Page 1 GENERAL THEORY NOTES

SECTION 1 OF YOUR EXAM PAPER WILL ASK YOU TO ANSWER 10 QUESTIONS ON GENERAL THEORY. THIS SECTION IS WORTH 80 M.

GENERAL THEORY NOTES

(If you do not understand any words, please refer to your WORDBANK and EXPLANATIONS.)

There are 4 main areas to cover:(This handout will cover Theory on each of these 4 Main Areas)

1. HARDWARE2. SOFTWARE3. NETWORKS, CONNECTIVITY, COMMUNICATION & THE INTERNET.4. USE/MISUSE AND CARE OF COMPUTERS

Page 2 GENERAL THEORY NOTESHARDWARE

1. Hardware : is any physical part of a computer (it is a group of machines)2. Hardware is made up of : (a) The CPU and Main Memory

(b) Input Devices (c) Output Devices (d) Storage Devices

3. Main Memory: Stores Programmes and Data for processing.4. CPU: Controls all operations/jobs, it reads all data into the main memory from an Input Device; it

processes the data according to instructions and produces information using an output device. (So it reads data, changes it and produces information for you to use).It is like the Brain of the Computer.

5. Input Device : These Devices read incoming Data and pass it on to the CPU. Examples are: Keyboard, Disk Drive, Scanner, Bar Code Reader, Voice Recognition, and Digital Camera.

6. Output Devices : these Accept information from the CPU and display the results for the user. Examples are: Printer, Monitor.

7. Storage Devices : these keep information and instructions in the Computer so that they can be used again. Examples are: CD’s, Floppy Disks, Hard Drive.

8. Looking at Input Devices in More Detail:

Mouse: Used to select text, insert text or an icon on a page by clicking and dragging. The cursor changes shape depending on the task. E.g. arrow, beam, egg timer shapes.

Keyboard: Used to type words on the page. The most common type is a QWERTY keyboard; it is laid out in an ‘unfriendly’ manner, in order to slow down speed typists. The most commonly used letters are spaced out to avoid them sticking.

Bar Code Reader/Wand Reader or Scanner:

They read or scan the zebra like bars that you see on most products. The black and white bars are different widths and together they form a code called a UPC or Universal Product Code. They are used in supermarkets where the bar code on the item is scanned and the products information is read, e.g. its price. This scanner is often connected to a POS or point of sale terminal called an electronic cash register. The wand reader is a hand held type that can be used for scanning items e.g. a Library book.

Page 3 GENERAL THEORY NOTESPoint of Sale Terminal:

They are used to collect information on a product by scanning the bar code. They record and store information e.g. its price, country of origin, and they record the sale and produce a slip/receipt for the customer.

Digitiser: Used for drawing illustrations or creating graphics/pictures on a page.Camera/Tape Recorder:

Used to input voice or visual pictures on to your computer.

VDE/Voice Data Entry:

It can accept human speech and convert it to the spoken word onto your screen.

OCR/Optical Character Reader (optical scanner):

They are devices that scan the document and turn it into readable form on your screen. It can be text, graphics or photo material. The results can be cut, copied and pasted, then saved to a disk. Books, for example can be entered onto the computer without the need for keying in text. The scanner changes the text from paper onto your screen

MICR/Magnetic Ink Character Reader:

They are used when documents, contain magnetic digits that contain information. E.g. flat numbers on the bottom of a bank cheque that represents information about a customer’s account.

OMR/Optical Mark Recognition/Reader:

The computer will pick up marks, e.g. pencil marks on a sheet to collect information. E.g. Pencil marks on a score sheet.

Touch screen: It is a special screen which allows you to carry out a task by touching on the screen. E.g. a Point of Information (POI) screen in a shopping centre, you can touch it to find out information about different levels/floors.

Light Pen or Stylus: You can use a special pen to touch the ‘touch screen’. It can be used to highlight and select items. You can also make hand written entries.

Mouse Keyboard Bar Code/Wand Reader Point of Sale Terminal

Plotter Camera Tape Recorder Voice Data Entry Optical Scanner

Magnetic Ink Character Reader Optical Mark Reader Touch Screen Stylus/Light Pen

Page 4 GENERAL THEORY NOTES

9. Looking at Output Devices in More Detail:

Monitor/VDU Or Visual Display Unit:

This is the screen that you look at; it contains a soft copy of your information. (The copy of your work on the computer, rather than a hard copy, which is the copy that you have printed out on paper). As you key in text, it appears on the Monitor for you to see. There are different types of monitors; one is the CRT or Cathode Ray Tube. They are similar to the picture tube in your TV. They shoot little dots across the screen that light up tiny points that glow for a short period of time. Every Letter/Character that you see on the screen is made of many of these lights or points called Pixels. The more Pixels that makes up a letter or text then the better the image or resolution.

Flat Screen Technology’s:

Portable computers like laptops, notebooks, and PDA’s or personal digital assistants can have high resolution screens. The most common is the LCD or Liquid Crystal Display.

Printer: They are used to produce a hard copy of your information. There are many types; the two main types are Impact and Non Impact. The speed at which pages print, refers to PPM or pages per minute. The DPI or dots per inch refers to the quality of print. When printing you should always check your print preview first, as ‘what you see in the print preview is what you get when you actually print, hence the term : ‘what you see, is what you get’ – WYSIWYG.

Non-Impact Printer:

These printers cannot make carbon copies. Examples are: Thermal Printer: they respond to heat and create letters on special paper. They are slower than Ink-Jet and the paper is expensive. Ink Jet Printer: they shoot tiny dots of ink onto paper. Laser Printer; they beam whole pages at a time onto a drum, the paper then passes over the drum and picks up the image or text.

Impact printer: They are slower, noisier and often breakdown, they are more inexpensive. Examples are:. A Dot Matrix: it creates characters from pins. The pins strike against a carbon ribbon to print on paper. Character Printer: it uses a daisywheel to print characters/letters. They print letters from a flat disk that has metal letters attached. It is slow, but is the most common type of Impact Printer.

Plotter: They are printing devices that produce a high quality image for drawings. Audio response: Used to provide verbal responses using a voice simulator or pre-recorded messages, e.g. Directory

assistance.Microfiche/film: When large amounts of information need to be stored, miniature copies of documents are kept on

microfilm. E.g. Newspapers for the past 100 years.Speaker Sends out Audio/SoundDigital Projector

Displays the Monitors Image on a Large Screen/Wall

Monitor Flat Screen Monitor Thermal Printer Ink Jet printer Laser Printer Dot Matrix Printer

Character Printer Plotter Audio Response Microfilm Reader Speaker Digital Projector

Page 5 GENERAL THEORY NOTES

10. Looking at Storage Devices and Memory in More Detail:

STORAGE DEVICESStorage: It is very important to store your information carefully so that you do not lose it and know where

to find it. You may store information directly onto your computer or on different types of storage devices e.g. Floppy Disk, CD or USB Key. It is important to store back up’s also; in case one copy becomes unusable. (a back up is like a second copy of your information).

Magnetic Disks and Disk Drives:

This is often called a disk; information is stored in rings, called tracks.

Floppy Disk: It stores programs and files, e.g. 3 ½ Floppy that is called the A drive. Inside is a thin disk and has a plastic case around it. It contains information in rings called tracks. Disks often have to be formatted, this means erasing all of its information in order to make it work. this can be done by right clicking on the disk icon and clicking on format.

Disk cartridge: It can store more information than a floppy disk, but it is not portable.Tape Drive: Still used in certain workplaces to store large amounts of information, but disks are faster and

can store more information. CDROM: (Optical)

It is a silver plate, used to play audio and store information. They can store the same amount of information as 100 floppy disks. E.g. the Entire phone directory of the USA is contained on one CD ROM.

WORM CD’S (Optical)

Write Once, Read Many times. They store large amounts of information, you can copy information to it once, you cannot change this information, but you can read/use it whenever you like.

ERASABLE CD’S: (Optical)

You can copy information to it many times, and read information whenever you like.

USB key: Often called a pen drive/flash drive/memory stick or USB stick. It is inserted into the USB on your computer and information can be stored on it as a back up. It is portable.

Hard Disk: This is the permanent disk inside the Tower of your computer that you can store information to, called the C Drive. It is not portable.

MEMORY:Memory: This is the space the computer has to store information.Byte: This is a letter or a symbol. A Kilobyte (K) is 1024 Bytes. A Megabyte (Mb) is 1 million Bytes.

A Gigabyte (Gb) is 1 Billion bytes.Speed: The speed of this memory is measured in nanoseconds or billionths of a second. We use the

symbol MHz or megahertz when describing speed. MIPS: Millions of Instructions per second, or the speed and memory size together.Volatile/Non-Volatile:

The main memory is volatile, that means if the computer is switched off, it will be lost. So information should always be stored on a disk, or the hard drive, so that it is safe and non volatile.

RAM/random Access Memory:

This memory stores programmes and it stores information or small commands while you are working. It is volatile. E.g. if you are typing and you decide to cut and paste. You may right click, and cut, go to another spot on the page and paste; the computer knows to do this as it has stored it in its memory. But if you switched off the computer before you clicked paste, it would not remember to paste this text when you switch it back on. It’s like a short term memory.

ROM/Read only Memory:

These are permanent instructions in the computer. When you turn off the computer it will still know what to do and how to do it when you turn it on. For Example: when you turn on a computer it knows to check is the printer connected, it knows that the ‘enter’ key on a keyboard will skip a line. So it is like a computers long term memory, it won’t ever forget how to do it.

Page 6 GENERAL THEORY NOTESStorage Capacity: This is the amount of information that a computer can hold.Backup: This means to create another safe copy in case one gets destroyed, by a virus (bug on a file)

SOFTWARE1. Software : Before a computer or any hardware can actually read data, process/change it, and produce

information for you, it needs a set of instructions. These instructions are in the Software.2. Types: So the software is like a ‘set if instructions’ put together that helps the computer carry out

different jobs. There are 2 main types of Software. They are: Operating Systems Software and Applications/Programme Software.

3. Operating Systems Software or OS: This software supervises the overall operations of a computer. Examples are: IBM use DOS or Disk Operating Software, and Apple, Macintosh, Dell, and Gateway use Windows Operating Software. Windows is what you are using and you can carry out a job by clicking on a Graphic/Picture Symbol or an ICON by clicking on them. E.g. a Scissors will cut text.

Sofware Programs Operating Systems ICONS

Magnetic Disk Disk Drive Floppy Disk Disk Cartridge Tape Drive CD-ROM

WORM CD Erasable CD USB Key USB Cable Hard Disk Memory Board

RAM ROM Storage Capacity

Page 7 GENERAL THEORY NOTES4. Compatible/incompatible Disks : A Disk that is prepared for one OS may not work on another OS. For

Example: Word Perfect for Windows my not work in Macintosh, you may have to get the Macintosh version. In this case they are incompatible or, they cannot be used together. If you can use a disk in two different Operating Systems, then they are compatible.

5. Applications Software (Program Software): These are programs that you can simply buy off the shelf from a retailer/shop like PC world. In some cases a company may want to use specific programs, in that case they can get the programme specially designed; E.g. Schools uses a Facility Programme to keep school records, Accountants use a Payroll Programme to do their accounts.

NETWORKS, CONNECTIVITY & COMMUNICATION1. Network : this is the idea that computer resources in an area can be shared; it is shared by an

Integrated Computer System (integrated/interconnected). For Example: Your computer room in school may have 20 computers but only 1 printer, if for example 10 of these computers can send documents to the 1 printer to print, then they are sharing the resource or sharing the 1 printer. It makes more sense to share an expensive resource like a printer, rather than to have 1 printer attached to each computer.

2. Information such as files can also be shared: using a network. A large computer called a server is used to help share files and information on the network for many people to use.

3. there are 2 types of Networks: LAN and WAN.4. WAN: This network is used to transfer and share information over a great distance, for example, from

one country to another country.5. LAN: A Local Area Network is used to transfer and share information and resources when computers

are close to one another. For Example, in a LAN the network may connect devices within a room or building.

RING STAR BUSCommonly used and they use a Server/Host. All computers/Node are connected in a loop.

All devices use a computer/Node and Server/Host, but not necessarily each other.

Computers/Nodes share the same bus or channel for transmitting to other computers/nodes or Servers/hosts.

Messages pass from Node to Node before it reaches its destination.

If one node is down, it is just by passed.

Nodes can access a Host as well as each other.

6. Connectivity: this is the linking of all equipment together, such as phones, faxes, computers etc..Ring Network Star Network Bus Network

Page 8 GENERAL THEORY NOTES7. An Example of Connectivity: Telephone lines move wave signals called analogue signals. However if

a Modem (modulator-Demodulator) is used, it can change digital signals (from a computer) into wave/analogue signals so that information can be sent over phone lines.

8. Communication: in order for this information to be sent, it needs to go through a suitable communication channel, or a cable. There are 3 main types of communication channels:

Twisted pair Cable Coaxial Cable Fibre OpticCost Cheapest More Expensive Most ExpensiveSpeed Slowest Higher Speed Highest SpeedQuality Bundles of Pairs of Copper

Wires, twisted to give good strength.

Low Error Rate. Very Good Quality.

Low Error Rate. very Good Quality.

Diagram

9. The Internet: allows you to connect with 1000’s of Networks worldwide. For example: you can access thousands of databases including, newspapers, journals, magazines, Universities, government agencies, businesses. An ISP or and Internet Service Provider will provide the customer with access to the internet, e.g. Eircom or NTL. Some use a dial up connection called an ISDN Line or Integrated Systems Digital Network. Dial up lines are becoming less common, as they are slower. The World Wide Web or WWW helps you to connect with any web page; you can type in an address in the top address bar called the URL or Universal Resource Locator. HTTP or Hyper Text Transfer Protocol will help you to search in this address bar. HTML or Hyper Text Mark up Language is the Language the internet often uses to carry out commands. A hyperlink is a blue link that connects you to another page. A search engine e.g. Google or Yahoo will help you to search for something by typing in words instead of a full address.10. Video Conferencing: this allows full motion video and sound to be transmitted over telephone lines. The sound is captured by microphones, it is sent to the listener at a high speed.

Page 9 GENERAL THEORY NOTESUSE/MISUSE AND CARE OF COMPUTERS:

Health and Safety relating to your Work Area1. Ergonomics : This refers to any Health and Safety issues relating to PC Use. For Example:2. In your work area: To Reduce Screen Glare, place a screen over your monitor. To reduce sound

pollution in your office, place sound absorbing materials on furniture, walls, ceilings and floors. To reduce sun Glare, place blinds on window.

3. To prevent discomfort and permanent injury, create an ergonomically designed workstation/Desk Area, for Example:

(a) Your arm angle in keyboarding should be 15-30 Degrees below your line of sight(b) The Screen should be 3-4 times brighter than the room, to avoid eye strain.(c) Your fingers should be no higher than 10 degrees higher than your elbow. (d) Your forearms should be horizontal, your lower back should have support, you should have an adjustable chair, and your feet should be flat on the floor.(e) Your Desktop should be 29 inches from the floor, your monitor.(f) You should have a wrist rest to prevent Repetitive Strain Injury.(g) You should have a mix on screen and non screen based tasks or take breaks from the computer.

Care of Floppy Diskettes:1. Any disk can become ‘corrupt’ and will not work if not looked after properly, so you should always

keep a back up, or a second copy of the information somewhere else.2. Keep the Disk safe in a box or container. 3. When writing on the Label, do so, before you place the label on the disk, as it could damage it.

ADVANTAGES OF COMPUTING DISADVANTAGES OF COMPUTING1. Fast: high Speed of getting Information. 1. Cost : may be Expensive to start with.2. Accurate: It is almost 100% accurate/correct. 2. Errors: There may be Mistakes inside the

programme.3. Compact Storage : No filing Cabinets needed all info on

PC.3. Training Costs : Training Staff may be time

consuming and expensive.4. Presentation : Clear, Neat Work. 4. Virus : If a computer gets a Virus, you may loose

everything.

Page 10 GENERAL THEORY NOTES