hardware notes for igcse computer studies 0420

Chapter 3 - Hardware

Chapter 3 – Hardware

Hardware means physical parts of the computer

Main hardware components of a general-purpose

computer

A computer is a programmable, electronic device. It receives input,

stores data, processes data and produces output.

Hardware components:

o An input device is used by the user to put data in the computer

o A processor manipulates the data that the input device gives it

o Internal memory (main memory or primary storage) holds data

and programs while the computer is on

o Backing storage (secondary storage) stores data and programs

while the computer is off

o An output device reports results to the user or causes something

to happen

The processor was originally called central processing unit (CPU). It

consisted of many sets of circuitry.

All this circuitry was put into a single silicon ‘chip’.

Known as microprocessor, processor.


Computers and processing power

The power of a computer’s processor determines what type of computer

it is.

Types of computers

Organisations can link terminals to mainframe computers.

A terminal has a keyboard for input and a monitor for output.

Most people today own a computer.

They have a disk for storing data and a processor to operate on the data.

Portable computers (laptops or notebooks) have a built in keyboard and

screen and are powered by a battery.

Palmtop computers were small enough to fit in the hand

Cheap, portable computer using less power.

Modern versions have wireless or mobile network access, called

notebooks.

Personal digital assistant (PDA) does not have a keyboard; instead it

uses a plastic stylus on a touchscreen on a virtual keyboard on the

screen.

A PDA that includes a mobile phone is one form of smartphone.

Microcontroller combines microprocessor with memory, backing

storage and other circuitry, all in a single integrated circuit.

A supercomputer is an extremely powerful computer that may contain

thousands of processors.

Processors work in parallel with each other to achieve high processing

power and speed.

Supercomputers are used to make large calculations in a short time.

Measuring processor power

Processor power is usually measured in Millions of Instructions Per

Second (MIPS).

Supercomputer power is measured in larger numbers of FLoating point

Operations Per Second (FLOPS).


Type of computer Processor power Example applications

Supercomputer Extremely powerful Process large sets of data in a short time. Weather forecasting, molecular modelling, aircraft simulations in flight or simulations of buildings in wind.

Mainframe Very powerful Used by large organisations to provide central data storage and processing power to many users: running payroll processes and creating customer invoices.

Personal computer (PC) or laptop

Powerful Used by individuals to store and process data: word processing, spread sheets, email, web browsing, playing music.

Netbook, palmtop or personal digital assistant (PDA)

Moderately powerful Used by individuals to store and process data while moving around: email, web browsing.


Input devices and their uses

Manual input devices are used by people to capture data. Automatic data

capture devices enable data to be entered without human involvement.

Manual input devices

Keyboards and keypads

On a standard keyboard, each key has a value. Letter. Numeral, punctuation mark or other symbols printed on it.

QWERTY is a layout that avoids re-training users.

The disadvantage is that they are slow compared with devices for automatic data capture. In public areas they are prone to vandalism.

A concept keyboard has a rectangular grid of keys. The program designer decides the value or command that each key enters.

Point of sale (POS) computers uses a concept keyboard. It allows the user to enter products quickly. Without having to remember or type codes.

Young children and people with learning disabilities may have difficulties using an ordinary keyboard.

A concept keyboard. With its limited number of input values, may be helpful to such people.

Public information touchscreen systems

A numeric keypad is a rectangular block of keys with the numerals 0 to 9. Numeric keypads are small, easy to use and independent language.

A disadvantage is that inputting other symbols is difficult.

Pointing devices

A mouse allows the user to point by moving the cursor in a graphical user interface.

The user selects items by switching buttons on the body of the mouse (clicking).

A mechanical mouse has a small ball underneath. The mouse converts the ball rotations in two dimensions into digital signals that send it to the computer.

An optical mouse has no moving parts – it senses changes in reflected light.

Advantages of using a mouse as a pointing device:


o Provides a fast method of input for commands o Feels natural to use because it involves pointing at things

Disadvantages of using a mouse are that: o Needs a flat surface to operate on o Easily vandalised

o Physical disable people find it difficult to use a mouse

Laptops have a touchpad, a smooth, touch-sensitive area.

A user can tap on the pad with a finger

Advantages of a touchpad are the same as for a mouse.

Disadvantage that a touchpad is very small relative to the laptop’s screen.

A trackball is an upside-down mechanical mouse.

Advantages of a trackball: o It’s stationary and doesn’t need a surface to move on o Can be built into an information kiosk and isn’t as likely to get damaged as a

mouse o People can use it if they don’t have the control necessary to user other

pointing devices

Disadvantages of a trackball: o Difficult to use for applications needing fine control o Rolling a ball is less like pointing

A joystick can act as a pointing device, by moving the cursor when the user rocks a lever connected to sensors.

It can also provide input for an embedded computer, such as a motorised wheelchair

Joysticks are used in: o Playing games o Controlling fly-by-wire aircraft or flight simulation program o Controlling a motorised wheelchair

The disadvantage is that it may be difficult to control fine movement than with a mouse.

A touchscreen is a screen that is sensitive to the touch of a stylus or a finger.

They range in size from smartphones, PDAs, tablet PCs and PC monitors.

Touchscreens are common in information kiosks or ticket machines because:

o Difficult to vandalise o Reasonably weatherproof and placed in an open area o Users need no previous knowledge of computers to operate them

A disadvantage is that people with disabilities can find them difficult to use.


A graphic tablet looks like a very large touchpad but operates with a stylus on a touchscreen

It uses signals on the tablet’s surface to work out the position of the stylus on the tablet’s surface an moves the cursor to the corresponding point on the screen.

A disadvantage is that it is difficult to match the position and motion of the stylus on the tablet with those of the cursor on the screen.

A light pen is a pointing device that can only be used directly on the screen of a cathode ray tube (CRT) monitor.

Advantages of a light pen are: o Instinctive to use o With suitable software the user can draw directly on the computer’s display o Takes up little space

Disadvantage that it isn’t very accurate and it requires a cable to connect

it to the computer, which makes it rather awkward.

Image capture devices

A scanner creates a digital photograph of a paper document.

It mechanically scans the illuminated surface of the document with single row of hundreds of light sensors.

We can save scanned data as an image file.

A digital camera has a grid of light sensors that pick an optical image.

Camera’s embedded computer scans the analogue signals from the grid of sensors.

Pixel or picture element is a single sample from a rectangular grid of samples in the final image.

When the user presses the shutter button, the shutter covering lens open so that light can enter the camera.

Camera processes and stores the data as an image file in non-volatile (secondary) memory.

Advantages of digital cameras over film cameras are\; o No cost of buying processing film o Display acts as a ‘what you see is what you get’ (WYSIWYG) viewfinder

o No long delay for processing – photos can be viewed immediately

o Easier and quicker to edit digital photos o Can be sent easily over a network or used in electronic documents

A digital video camera captures a sequence of digital photos, typically 30 images per second.

Advantages of live stream webcam: o Displaying on a website o Remote monitoring on security


Sound and music capture devices

A microphone converts sounds and vibrations into analogue signals. Microphones are connected to the computer’s sound card with a cable.

Analogue-to-digital converter that converts the microphones input signal into a stream of digitised sound samples.

Speech recognition converts speech into text input.

A Musical Instrument Digital Interface (MIDI) keyboard can provide input to a computer.

When a key is struck on a keyboard, it sends signals representing the

start of a note of a particular pitch and volume.

Remote Controls

Is a small, hand-held device with a relatively small labelled command buttons.

When a button is pressed, the remote control sends a code infrared (IR)

or radio signal to the equipment.


Devices and methods for automatic data capture

Automatic data capture can happen without human involvement.

OCR and OMR readers

Optical character recognition (OCR) software extracts text from the image data of a scanned document.

When it recognises a character, it adds the character to its output data sequence.

The text can be sent to a word processor or other application and saved.

Useful for people with visual impairments.

Disadvantage is that the text produced isn’t always accurate, particularly if the original paper document isn’t printed or has smudged text.

Optical mark reading (OMR) software extracts response data from the image of a specially prepared data collection form. Unlike OCR software, it is not designed to detect characters.

An advantage of this method of input is that it is extremely fast and accurate because the coded data are simple to detect.

Disadvantages are that the forms can only be read accurately if they are properly lined up and also dirty marks on the paper might be

misread.

MICR reader

Magnetic ink character recognition (MICR) uses software similar to OCR but it scans for numerals and symbols printed in magnetic ink.

Used in bank cheques.

Barcode reader

A barcode is a set of short parallel lines in contrasting colours, often in black on a white background.

The dark lines are thick, medium or thin.

They are designed to accurately be read by machines.

Used to identify items of merchandise, resources, membership cards or documents.

Depending on the font used, the barcode symbols represent numeric digits or alphanumeric characters.


Advantages of using a barcode for data entry are that it’s faster than using a keyboard and accurate than a person.

A disadvantage is that the barcode can become difficult to read if it is obscured by marks.

RFID tag reader

A radio frequency identification (RFID) tag reader reads an ID code from a small tag using short-range radio-frequency communication.

Manufacturers can label as many products as they want with these uniquely numbered, small, contactless machine-readable tags.

Can track where the tags location is.

Advantages of RFID technology are improved efficiency: o Of stock control o At the supermarket checkout

o Of product recalls

Disadvantages of RFID technology: o Tags cost more than a printed barcode

o Unauthorised persons may be able to read RFID tags within sealed packages in transit.

o Data flooding

Magnetic stripe reader

On the back of debit and credit cards, library cards and hotel keycards you may see a brown, black or coloured magnetic strip near the top.

The stripe has 3 independent tracks that can be programmed to store different types of information.

Advantages: o If a keycard is lost there is no way of identifying which room it’s coded to

open o Easy to write fresh data onto the stripe

o It isn’t serious if a guest leaves without returning the keycard, as the code eases to be valid

A disadvantage is that someone can read and copy or alter the data on

the card with a magnetic stripe writer, which is easily available.

Smart card reader

Debit and credit cards have always had a magnetic stripe on the back.

Stores the card number and expiry date in order to make the machine-readable.


Smart card technology is used for card payments. It’s called Chip and PIN.

The card reader uses cryptographic techniques to check that the card is authentic and isn’t expired.

The embedded chip makes it harder for a criminal to clone a card.

The user enters a four-digit personal number (PIN) code into a numeric keypad on the reader.

The improved security also allows smart card readers to be used with: o Card storing e-cash o Cards storing the holder’s medical records o Driver licence cards o ID cards storing biometric data

Biometric data capture devices

People’s physical characteristics or behaviour, known a biometric data, can be used for the purposes of authentication.

The software only has to distinguish key features of the captured data and decide whether the data’s pattern is a sufficiently good match with the biometric data pattern is a sufficiently good match with the biometric data pattern stored in the database record associated with that username or smart card.

A fingerprint reader captures the print of a finger placed on it. A specialised camera, using IR illumination, can capture an image of the

retina on iris in a person’s eye.

A microphone can be used to capture audio recording of a person’s voice from which a frequency time pattern can be distinguished.

A camera is used to capture an image of a person’s face.


Sensors

A sensor is a device that produces an electrical signal in response to a stimulus.

The stimulus may be physical or chemical.

Can produce a stream of input data automatically, with no actions by a person.

A microswitch is operated by mechanical contact. It has two states, open and close.

Supply input data to a control program.

A sensor’s analogue signal needs to be digitised (converted) into digital

data by an analogue-to-digital converter (ADC).

Temperature sensor

Produces a signal that depends on the temperature of its surroundings. The computer processes the digitised signal to display a measurement or

to control an appliance.

Used in many applications such as: o Electronic thermometers o Controlling heating systems in buildings

Pressure sensor

Produces a signal that depends on the pressure to which it is exposed.

Used in an automatic blood pressure monitor and has a microcontroller.

Light sensor

Produces a signal that depends on the level of light falling on it.

A robotic truck may be required to follow a white line painted on a dark

floor to mark its route.

Infrared sensor

IR sensor produces a signal that depends on the level of the invisible IR radiation falling on it.

All objects emit significant IR radiation.

IR radiation from hot spots on people’s skin, poorly insulated buildings, the Earth’s surface, ocean and cloud cover observed from satellite and

intruder beams.


Humidity sensor

Produces a signal that depends on the concentration of water vapour in the atmosphere.

A similar device for the use in soil is called a moisture sensor.

Used in applications such as: o Controlling a heating, ventilation and air conditioning system (HVAC) in

museums to prevent humidity in excessive air

o Maintaining sufficient humidity in air in a greenhouse o Measuring humidity for meteorological records and forecasting in a weather

station

Gas sensor

Produces a signal depending on the concentration of a particular gas or vapour.

A vehicle engine sensor for oxygen is a lambda sensor.

Breathalyser measure concentration of alcohol vapour.

Process control in the chemical industry.

Environmental monitoring of air pollution.

Advantages of using sensors to collect data are:

Collect data far more frequently than a person More reliable than a person, who may forget to take readings

Collect data from places where it isn’t possible for a person to go, such

as a chemical or nuclear reaction vessel

Disadvantages of using sensors are that they may need a power source to work

and may need regular calibration to check their accuracy.


Output devices and their uses

Monitors

A monitor is an output device that displays information from a computer on a screen.

Advantages of a monitor are that the output is immediate and visual.

Disadvantage is that it doesn’t last; when the display changes, the previous output is lost.

Cathode ray Tube (CRT) advantages: o Cheap o Image can be viewed from a variety of angles o Display a wide range of colour and brightness

Disadvantages: o Bulky and difficult to fit on a desk o Heavy and difficult to mount on a wall o A lot of reflection of ambient light from the glass screen

LCD monitor advantages: o Small and easy to fit on a desk o Light and easy to mount on a wall o Compact o Little reflection of ambient light from screen o Stability of the display and absence of flicker make it more

comfortable for viewing.

Disadvantages: o Image can only be viewed from a relatively limited range of angles o Limited range of colour and brightness

o Permanently lit or unlit pixels

A multimedia projector is an output device similar to an LCD monitor; however the lenses project intense light through its grid of LCD pixels.

Advantages are that it can be used with a much larger audience.

Disadvantage that it is expensive and has a fragile bulb.


Printers and plotters

Output devices that print characters and graphics on paper or other materials.

Inkjet printer – a device that prints precise characters and images on paper by spraying tiny droplets of ink.

Laser printer – high-speed device that prints precise characters and images on paper by using a laser to modify the electrostatic charge pattern that attracts toner particles to a drum, transfers the particles to a sheet of paper and fuses them on with heat rollers.

Dot matrix printer – a relatively slow, noisy device that prints characters by pins striking an inked ribbon against paper to make a pattern of relatively large dots.

Main advantages of a laser printer are the high resolution and rate of the output.

Disadvantages of laser printers are: o Reproduction of colour may not be precise as an inkjet printer

o Expensive to buy o Toner is toxic

Main advantage of an inkjet printer are: o High resolution o Good reproduction of colour

o Low purchase cost o Physically small and light

Disadvantages of an inkjet printer: o Slow rate of printing o High cost of ink per print o Water-soluble ink, which runs if prints get damp

Main advantage of a dot matrix printer is that it is robust, less likely to go wrong in dirty environments.

Disadvantages: o Low resolution o Noisy because of repeated impact of pins

o Low rate of printing


Loudspeakers

Many computer programs are designed to provide sound output. Has a digital-to-analogue converter (DAC).

People with visual impairments may have difficulty viewing a screen.

Text-to-speech software produces speech sounds from text on the screen or an image pop-up.

Speakers allow the user to listen to what is shown on the screen. Headphones are a version of speakers for personal use.

Often used in environments where other people should not hear the sounds produced. It might be because it would disturb their

concentration.

Actuators

An actuator is a device used by a computer to more machinery in a control system.

Output device but it doesn’t always provide output directly to the user.

Naturally pair up with sensors.

Irrigation system can turn on the water supply when the water gets too dry.

Automated systems use light bulbs to provide artificial light in a greenhouse for forcing plants to grow.

Light bulbs or LEDs are used as indicators of the status of equipment, including warning of faults.

An electrical heater is an actuator that supplies heat.

An electric motor is an actuator that provides rotary or linear movement.

A motorised pump forms an actuator that moves gases or liquids.

A buzzer is an audio signalling device that makes a rasping sound.

Specialised input and output devices

VR software creates a computer-generated, stereoscopic, 3-D view of an environment.

Main output devices are headsets or goggles.

Also can release an odour from its capsule.

Vibration actuators for wired gloves or VR suits capsule.


Internal memory and storage devices and their uses

A computer needs devices to keep the data that it processes.

Processing in rapid access internal memory (main memory). After processing, it stores the data for future use in slower-access

backing storage.

Internal memory

The processor uses internal memory to hold: o Program instructions that it’s executing o Data in use o Results of processing data.

Processor can access directly is immediate access store (IAS). Integrated circuits or chips, known as random access memory (RAM).

Processor can access the memory’s data in any order needed by the program.

Ensures that the processor has extremely rapid access to the data.

The processor can modify data from files and has ‘workspace’ for holding temporary results.

RAM chips hold data that are volatile. Means when we switch off the computer, the data are lost from the RAM.

Ram chips are installed in computers as plug-in, printed-circuit models and a total capacity of 1 or 2 GB.

ROM differs from RAM because the data it holds is non-volatile.

Once data is written on a ROM, they cannot be changed.

ROM stores a small start-up program at the processor’s default starting location.

It instructs the processor to read a larger program from ROM to RAM.

ROM is known as firmware because of its storage in hardware.

Measuring the size of memory

A computer stores and processes all data using binary equivalents.

A larger RAM capacity is better; it allows larger quantity of programs and

data.


Relationship between measurements

The table below outlines the relationship between bits (smallest) and terabytes (largest). Read each row of the table from left to right:

Relationship between measurement

Size Equal to

8 bits 1 byte

1024 bytes 1 kilobyte

1024 kilobytes 1 megabyte

1024 megabytes 1 gigabyte

1024 gigabytes 1 terabyte

Backing storage

Also known as auxiliary storage, stores programs and data for future use.

Backing storage is slower than access to internal memory.

The storage device is the machine that stores the data; the storage

medium.

Magnetic tape Principally used for backup of important files from the hard disk and for the long term storage and archiving of data.

Advantage

They are small, robust, and portable and provide low cost storage per GB.

Disadvantages They are very slow to write to and read from.

Serial access means all the data on the tape must be read before you can access the data you need.


External hard disks An external hard disk can store very large amounts of data, e.g. 1TB, and

can be plugged into your computer via a USB or FireWire port to provide extra storage. They're essentially the same as the hard disk in your computer but due to the casing are usable externally.

Advantage High capacity, e.g. 1TB or more so they can be used to backup data or

move large amounts of data between machines.

Disadvantages

They're often quite large and therefore inconvenient to carry around.

They have moving parts so are more likely to break, especially if dropped.

Memory sticks A memory stick is 'pen top' sized USB device and can be used in a similar

way to a floppy disk but it is inserted into the USB port - it is then seen by the computer as a removable drive. They typically come in sizes from 512MB to 32GB upwards depending on the price paid.

Advantages

Memory sticks can hold large quantities of data. They are extremely portable, so the user can take them wherever they

go.

They're durable, because they have no moving parts.

Disadvantage

Portable storage devices in general are more likely to be lost, stolen or damaged.

Memory Cards A memory card is a stamp-sized USB device and can be used in a similar

way to a floppy disk but it is inserted into either a memory card reader or a USB converter - it is then seen by the computer as a removable drive. They typically come in sizes from 1 GB to 32 GB upwards, depending on the price paid. There are many available memory card formats, but since 2010 the SD card became the more favoured format.

Advantages

Memory cards can hold large quantities of data.

They are extremely portable so the user can take them wherever they go.


Digital accessories such as compact cameras and mobile phones are able to read and write to memory cards allowing the user to transport large collections of photographs, songs or information with them.

They're durable because they have no moving parts.

Disadvantage

Memory cards, specifically the micro SD card, are the smallest storage devices available. This means they are more likely to be lost, stolen or damaged.

All computers do not come with memory card readers built in. Users will often be required to purchase a card reader or USB converter to view the data on a card.

External backing stores: optical discs

There are several different types of optical disc, although they all look pretty much the same.

CD (Compact Disc) Optical discs that use the same technology as music CDs. They store up

to 700MB of data. CDs can be used for multimedia applications such as encyclopaedias and can store pictures, sounds and video clips or anything else that will fit.

There are several formats on the market, such as:

CD-ROM - read only, the data is written to them before they are sold.

CD-R - meaning CD-Recordable, the user can write data to the CD once or fill it over time using multi-session (writing to the same disc on separate occasions).

CD-RW - meaning CD-ReWritable, the CD can be written and re-written to. Unlike multi-session discs, existing data can be overwritten.

DVD (Digital Versatile Disc) DVDs are the same physical size as CDs but hold much more data - a

single sided disc can hold up to 4.7GB. DVDs are commonly used for storing video so you will often see them measured in minutes, eg 4.7GB = 120 minutes.

There are several formats on the market, such as:

DVD-ROMs - read only, the data is written to them before they are sold.

DVD-R - meaning DVD-Recordable, the user can write data to the DVD once or fill it over time using multi-session.


DVD-RW - meaning DVD-ReWritable, the DVD can be written and re-written to. Unlike multi-session discs, existing data can be overwritten.

CD/DVD drives To read from and write data to CDs and DVDs you will need a suitable

drive. Today you can buy CD/DVD drives that are able to:

o read all CD and DVD formats o write to CD-R, CD-RW, DVD-R and DVD-RW o Data is written to and read from the discs using a laser.

Solid-state storage media

We refer this as non-volatile memory.

A USB flash drive is small and can hold several gigabytes of data. Advantage is that they are extremely small and portable and can store

large quantities if data. Can connect directly to a computer port.

No moving parts which makes them more robust than disk media.

Two main disadvantages: o More expensive per unit of data

o Flash-based devices have relatively limited number of write cycles

Comparing storage media

Storage capacity

Volume of data held

Rate of data access

Portability

Robustness

Cost


Mobile Phones Have embedded processors to manage a range of facilities. Access over cellular network:

o Microphone input

o Receiving SMS text messages o Multimedia messages – photos and video clips

o Internet – browsing, email

Recording videos and photos with built-in camera

Audio-recording

Storing contacts and media

Playing music Running game programs

Broadcasting radio

GPS navigation

Bluetooth

hardware notes for igcse computer studies 0420

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