ContentsSection 1: Fundamentals of Hardware and Software...............................................................................1

Objective 1.1: Describe a general-purpose computer system.................................................................1

Objective 1.2: Explain the functions of the major hardware components of a computer system...........2

Objective 1.3: Outline the functions and uses of primary storage devices..............................................4

Objective 1.4: Manipulate units of storage.............................................................................................5

Objective 1.5: Compare the types of secondary storage media w.r.t. portability, speed and capacity.. .6

Objective 1.6: Use terms associated with storage devices......................................................................6

Objective 1.7: Explain the uses of various input devices and media......................................................15

Objective 1.8: State the types and functions of output devices............................................................20

Objective 1.9: Describe how data are stored and manipulated within the computer...........................25

Objective 1.10: Interpret the hardware specifications of a computer system.......................................33

Objective 1.11: Distinguish between system programs and application programs...............................35

Objective 1.12: Explain the functions of the Operating Systems...........................................................38

Objective 1.13: Distinguish among multitasking, multiprocessing and multiprogramming...................38

Objective 1.14: Explain the different types of processing modes..........................................................39

Objective 1.15: Distinguish between types of user interface................................................................40

Section 1: Fundamentals of Hardware and Software

Objective 1.1: Describe a general-purpose computer system.

Content: Major functions of systems: input, processing, output, storage

Notes: The major functions of a general-purpose system

The major functions of a general-purpose system are:

Input: involves obtaining data for processing

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Processing: involves the manipulation of data to produce information. Manipulation means multiplying, adding, subtracting, dividing, sorting etc.

Output: involves sending information to users. Storage: involves keeping the data on electronic storage.

Objective 1.2: Explain the functions of the major hardware components of a computer system.

Content: CPU, CU, ALU; main memory, secondary storage, input and output devices

Notes: The major hardware components of a computer system

The major hardware components of a computer system are shown in the diagram below.

Central Processing Unit (CPU)The CPU is also called the processor. It takes raw data, follows a set of instructions (programs) and converts it into information. The CPU consists of two smaller units known as the control unit (CU) and the arithmetic and logic unit (ALU).

Control Unit (CU)This is the main part of the CPU. It directs and coordinates all activities within the CPU. It determines the sequence in which instructions are executed. The CU executes an instruction by performing the following steps:

2

CPU

CU

ALU

Main Memory

Output devicesInput devices

Secondary Storage

1. Fetching the instructions from memory2. Decoding the instructions3. Fetching the data required by the instructions from memory4. Sending the data and instructions to the ALU for processing5. Sending the data to memory after processing

Arithmetic and Logic Unit (ALU)The ALU performs all the arithmetic and logic functions in a computer. The arithmetic operations include addition (+), subtraction (-), multiplication (*) and division (/).

The logic functions are comparisons, such as

1. Equal to (=)2. Not equal to (≠)3. Less than (<)4. Greater than (>)5. Less than or equal to (<=)

6. Greater than or equal to (>=)7. AND8. OR9. NOT

3

Main MemoryMain memory is also called computer memory, immediate access storage (IMAS/IAS) or primary storage. This unit of memory is directly accessible to the CPU. It holds data and instructions that the computer is processing at the time.

Secondary Storage Secondary storage is also called auxiliary storage, backing storage or disk storage. These devices are used to store data and instructions when they are not being processed. Secondary storage is more permanent than main memory, since data and instructions are not lost when the power is turned off. It is also much cheaper than primary storage and is unlimited since you can have as much of it as you can afford. The most commonly used auxiliary storage devices are magnetic storage (tapes and disks), optical storage (CD ROM, CD-R, DVD-ROM, DVD-R and DVD-RW and solid state memory (flash memory and USB drives).

Peripheral DevicesPeripheral devices are any device controlled or monitored by the CPU. It includes both input and output devices.Input DevicesInput devices are any device that is used to put data and instructions into the computer. Some commonly used input devices are keyboard, mouse, joystick, digital camera, scanners, barcode readers and magnetic strips.

Output DevicesOutput devices are any device that is used to get information out of a computer. Some commonly used output devices are VDU or monitor, printer, plotter, speakers and multimedia projector.

Objective 1.3: Outline the functions and uses of primary storage devices.

Content: PROM, EPROM, RAM, ROM

Notes: Primary StorageThis is a group of silicon chips that resides on the computer’s motherboard (main circuit board). Primary storage consists of two types of memory chips: RAM and ROM chips. A memory chip is an integrated circuit (IC) made up of millions of transistors and capacitors.

RAMThis chip is used to hold data and instructions (programs) temporarily while processing is taking place using that data and program. It also holds the data that results from processing – data that is waiting to be output or stored in a secondary storage device. RAM is volatile i.e. it is temporary and changeable. If the power is turned off or the computer is rebooted (started up again) all the information held in RAM will be lost.

ROMThis chip holds data and instructions necessary for starting up the computer when it is switched on. It is used to store system-level programs such as the BIOS (Basic Input Output System) program.

Variations of ROMProgrammable ROM (PROM) This type of ROM can be programmed only once using special equipment. It is useful for companies that want to make their own ROMs from software they write themselves. If they change their code they can create new PROMs without requiring a ROM manufacturer.

Erasable programmable ROM (EPROM)This type of ROM can be erased and reprogrammed, which makes it more useful than a PROM. EPROM chips are programmed in the same way as PROM chips. Data is erased from this chip by exposing it to ultraviolet light of a specific frequency for a specified period of time.

Objective 1.4: Manipulate units of storage.

Content: Bistable devices, bit, byte, kilobyte, megabyte, gigabyte, terabyte, word, word size

Notes: Units of StorageMemory is made up of bistable devices. Bistable means the components that make up memory can be set to one of two states either on or off. These two states are represented using binary digits- 0 for off and 1 for on. As such, the smallest unit of storage of memory is called a binary digit (bit). The amount of data and instructions that can be stored in primary storage or secondary storage media is measured in bytes.

ByteA byte is made up of a combination of 8 bits and has the capacity to represent one character i.e. a letter, a number, a symbol, a punctuation mark or a blank space.

WordA word is the amount of bits the computer can process in one operation.

Word sizeA word size or word length is the number of bits in a word.

Larger Units of Storage

Name Symbol Number of bytes Equal to

Kilobyte KB 1024 1024 bytes

Megabyte MB 1048576 1024 KB

Gigabyte GB 1073741824 1024 MB

Terabyte TB 1099511627776 1024 GB

Petabyte PB 1125899906842624 1024 TB

Exabyte EB 1152921504606846976 1024 PB

Zettabyte ZB 1180591620717411303424 1024 EB

Yottabyte YB 1208925819614629174706176 1024 ZB

Objective 1.5: Compare the types of secondary storage media w.r.t. portability, speed and capacity.

Objective 1.6: Use terms associated with storage devices.

Content: Magnetic tape, floppy disk, hard disk (fixed head, moving head, external), optical disks (CD, DVD), flash drive, flash memory cards, sequential access, direct access, sectors, tracks, read/write head; device interfaces such as : SCSI, IDE, SATA

Notes: Secondary Storage Media

Secondary storage devices are chosen for a particular use based on their: Storage capacity (how much data the device can store) Access speed ( the time needed to locate the data and transmit it to the CPU) Portability ( ability to be easily removed and used on another system) Cost Size (necessary for storage on shelves or portability)

Magnetic tapeA magnetic tape looks like an audiocassette tape. Tapes may come in different sizes. It is used mainly to backup hard disks because it can store large amounts of data at a low cost. Accessing data on a tape is very slow since data is stored sequentially. Sequentially means that data is retrieved in the order which it was stored. As of 2008, the highest capacity tape cartridges can store 1 TB of data. A tape drive is used to read data from and write data to the tape. The tape drive may be external or built into the system unit.

Magnetic disks (Floppy disk, Hard disk)

All magnetic disks provide direct access to stored data. This means that you can go directly to specific piece of data without having to access any other either before or after the data you want.

Floppy disk

This is also called a diskette. It is a removable, flexible plastic disk, coated with a magnetisable material. The disk is held in a plastic case, usually 3.5 inches by 3.5 inches in dimension. The plastic case protects the disk from dust and grease. The floppy disk is used to store and transfer small amounts of data between computers. A 3.5 inch floppy disk holds up to 1.44 MB of data.

Data and information is written to or read from the disk by a read/write head in the disk drive held in the system unit. Data is stored on both sides of a diskette on tracks and sectors. Tracks are a set of numbered concentric rings. The tracks are also divided into wedge shaped pieces known as sectors, which are also numbered. A sector is the amount of data that can be read from or written to a disk by the computer in one read/write operation.

Before data is stored on a floppy disk, it needs to be formatted. Formatting means writing electronic information on the disk so that the computer can recognize the disk as a valid storage device where data can

Sector

Track

be stored. Most floppy disks are already formatted when they are purchased. If a diskette is formatted after data has been stored to it, the information will be deleted.

Hard disk

A hard disk is a thin but rigid, inflexible disk made of highly polished metal. The surface of each side of the disk (also called platters) is covered with a substance that can be magnetized. As of April 2009, the highest capacity HDDs is 2 TB. There are different types of disk: moveable head, fixed head and external. Moveable head hard disks have one read/write head per disk. Fixed head disks have a read/write head for every track on the disk.

The access time (time to get data) from a spinning disk with one read/write head is a combination of:

Seek time – how long it takes the head to get to the right track;

Rotational delay or latency time – how long it takes for the data to rotate under the head; and

Transmission time – the time taken to read the data and transmit it to the CPU.

Consequently, the access time for a fixed disk is less than that of a moveable disk, since each track has a read/write head and this eliminates the seek time.

The external and removeable hard disks are portable hard disks that are connected to the system unit. External hard disks have very large storage capacities, up to 1.5 TB currently. They are used mainly by very large computers. Hard disks are more reliable than floppy disks since its platters are fixed and seal in a unit. Hard disks can store much more data than floppy disk and optical disks and access and transmission of data is faster.

Like floppy disks, a hard disk must also be formatted before any data can be stored on it. Formatting sets up the tracks, sectors and cylinders. A cylinder is made up of all the tracks of the same number from all the disks that make up the hard disk.

Optical Disks

Optical disks are disks that are read by laser lights. They are made from plastic. The data is stored on layers inside the plastic. CDs and DVDs are the two main types of optical disks.

Compact Disc

A Compact Disc (CD) is an optical disc used to store digital data. The physical dimension of a CD is 12 cm or occasionally 8 cm in diameter. CDs can hold up to 750 MB. They are three types of CDs: CD-ROM, CD-R and CD-RW.

CD-ROM (read only)

This type of CD is used for: Storing multimedia (text, graphics, sound and videos). Storing software packages for sale or distribution e.g. application software packages such as

encyclopedias, word processors, training programs, games and graphics packages.

CD-R (recordable)

This type of CD is used for: Storing large volumes of data that does not need to change e.g music CDs.

CD-RW (re-writeable)

This type of CD is used for: Storing large volumes of data that change frequently e.g backups copies

DVD

"Digital Versatile Disc" commonly called “DVD” is an optical disc storage media that can be used for storing movies with high video and sound quality. DVDs look like compact discs, their physical dimensions are the same (12 cm or occasionally 8 cm in diameter). DVDs are encoded in a different format to CDs and they have a much higher density (more data is stored per unit area). Some DVDs are double sided i.e. they can hold data on both sides. DVDs can hold between 4.7 GB and 17 GB of data. Three types of DVDs are the DVD-ROM (read only), DVD-R (recordable) and DVD-RW (rewritable).

USB Flash drive

USB Flash drives are storage devices which consist of a small circuit board encased in a plastic or metal casing

built with a USB interface. They are typically small, lightweight, removable and rewritable. As of November

2006 to present, memory capacities for USB Flash drives range from 32 MB up to 64 GB. Flash drives are more

compact, generally faster, hold more data and may be more reliable (due to their lack of moving parts) than

floppy disks.

Common uses

USB interface

1. Personal data transport

The most common use of flash drives is by individuals to transport and store personal files such as

documents, pictures and video.

2. Computer repair

Flash drives are used to transfer recovery and antivirus software to infected PCs.

3. System administration

Flash drives are used by system and network administrators, who load them with configuration

information and software used for system maintenance, troubleshooting, and recovery.

4. Application carriers

Flash drives are used to carry applications that run on the server computer without requiring

installation.

Flash Memory Cards

These come in the form of a card shaped like a stick of chewing gum, with dimensions 21.5 x 50 x 2.8 mm and storage capacities up to 64 GB. They are a special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. They are used in PDAs (personal digital assistants), laptop computers, digital audio players, digital cameras, mobile phones and video game consoles.

Storage Device – Capacity, Advantages and Disadvantages

Storage Device Storage capacity

Advantages Disadvantages

Magnetic tape Up to 1 TB Easy to transport and store Cheap Mostly used for backup or

archives

Provides sequential access to data stored

Limited shelf-life (2 years) Must be stored in a suitable

environment (smoke, dust, temperature and humidity must be carefully controlled)

Difficult to update files (cannot make changes to a record without writing over the entire tape)

Floppy disk 1.44 MB Provides direct access to data stored

Small and very portable Easy to store Suitable for backing up

Small storage capacity (unsuitable for storing files containing graphics)

Limited shelf-life (2 years) Slow to read/write speeds

small files Data security (e.g. you can

store small files that you don’t want other computer users to see)

Fixed hard disks Up to 2 TB Direct access Fast data transfer speeds Vast storage capacity

Not portable

Removable hard disks

Up to 1.5 TB Direct access Fast data transfer speeds Vast storage capacity

compared to diskettes portable

computer must have a USB port

Optical disks CD: up to 8MBDVD : up to 17 GB

Direct access Fast data transfer speeds Vast storage capacity

compared to diskettes Portable Can be cleaned easily with

a soft cloth Unaffected by magnetic

fields

Data on CD-ROMs cannot be changed

Access times are slower than hard drives

Flash memory Up to 64 GB Physically very small Highly portable High data transfer speed to

PCs Large storage capacity

compared to diskettes Direct access

May need special software to be used with PCs

Limited storage compared to CD or DVD

USB drive Up to 256 GB Easy to use Convenient (small size –

can be placed in a pocket or on a key chain)

Large storage capacity compared to diskettes

Highly compatible - ‘plug and play’ (no software needed)

Fast access, direct access Password protection Disk write protection

switch (prevents data from being accidentally written over)

May not be easily read with computers using Windows 98 or older operating systems

Notes: Device Interfaces

These are connectors and cables used to transfer data from the CPU to input, output and storage devices. There are different standards or technologies used to design these devices. Three main standards used are:

1. SCSI2. IDE3. SATA

Small Computer System Interface (SCSI)

It is a set of standards for physically connecting and transferring data between computers and peripheral devices. SCSI is most commonly used for hard disks and tape drives, but can connect a wide range of other devices, including scanners and CD drives.

SCSI Ribbon cables Two SCSI Connectors

Intelligent Drive Electronics or Integrated Drive Electronics (IDE)

This interface is used specifically for mass storage devices, in which the controller is integrated into the disk or CD-ROM drive.

A device controller is a part of a computer system that interprets the signals going to, and coming from the CPU processor. There are many device controllers in a computer system. Any device connected to the computer is connected by a plug and socket, and the socket is connected to a device controller. Device controllers play an important role in order to operate that device. It’s just like a bridge between the device and operating system.

IDE port connector IDE motherboard connectors

Serial Advanced Technology Attachment (SATA)

This is a computer bus primarily designed for the transfer of data between a computer and mass storage devices such as hard disks drives and optical drives.

A computer bus (often simply called Bus) is a part of some computers used to transfer data, signals or power between some of the components that make up a computer. Computer buses are used to:

Link between the CPU and on-board Memory. Link between multiple CPUs in a multi-CPU system Link the Arithmetic logic unit to the rest of the CPU Connect hard drives, graphics cards, etc to the main system. Connect SATA, USB and Firewire.

SATA power cable SATA ports on a motherboard

Objective 1.7: Explain the uses of various input devices and media

Content: Optical mark reader(OMR), character readers(OCR, MICR), mouse, joystick, barcode reader, document scanner, light pen, touch terminals, Voice Data Entry/voice recognition, graphics tablets, point of sale(POS), keyboard, digital camera, biometric systems, sensors, remote control, sound capture, pointing devices, webcam

Notes: Input Devices

Optical Mark Reader (OMR)

OMR detects the position of marks on paper. The marks must be made in pre-defined positions. The OMR detects the intensity of the light reflected from these marks. The computer records the position of the marks and analyses it determine the meaning of the data e.g. right or wrong answer on a multiple choice quiz. OMRs are used for correcting multiple choice examinations, analyzing data from surveys, counting election ballots and validating lottery tickets.

Magnetic Ink Character Recognition (MICR)

MICR is mainly used by the banking industry to read cheques. Cheques have the following information encoded in them:

The cheque number The bank branch number The customer’s account number The amount of money written on the cheque

The amount is written using special magnetic ink which contains iron oxide. The characters on the cheque are written in a special font and are recognized electronically as it passes through the device. The MICR can only recognize a specific font and a limited number of characters.

Advantages of the MICR:

Documents are difficult to forge Documents can still be read after being folded, soiled etc.

Disadvantages of the MICR:

MICR readers are expensive The system can accept only a few characters

Optical Character Recognition (OCR)

This is an optical scanner which utilizes special software to read characters from paper. The shapes of different characters are detected by shining light on them from a photo-electric device and sensing the patterns of reflected light. The reader software allows each character pattern to be compared with a set of stored patterns until the closest match is found. The match is then translated into text in the computer so that it can be manipulated by the user. It is used in the legal service, postal service, utility and financial companies and by immigration officers at airports.

Advantages of the OCR

OCR is suitable for converting large volumes of printed data into electronic text on the computer so that it can be manipulated. It is great for archiving books, documents etc

Disadvantages of the OCR

OCR has difficulty understanding handwritten text if the letters are not properly formed. OCR has difficulty recognizing unusual fonts.

Mouse

The mouse has a ball underneath, which rolls and determines the direction of the cursor, and buttons which allow the user to make selections. Some mice (plural of mouse) have a scroll wheel that allows you to scroll through long documents. In addition to moving the cursor, the mouse is used to select and open documents or programs, move icons from one place to another on the screen, select options from a menu, position the cursor when preparing and editing documents, and for drawing lines and sizing graphic objects such as pictures.

Joystick

This device is used to control movement of the cursor or other objects on the screen by operating a small lever. It is used mainly for playing games, but it is also used with scanners at hospitals.

Barcode Readers

Barcodes are read by a scanner in which a laser beam scans the barcode and the light is reflected back into the scanner. The information received by the scanner is sent for processing. Barcode readers give fast error-free data entry into the computer. It is a fast method of recording the sales of items. Barcode readers are used in supermarkets, libraries, research, airports, postal services and warehouses.

Document Scanners

These scan text and pictures into the computer. There are many types of scanners:

1. Flatbed scanner: the picture is placed on a flat surface and the image is captured, similarly to how a photocopying machine works.

2. Handheld scanner: the picture is read while the user drags the scanner over it. The quality of the image provided by this scanner is poor, but it is useful for quick data capture.

3. Drum scanner: the document to be scanned is mounted on a glass cylinder. These are used in publishing industry (magazines, books) to capture images with high detail.

4. Sheet-fed scanner: the sheet that contains the image is fed through rollers and the picture is scanned as the paper passes through.

Light pen

This is shaped like a pen and is connected to a VDU/monitor. It allows you to point and make selections more accurately on a screen. The tip of the light pen contains a light-sensitive element which, when placed against the screen, detects the light from the screen and enables the computer to identify the location of the pen on the screen. Making selections with a light is far more accurate than using your finger to make selections on a touch sensitive screen. They also allow you to draw directly on the screen. However they are not as accurate as a digitizing tablet and drawing can become uncomfortable.

Touch Terminal

A touch terminal, also known as a touch screen is a light-sensitive screen that detect when a person touches it, as well as the area of the screen that was touched. Various options are displayed on the screen and the user presses the one they want. Touch screens are used on ATMs, microwave ovens, cash registers, at airports, fast-food outlets, theatre booking offices, etc.

Advantages of the Touch Terminal

The user can select the option very quickly.

The user does not require any training to use it.

Disadvantages of the Touch Terminal

The system is expensive.

It is limited to certain applications.

Voice Data Entry/voice recognition

This type of system requires the use of a microphone. It accepts the spoken word as input data or commands. The computer is programmed to recognize certain patterns of speech. The microphone is used to code human speech into a sequence of electronic signals. These signals are compared to a set of stored patterns. If they match, the command or data being entered is accepted by the computer and processed. Voice commands can be used to control machines or even enter documents in a word processor. It is very useful for physically disabled persons.

Advantages of the Voice Data Entry

No typing is required

The system can be used remotely e.g. by telephone

Disadvantages of the Voice Data Entry

Recognition of words is still relatively slow since human speech can vary in tone and emphasis of various parts of words and phrases.

The system is not suitable for use in noisy places.

You may need to program (train) the system to understand your particular voice patterns.

Digitizing tablet

This device looks like a small chalkboard. The tablet detects and transfers drawings made on it to the screen. The drawings are made with either a stylus (pen-like pointing device) or a puck (mouse-like device). Graphics tablets are used by architects, mapmakers, artists and designers to create sketches and drawings on the computer.

Point of Sale (POS)

This is the combination of a barcode reader and computerized cash register. It is usually found in retail outlets. The barcode reader scans in information from the sale transaction and this is recorded in a centralized computer which is connected to the cash register. The information collected can also be used for stock control and sales analysis.

Advantages of the POS

Customers get quicker and more accurate service, which improves efficiency.

Supermarkets can get instant or continuous stock checks

Saves on paper

Disadvantages of the POS

Barcodes cannot be read by humans

Keyboard

This device is used to enter text data or characters e.g. letters, symbols, numbers and commands specific to a program.

Digital cameras

This camera captures an image and stores it in memory within the camera. The camera has a sensor that converts the light into electrical charges. The processor in the camera converts this information into digital data and stores it on a flash RAM card. The digital images can then be uploaded from the camera to a computer where they can be displayed, manipulated or printed. The memory can be erased so that more images can be captured. Unlike normal RAM memory the RAM card is non-volatile. The resolution of the camera is measured in pixels. The more pixels a camera has the greater the detail captured.

Advantages of a Digital Camera

Photos can be shown on a small screen on the camera, and resized and erased so that you can choose to store only the images that you want.

Disadvantages of a digital Camera

It is relatively easy to lose or erase the camera’s memory card e.g. accidentally passing it through an airport x-ray machine.

Biometric Systems

Biometric refers to the science of identifying an individual through their body characteristics such as face geometry and hand geometry e.g. fingerprints, iris or retinal scans, vein and voice patterns. All these forms of

identifying an individual can be input into a computer system set up for security purposes allowing access to buildings and bank accounts etc.

Sensors

Chemical or physical changes in humans and their environment can be converted to electrical signals using sensors that pass data to a computer, where it is analysed, stored and manipulated by specialized software. These sensors are useful in medicine, environmental planning and preservation, weather reporting etc. Sensors can be used to measure things such as heat, light, sound, pressure, strain, acidity(pH), oxygen concentration, humidity, pulse, water level, water flow, speed, tilt or even a door or valve opening or closing.

Remote Control

A remote control emits a beam of infra-red light that carries data signals. They are used to input data to televisions, stereo systems, VCRs, DVD players and by computers as a wireless means of communication.

Sound Capture

Microphones are used for sound capture. All modern computers contain built-in microphones and sound cards to allow voice or music to be recorded. The sound card digitizes the data into a form that the computer can understand.

Pointing devices

These devices are used by graphical operating systems such as Windows to show the movement of the pointer or the cursor, and enable the control and selection of objects on the display screen. This group of devices includes the mouse, trackball, pointing stick, touchpad, joystick, light pen, digitizing tablet and touch screen.

Webcam

A webcam is a video capture device connected to a computer or computer network, often using a USB port or, if connected to a network, Ethernet or Wi-Fi. Their most popular use is for video telephony, permitting a computer to act as a videophone or video conferencing station. This camera is used to record and edit video images (i.e. moving or still images). The images are stored in a format that can be displayed on a web page. Web cams are used in video conferencing. It is also useful in security surveillance.

Objective 1.8: State the types and functions of output devices.

Content: Visual display unit (VDU): resolution, types, sizes; printers: impact and non-impact, types(character, line, page, laser, inkjet, dot matrix); Characteristics: speed, quality, storage capacity; plotters; audio output devices(speakers, headphones, earphones); microfilm, hardcopy, softcopy, human readable, machine readable

Notes: Output devices

Output devices are equipment used to get information or any other response out of the computer. If the output can be read by human beings it is said to be human readable. If the output cannot be understood by humans it is said to be machine readable. Examples of output devices are display screens, speakers, printers, video graphics card, audio card (sound card) and plotters.

There are two types of output:

1. Softcopy output2. Hardcopy output

Softcopy output is temporary output e.g. information displayed on a screen or in voice or audio form through speakers. This kind of output disappears when the computer is switched off since the screen or the speakers need the computer to work.

Hardcopy output is permanent output e.g. information printed onto paper or film. It is tangible – you can hold it in your hands.

Softcopy output devices

Display Screens

Display screens (simply screens) are also called monitors or Visual Display Units (VDU). These are used to output still or moving pictures. There are two types of display screens:

1. Cathode Ray Tubes (CRT): these screens looks like a standard television set.2. Flat Panel displays: these screens are used mainly with portable computers like laptops, in some

desktop computers and even in the latest television sets. There are two (2) types of flat panel display screens:

a. Liquid Crystal Display (LCD)b. Plasma Display

Screens can come in different sizes e.g. 14 inch or 17 inch. They can be either colour or monochrome. Monochrome means black and white.

Images and text are formed by many tiny dots of coloured light called pixels. A pixel is short for picture element. A pixel is the smallest unit on the display screen.

The number of pixels determines the resolution of the screen.

Resolution is the clearness or sharpness of an image on a screen. The more pixels there are on screen, the greater the resolution. Some common resolutions are:

VGA (Video Graphics Array) = 640 x 480 pixels

SVGA (Super Video Graphics Array) = 800 x 600 pixels XGA/XVGA (Extended Graphics Array/ Extended Video Graphics Array) = 1024 x 768 pixels SXGA (Super Extended Graphics Array) = 1280 x 1024 pixels UXGA (Ultra Extended Graphics Array) = 1600 x 1200 pixels

A video graphics card is also called a video display adapter. It determines the resolution, number of colours, and speed with which images appear on the screen.

Audio Output Devices

Speakers, headphones and earphones are used to output sound. The quality of the sound depends on the type of system used, the size of the speakers and the computer’s audio card. An audio card is used to process sound in the computer.

Hardcopy output devices

Printers

One way of classifying printers is as:

Character printers: these print one character at a time similar to a typewriter. They are slow. Line printers: They print a line at a time. Multiple hammer-like keys forming a line of text hit the page

at one time. They are much faster than character printers and are used to print large volumes. They print a limited number of characters and do not print graphics.

Page printers: these print a whole page at a time. They are therefore even faster and deal with very large volumes of printed output.

Another way of classifying printers is as:

1. Impact printers2. Non-impact printers

Impact printers use a printing mechanism called a print head. They make their output by pressing the print head against a ribbon, which then hits the paper. The main types of impact printers are dot matrix, daisy wheel and drum, chain or band printers.

Dot matrix printers (character printers)

Characteristics:

Characters are formed from a matrix of dots. The speed is usually 30 – 550 characters per second (cps) It is very noisy It is relatively fast The print obtained is usually poor.

They are useful for low-quality carbon copy prints or printing on continuous sheets of paper e.g. invoices (bills).

They are not good for printing shaded graphics or photographs.

Daisy wheel printers (character printers)

Characteristics:

It is very noisy Printing is slow (less than 90 cps). The text is generally crisp and clean. The size and font produced can only be changed by using a different daisy, as the characters on the

wheel are fixed.

N.B. This printer is obsolete

Drum, chain or band printer (line printers)

Characteristics:

They are fast (2500 lines per minute. They are used to print large volumes of information.

Non-impact printers are faster, quieter and produce better quality print than impact printers. Unlike the impact printer, the printing mechanism makes no contact with the paper. The main types of non-impact printers are laser printers, inkjet printers and thermal printers.

Thermal printers (character printers)

There are two types of thermal printers:

Direct Thermal printer: this printer uses heated pins to form the characters. These pins come into contact with special heat-sensitive paper to form darkened dots when the pins reached a specific temperature, thus shaping the characters. The pins actually burn the dots into the specially coated paper. Exposure to sunlight and heat tends to darken the thermal paper. The print quality is poor.

Thermal wax transfer printer: the print head of this printer melts a wax-based ink from a transfer ribbon onto paper. This printer does not require special paper.

Thermal printers are used in portable calculators, fax machines and some ATMs (automated teller machines).

Inkjet printers (line printers)

Inkjet printers produce their output by spraying small droplets of ink at high speed into paper, in a pattern. These printers can print in both black-and-white and colour. They used at home and small offices. The print

quality is good but not as good as the laser printer. Inkjet printers can also produce both text and graphics. They are cheaper than laser printers.

Laser printers (page printers)

These use a process similar to that of a photocopying machine. They are used in large companies or institutions such as schools. They can also be found in modern offices. A laser beam and dry powdered ink called toner produces a very fine dot matrix pattern. This pattern is transferred to the page and then fused onto it by heat and pressure. These printers can print in black and white or colour. These printers can produce more than 40 pages per minute (ppm). The print quality is very good. Laser printers produce both text and graphics. They are very expensive.

Plotters

Plotters use different printing processes e.g. some work like an inkjet printer and others use the same method as laser printers. They are used to produce documents with high quality graphics in a variety of colours e.g. maps, architectural drawings and charts. They can print on large sheets of paper. There are three main types of plotters:

Pen plotters: these use a mechanical arm or rail that holds a pen which can be moved across the page. Inkjet plotters: these work in the same way as inkjet printers by spraying ink onto the paper. Electrostatic plotters: these work in the same way as laser printers.

COM (Computer Output on Microfilm/Microfiche)

COM is a method that is used to store computer documents by reducing them in size to fit on very small photographic sheets of film. They are used to store large volumes of data. These sheets can be read using a special magnifying machine. Microfilm is a roll of film and microfiche is a rectangular sheet of film on which many frames/pages of information can be stored.

Objective 1.9: Describe how data are stored and manipulated within the computer.

Content: Binary, octal and hexadecimal number systems; binary addition and subtraction. Integers (positive and negative); sign and magnitude, BCD, two’s complement; representation of characters, ASCII.

Notes: Data Representation and Storage

The binary system is used by computers to represent data. This number system uses two digits, 0 and 1. These two binary digits are known as bits (short for binary digits). Different ways are used to store data based on its medium and type.

Representing Numbers

The number of bits used to represent a number determines the range/number of values that can be represented. For example, a single bit can represent one of two values, 0 or 1. Therefore the number of values a bit can store is two, 0 and 1. Likewise, a group of two bits can be used to represent one of four values, 00, 01, 10 or 11. Therefore the number of values two bits can store is four. To determine how many values any number of bits can store, the following formula is used 2n, where n represents the number of bits being used. Therefore, a group of three bits can represent 23 values, i.e. 8 values, which are 000, 001, 010, 011, 100, 101, 110 or 111.Converting decimal to binary

This involves dividing the decimal (base 10) number by 2 and recording the remainders until the result is zero, then writing out the remainders from left to right but starting from the bottom up.

1510 = 11112

Representing a number using a bit pattern of a given size

A number can be represented using bit patterns of different sizes. For example, the 4-bit representation of 15 is 1111 and the 8-bit representation of 15 is 00001111. Zeroes are added to the left of the binary conversion of the number to make up the number of bits required. The zeroes do not change the value of the number. (N.B. The number must be within the range of values that can be represented, using that number of bits.)

Converting a binary number to decimal (base 10)Find the sum of the values of each digit in the binary number. For example, 101102 to decimal

24 23 22 21 20

2 1510

2 7 R 1

2 3 R 1

2 1 R 1

0 R 1

16 8 4 2 1

1 0 1 1 0

The value of each digit is the digit multiplied by its place value i.e. 1x16=16, 0x8=0, 1x4=4, 1x2=2, 0x1=0 The sum of the values is 16 + 0 + 4 + 2 + 0 = 2210

Therefore 101102 is 2210.

Adding binary numbersTo add two binary numbers use the following points:

(a) 02 (b) 02 (c)

12

+ 02 + 12 + 02

02 12 12

(d) 12 (e) 12

+ 12 + 12

102 + 12

112

For example, 10112 + 00112

1 1

1 0 1 12

+ 0 0 1 12

Place value

Binary digits

1 1 1 02

Representing Signed Integers

Signed integers are positive or negative whole numbers. In binary there are many ways of representing signed number. Four common methods are:

1. Sign and magnitude

2. Ones complement

3. Two’s complement

4. Binary Coded Decimal (BCD)

Sign and Magnitude

In this method the leftmost bit is used to represent the sign (positive or negative) and the remaining bits represent the magnitude. A 0 bit indicates that the number is positive (+) and a 1 bit indicates that the number is negative (-). N.B. The integer zero is neither negative nor positive, but is represented using all zeroes.

Example, if asked:

Give the 8-bit representation of -3510 using sign and magnitude.

Solution: 1. Find the binary of 3510 => 1000112

2. Add two zeroes to the left to get 8 bits => 001000112

3. Change the leftmost bit to a 1 since you need to represent -3510

One’s Complement

Positive numbers are represented as unsigned binary. The negative numbers are represented by flipping all the digits in the binary equivalent of the number. This means replacing all the zero bits with one bits and replacing all the one bits with zero bits. N.B. The number should be expressed in the bit pattern size required before the bits are interchanged.

Example, if asked:

Give the 8-bit representation of 1310 using one’s complement.

Solution: 1. Find the binary of 1310 => 11012

2. Add four zeroes to the left to get 8 bits => 000011012

3. Interchange 1 bits for 0 bits and vice versa => 111100102

Two’s Complement

This is the most common method used to represent signed numbers. Positive numbers are represented as unsigned binary. To represent a negative number using this method, begin by finding the one’s complement of the number, then add 12 to the result.

Example, if asked:

Give the 8-bit representation of -710 using two’s complement.

Solution: 1. Find the binary of 710 => 01112

2. Add four zeroes to the left to get 8 bits => 000001112

3. Interchange 1 bits for 0 bits and vice versa => 111110002

4. Add 12 to the result => 111110002 + 12 = 111110012

Sometimes in using two’s complement, results end up with one bit too many. This is dealt with by discarding the leftmost bit.

Subtracting in Binary Using Two’s Complement

To subtract numbers in binary, find the negative of representation of the number being subtracted, using two’s complement. Then add it to the number that it is being subtracted from.

Example, if asked:

Subtract 01102 from 10012

Solution: 1. Express 10012 - 01102 as 10012 + (-01102)

2. Find the two’s complement representation of -01102 => 10012 + 12 = 10102

3. Add 10012 to 10102 => 100112

Binary Coded Decimal (BCD)

In this method each digit of a number is represented as its four- bit binary code. The sign of a number is represented using a 4-bit code also. The 4-bit representation of positive(+) is 1010 and negative(-) is 1011. The sign code is placed to the left of all other bits.

Example, if asked:

What is the BCD representation of -25610?

Solution: 1. Find the 4-bit representation of each digit => 2 = 0010, 5 = 0101 and 6 = 0110

2. Put each 4-bit representation together => 0010010101102

3. Attach the sign code to the left of the result above => 10110010010101102

Representing Numbers Using the Octal and Hexadecimal Number System

The Octal and Hexadecimal Number Systems were developed to deal with concerns programmers had when representing data in binary. There was often the tendency to make transposition errors and calculation errors because of the many zeroes and ones. In addition, representing data in binary requires a lot of storage.

Octal (Base 8)

This system uses the digits 0, 1, 2, 3, 4, 5, 6, 7.

Converting From Binary to Octal

This can be done by:

1. Separating the binary number into groups of three (3) bits starting from the right; then

2. Convert each group of bits to find its decimal equivalent.

Example, if asked:

1. Convert 0011011012 to octal.

Solution: 1. Separate the binary number into groups of 3 bits, from the right => 001 101 101

2. Convert each group to decimal => 1 5 5

Therefore, 0011011012 = 1558

2. Convert 22410 to octal

Solution: 1. Convert 22410 to binary => 111000002

2. Separate into groups of 3 bits => 11 100 000

3. Convert each group to decimal => 3 4 0

Therefore, 22410 = 3408

Converting From Octal To Decimal

The method is the same as converting from binary to decimal. The only difference is the place values are found using powers of 8.

For example, 2138 to decimal

82 81 80

64 8 1

2 1 3

The value of each digit is the digit multiplied by its place value i.e. 2x64=128, 1x8=8, 3x1=3 The sum of the values is 128 + 8 + 3 = 13910

Therefore 2138 is 13910.

Hexadecimal

This is a base 16 numbering system; it uses 16 symbols (the digits 0-9 and the letters A to F).

Hexadecimal Table

Decimal Numbers

Hexadecimal Numbers

0 0

1 1

2 2

3 3

4 4

5 5

6 6

7 7

8 8

9 9

10 A

11 B

12 C

13 D

14 E

15 F

Converting From Binary to Hexadecimal

This can be done by:

3. Separating the binary number into nibbles (4 bits) starting from the right; then

4. Convert each nibble to its decimal equivalent.

Example 1 Convert 2410 to hexadecimal (use 8 bits).

Solution: 1. Convert 2410 into binary =>000110002

2. Separate the binary number into nibbles, from the right => 0001 1000

3. Convert each nibble to its decimal equivalent => 1816

Therefore, 2410 = 1816

Example 2 Convert 22410 hexadecimal (use 8 bits).

Solution: 1. Convert 22410 into binary =>111000002

2. Separate the binary number into nibbles, from the right => 1110 0000

3. Convert each nibble to its decimal equivalent => 1410 010

4. Since 1410 is represented as E

Then, 22410 = E016

Representing Characters

Data that is represented in computers is made up of characters. Characters include:

Numbers (0 to 9)

Alphabetic (lowercase letters and uppercase letters)

Special characters (punctuation marks : , $ / etc.)

Control characters (backspace, delete, insert etc.)

All the characters that a computer can store and process are called the character set of the computer. Different types of computers may have slightly different character sets, depending on their operating system. Each character is represented by a code consisting of eight bits, called the character code. The most common code used is the American standard Code for Information Interchange (ASCII). This code uses seven bits to represent each character plus an extra bit called the parity bit which is added to help ensure data integrity.

The standard ASCII code defines 128 character codes (0 to 127) where the first 32 are control codes. A control code is a non-printable code that is used to tell the computer to carry out a command. Programmers use these codes to assign commands they may want to personalize in computer.

ASCII Table

Objective 1.10: Interpret the hardware specifications of a computer system.

Content: CPU type and speed; memory: capacity, type, word size, speed. Hard drive: capacity, speed; firewire, expansion slots, ports.

Notes: Computer Specifications

Use the following to guide you when required to interpret computer specifications:

CPU:

Types:

o Make / Brand: Intel or AMD o Models: Pentium, Athlon, Celeron, Duron etc.

Speed: Gigahertz (GHz) ranging from 4 GHz up word size: How many bits it can input/output and process at a time, 32-bit or 64-bit

Hard Disk Drive (HDD):

interface connector/controller: PATA Parallel ATA or SATA Serial ATA Capacity: Gigabytes(GB) ranging from 80GB to 500GB Speed: Revolutions /rotations per minute (rpm) usually 7200 rpm for desktops and 5400 rpm

for laptops

Memory:

Types of Random Access Memory (RAM):o DDR: Double Data Rate o DIMMs: Dual In-line Memory Modules o DDR3: Double Data Rate type 3 o DDR2: Double Data Rate type 2 o SDRAM: Synchronous Dynamic Random Access Memory

Capacity: Gigabytes(GB) ranging from 2 GB up Speed: Megahertz (MHz) ranging from 533 MHz and up

Expansion slots: Slots on motherboard used to attach additional devices. Examples are

PCI slots (Peripheral Component Interconnect) for attaching general hardware AGP slot (Accelerated Graphics Port or Advanced Graphics Port) for attaching video cards

Ports: An interface on a computer to which you can connect a device. There are several types. Some types are specific to certain devices. Some of them are:

Serial Parallel USB (Universal Serial Bus) FireWire Audio

PCMCIA (Personal Computer Memory Card International Association).

PCI PS/2 Ethernet

Objective 1.11: Distinguish between system programs and application programs.

Content: systems software: operating systems, translators, utilities; Application software: general purpose, special purpose, custom written, customized, integrated software

Notes: Software

Software is the name given to all programs that computers use to perform different tasks.

Types of software

There are two main categories of software:

1) Application software 2) System software

Application software:

Application software can also be referred to as Application packages. These programs are

developed to perform specific tasks or solve a particular problem. Application software includes

entertainment software such as games, home or personal software such as CD-ROM

encyclopedias, productivity software such as word processing, spreadsheet packages and

graphics. Application packages can also be grouped as follows:

1) General purpose software

2) Integrated software

3) Specialized software

4) Customized software

5) Custom written or tailor-made software

General purpose software:

This is software that is not written for any specific business. It can be used to suit specific needs

e.g. a teacher can use a spreadsheet package to prepare students` end of term grades reports

and the same spreadsheet software can be used by a salary clerk to prepare pay sheets and

bills. General purpose software is also called “off the shelf” software. They are well tested and

are usually relatively cheap.

Three commonly used general purpose packages are:

1) Word processing packages

2) Spreadsheet packages

3) Database packages

Word processing packages:

These packages are also called word processors. They allow you to prepare documents such as

letters, reports, memos, books or any type of correspondence on a computer. Some popular

word processors available are Microsoft Word, Lotus Word Pro and Word Perfect.

Spreadsheet packages:

These packages allow you to organize information into rows and columns so that it can be

operated on easily. It enables you to store numerical data. Some common spreadsheet

packages in use today are Microsoft Excel, Lotus 123 and Quarto Pro.

Database software:

These programs allow you to organize and store related data together, so that specific pieces of

information can be retrieved easily and quickly. Some common database packages in use today

are Microsoft Access, Oracle and MySQL.

Integrated Software:

An integrated software package offers many single purpose programs together as one. These

packages allow data to be transferred easily between the programs. A basic integrated package

may contain a word processor, spreadsheet, database, communication and graphics

presentation program. Examples of integrated software are Microsoft office, Microsoft works,

Lotus SmartSuite and ClarisWorks.

Specialized software:

This is software that is written for a specific task. These programs provide features for the

purpose for which they were designed e.g. AutoCAD which was designed specifically to draw

engineering and architectural designs.

Customized software

This is general purpose software which has been modified to meet the needs of its users

(company or individual) better. This is done by writing short programs called macros and adding

them to the general purpose software.

Custom written software:

This is software that has been created to meet the unique requirements of a particular

individual or company. It may be created by individuals within the company or given to a

software house to be created. A software house is a company that specializes in writing

software.

System software

These are programs that manage and support the resources and operation of the computer

system. They enable the running of application software and the management of the system

resources. System software includes operating systems, utility programs and language

translators.

Operating system (OS):

An operating system is a set of programs that controls the operation of a computer. The

computer cannot work without the operating system software. As soon as the computer is

switched on the operating software on the computer is activated and loaded into main

memory. The process of loading the operating system software into memory is called booting.

Some operating systems used in computers are Windows 7, Windows Vista, Windows XP, Linux,

UNIX and the Macintosh Operating System (e.g. MAC 0SX).

Language Translators

A translator is a program that translates one programming language instruction(s) into another

programming language instruction(s) without the loss of original meaning. Examples of

translators are interpreters and compilers.

Utility Programs

These allow a user to perform maintenance-type tasks usually related to managing the

computer, its devices, or its programs. Most operating systems include several utility programs

for managing disk drives, printer and other devices and media. Examples of utility programs

are:

Disk defragmenters can detect computer files whose contents are broken across several

locations on the hard disk, and move the fragments to one location to increase efficiency.

Disk checkers can scan the contents of a hard disk to find files or areas that are corrupted in

some way, or were not correctly saved, and eliminate them for a more efficiently operating

hard drive.

Anti-virus utilities scan for computer viruses.

Objective 1.12: Explain the functions of the Operating Systems.

Objective 1.13: Distinguish among multitasking, multiprocessing and multiprogramming.

Content: File management, memory management, security, device management,

input/output management, user interface, process management

Notes: Functions of the Operating Systems

The operating system has several functions:

1. Managing computer resources: it allows software and hardware to communicate with

each other and manages the use of input and output devices.

2. Managing files and memory: It keeps track of the locations where programs and data

are stored within the computer’s memory and on secondary storage devices. It is also

responsible for the copying, deleting, renaming and backing-up of files.

3. Maintaining security: It prevents unauthorized users from accessing a computer. A

register of all the users’ names and passwords are kept so that anyone who tries to

access the computer must have their username and password verified before they are

allowed to access the computer. It also keeps a record of who accessed the computer,

the length of time it was used by that user and what they did.

4. Managing tasks (processes): It allows the computer to facilitate multitasking,

multiprogramming and multiprocessing. Multitasking allows the computer to appear to

perform many tasks simultaneously (at the same time) e.g. you can play music and type

your IT project at the same time. Multiprogramming allows the computer to appear to

run more than one program at the same time, although at a specific time the CPU is

dealing with only one instruction for one of the several programs being run.

Multiprocessing allows more than one program to run at the same time by linking two

or more computers or processors which can then work on different programs or

different parts of the same program at the same time.

Objective 1.14: Explain the different types of processing modes.

Content: Batch processing, real-time, on-line, time-sharing.

Notes: Processing modes

The OS also facilitates different processing mode that are selected based on its suitability for

the job to be performed. There are four modes of processing:

(1) Time –sharing: this mode is used in multi-access systems where a single CPU is

shared by several users using individual terminals. This method of processing makes

the user believe they have continuous access to the CPU when in fact each user is

given a time slice (small amount of processing time) in turn. This mode of processing

is used at universities where students and lecturers are allowed access to a central

CPU on a mainframe via different terminals throughout the campus.

(2) Batch processing: in this mode the programs and data are collected together in a

batch queue before processing starts. The program and data collected is called a job.

Usually jobs are stored during working time and executed when the computer is

least in use (during the night). This is done in this manner since it does not require

human interaction during processing, once the batch starts it continues until it is

done or an error occurs. This mode is suited for payroll processing, processing utility

bills and credit card billing.

(3) Real-time processing: in this mode the system is automatically updated when a

change or transaction is made. It is interactive, allowing the user and the system to

be in constant communication with up-to-date information. This mode is suitable for

stock systems, airline booking systems, electronic funds transfer systems and control

systems.

(4) Online processing: a system in this mode has access to a network. Unlike the real-

time processing system, an online processing system is not updated automatically,

so information is not always current and must be updated frequently.

(5) Providing a user interface: It allows the user to communicate or interact with the

computer.

Objective 1.15: Distinguish between types of user interface.

Content: Software interface: Command driven, graphical user interface (GUI) , menu driven (pull-down, pop-up, icons). Hardware interface: touch screens, non-visual interface, sensors, Braille keyboards

Notes: User Interfaces

There are three (3) types of software user interfaces:

1. Command driven interface: This type of interface is used in a DOS operating system. To

communicate with the computer, the user has to type a command in codes or words

when prompt on the display screen. E.g. C :\> dir tells the OS to list all the files on the

hard drive.

2. Menu driven interface: to communicate the user can either use the mouse or arrow

keys to make a selection from a menu which contains commands e.g. Print, Save As,

Open. There are two (2) types of menus:

Pull-down menu – usually drops down from the menu bar when it is clicked.

Pop-up menu – pops up from nowhere when the right mouse button is clicked.

3. Graphical user interface (GUI): This interface is also called WIMP (windows, icons,

menus and pointing devices). To communicate with the user, it uses buttons, icons,

menus and keystrokes to choose commands, start programs and see lists of files and

other options. Icons are small pictures that represent programs, folders, files, tasks etc.

In a The GUI all objects that are related to each other are shown in a window. More

than one window can be opened on the desktop at the same time. The desktop is

common visual background which appears on the display screen when the computer

has finished booting.

Hardware user interfaces:

Touch screens

To communicate with the computer, the user touches the display of the device by a finger or

stylus. This interface incorporates aspects of GUI and allows the user to make selections and

send commands by touching icons on the screen. The interface is used for both input and

output, since you view information and the options available to you on the screen.

Non-visual interfaces

This type of interface utilizes audio (sound) and gestures (head, hand and device) to send

commands and make selections.

Sensors

This type of interface utilizes changes (chemical or physical) in the environment to

communicate with the computer.

Braille keyboards

This device aids the blind in communicating with the computer. The keys have raised dots

which represent different characters.