variant such as Linux), Windows NT or 2000 (Win2k) or one of the other network or server based operating systems.
There are many smaller operating systems out there. The problem is that software is currently being developed only for the main operating systems and only the newest versions of these OS. Many older computers with unique operating systems have lots of software already developed for them but there is very little new software being developed for the older computers. The older proprietary operating systems are less likely to offer technical support than the more modern operating systems.
The operating system controls the input and output or directs the flow of information to and from the CPU. Much of this is done automatically by the system but it is possible to modify and control your system if you need to.
When you turn your computer on it first needs to load the operating system sometimes referred to a booting up. Basically the computer starts from scratch every time you turn the power on.
It checks all its components and will usually display a message if there is a problem. Loading the system is usually automatic.
Once the system is loaded the user can start the application or program that they are going to use.
Most computer users will run Microsoft Windows, Mac OS or Linux as their operating system. These OS are Graphic User Interface (GUI) which allows the user to control or run the computer using a Mouse and Icons. The user simply moves the mouse on a flat surface, rolls the trackball, or moves their hand over the touchpad to control a pointer. They then choose the option they want by pressing a button or touching the pad.
Without a GUI the user controls the computer using the keys on the keyboard. This is referred to as a Command Line Interface (CLI)

Chapter 9. Computer Viruses

Computer Viruses

A virus is a program designed by a computer programmer (malicious hacker) to do a certain unwanted function. The virus program can be simply annoying like displaying a happy face on the user's screen at a certain time and date. It can also be very destructive and damage your computer's programs and files causing the computer to stop working.
The reason why hackers create viruses are open for speculation. The most quoted reason is simply to see if it can be done. Other reasons are Ludite based "smash the machine" motivations, antiestablishment/anti-corporate actions, criminal intent, and various others that range into the "conspiracy theory" realm.
Viruses take two basic forms
One is a boot sector viruses which infect the section of a disk that is first read by the computer. This type of virus infects the boot or master section of any disks that it comes in contact with. The second is a program virus that infects other programs when the infected program is run or executed. Some viruses infect both and others change themselves (polymorphic) depending on the programs they encounter.
Though viruses do not damage computer hardware there have been attempts to create programs that will do things like run the hard drive until it fails or lodge itself in the computer's clock (which has a rechargeable battery) allowing it to remain active even months after the computer has been unplugged. Other viruses affect certain microchips (BIOS chip for instance). These microchips need to be modified under normal computer use but the virus program can produce changes which cause them to fail. Other viruses will affect the characters or images displayed on the screen which may give the impression of monitor failure.
Viruses can cause a great deal of damage to the computers it infects and can cost a lot of time and money to correct it.
Computer viruses have been around for a long time, even before computers became widely used and they will likely remain with us forever. For that reason computer users will always need ways to protect themselves from virus programs. The main, common feature of a virus is that it is contagious! Their sole purpose is to spread and infect other computers.
A computer gets a virus from an infected file.
The virus might attach themselves to a game, a program (both shareware and commercial) or a file downloaded from a bulletin board or the Internet.
You cannot get a virus from a plain email message or from a simple text file! That is because the virus needs to be 'run' or executed before it can take effect. This usually happens when the user tries to open an infected program, accesses an infected disk or opens a file with an infected macro or script attached to it. A plain email message is made up of text which does not execute or run when opened.
Modern email programs provide the ability to allow users to format email messages with HTML and attach scripts to them for various purposes and it is possible for a malicious hacker to attempt to spread a virus by building a virus script into an HTML type of email message.
When you are accepting software or scripts on Internet sites or reading mail from unknown senders it is best not to run a program from that site or sender without checking it with an anti-virus program first.
Protect yourself
You can take safeguards against virus infection. The first thing is to get an anti-virus program. Most reputable companies that create virus protection programs release an evaluation copy that a Internet user can download for free and use for a certain amount of time. This anti-virus program will be able to check your computer for viruses and repair damage or delete files that are infected with viruses. You may have to replace infected files that cannot be repaired.
The second thing you can do is purchase a copy of the program. The reason for this is that viruses are constantly being created. When you purchase an anti-virus program you are also purchasing periodical updates which keep your anti-virus program up-to-date and able to deal with new viruses as they are encountered. Commercial virus programs also allow the user to customize when and how the program will check the computer for viruses. You will need to renew this updating service periodically.
If you find that your computer has been infected with a virus use an anti-virus program to clean your computer and make sure to check all the disks that you use. This includes all the hard drives on your computer(s) and all your floppy disks and CDs as well as any media that you save information on. Remember that the virus can easily re-infect your computer from one infected file!
If you have to reload your computer programs, use the original program disks. You may want to check your original disks before reinstalling the software. If your original disks are infected contact the distributor to get replacements.
Always take the time to ensure that your computer is properly protected. Spending money on a good virus checking program could save you hundreds of dollars and lots of time later.
A discussion of viruses would not be complete without mentioning hoaxes. Malicious people without programming skills will send out fake virus warnings causing people to take unnecessary measures which often cause your computer harm. One example tries to get the unsuspecting computer user to delete an important system file by warning them that it is a virus. A legitimate virus warning will provide a link to a website operated by an anti-virus company with more information about that virus. Don't forward a virus warning until you have check out whether it is legitimate.

Chapter 10.Networks

Networks

Most people working in office with more than a couple of computers will be using some form of network. As networks become easier to setup and maintain more home users are also setting up networks to share resource such as disk space, printers, Internet connections and access to software.
A network is basically two or more computers connected through a cable or wire which share resources. Network software controls how the computers communicate.
There are dozens of different types of networks which are impossible to cover in an introduction article. This article focuses on home and small business networks using some version of the Window operating system.
To connect computers each of the computers needs a network card with a connection that allows a cable to be connected to it. Computers can be connected directly through a bi-directional cable or through an other piece of hardware called a hub. The hub then connects all the computers in your local network together. Both solutions cost about the same but a hub allows more than two computers to connect. A hub can also be used to connect two local area networks together to create a wide area network.
Some form of network software is required. This network protocol software is installed through the network preferences. NetBIOS was commonly used though recently a secure TCP/IP protocol has been developed. The network protocol determines how computers become part of the network and how they are recognized. The network must have a name and you can use some creativity at this point. Each computer must also have a unique name that other computers on the network can access them with.
If all goes well this is all you need but often there will be a conflict that can be resolved by establishing exactly how the computer will communicate. To solve these types of conflict your network needs a set DNS server address and each computer in the network needs to be assigned a unique IP address. The addresses usually are in the range of 192.168.x.x where x means any number between 0 and 255. Once these numbers have been entered your network should be functioning with each computer able to see the other computers on the network.
You must also decide which resources you want to share. You may want to make a disk or folder available, a printer or tape backup system so that everyone can use it. You may also want to have parts of the network that are either not accessible or accessible only through a password. File and print sharing must be enable on the computer that will share it's resources or host computer and they determine how they are accessed by other computers or clients.
A computer with an Internet connection can also share that connection with other computers on the network but you should check with your ISP what their policy on sharing Internet connections is. Sharing an Internet connection also raises some serious security issues. Many cable high speed Internet connections use the Network Neighborhood settings to create the Internet connection and connecting your home or office network to this existing system can cause problems. Though you may want to allow a computer in another room of the house to access files or run programs on your computer you probably don't want the kid down the block to have that same access.
Security on networks begin with passwords. Everyone who wishes to access the network must logon with a username and password. If someone cancels the password challenge they will be able to access the files and programs on that individual computer but can't access any of the network resources. Specific passwords for important folders or disks can also be set or access to folders or disks can be forbidden.
Unlike server/client networks where the server must be running before the computers can communicate the peer-to-peer network that comes packaged with Windows allow any computers that are turned on to communicate with other. Other computers in the network become accessible as user turn them on.
Networks can also be open to remote secure access through a virtual private network. A VPN allows a computer to connect to a computer or network through the Internet.