Hardware and software2

3.1 Computer Architecture & Fetch-Execute
Cycle.

Computer Architecture
• Address bus – unidirectional
• Data bus – bi-directional
• Control bus – unidirectional and bi-directional

• Processor: The processor contains the Arithmetic and Logic Unit

(ALU)

• Control Unit: controls the operation of the memory, processor,

and input/ output devices.

The Fetch – Execute Cycle

1. PC contains the address of the next instruction to be fetched
2. This address is copied to the MAR via the address bus
3. The instruction of the address is copied into MDR temporarily
4. The instruction in the MDR is then placed in the CIR
5. The value in the PC is incremented by 1, pointing the next

instruction to be fetched.

6. The instruction is finally decoded and then executed.

3.2 Input Devices...

SCANNERS:
Two – dimensional Scanners:
• Used to input hard-copy documents
• The image is converted into an electronic from which can be stored in the

computer

o Document is placed on a glass panel
o A bright light illuminates the document
o A scan head moves across the document until the whole page is scanned. And image

of the document is produced and sent to a lens using a series of mirrors

o The lens focuses the document image
o The focused image now falls onto a change couple device (CCD) which consists of a

number of integrated circuits

o Software produces a digital image from the electronic form

Input Devices …

• Optical Character Recognition (OCR) is a software which converts scanned

documents into a text file format

• If the original document was a photo/image , then the scanned image

forms an image file such as JPEG

Three – dimensional Scanners
• 3D scanners can scan solid objects and produce a three – dimensional

image

• Scanners take image at several points, x , y and z (lasers, magnetic, white

light)

• The scanned images can be used in Computer Aided Design (CAD) or to a

3D printer to produce a working model

Input Devices …

Application of 2D Scanners at an Airport:
• Make use of (OCR) to produce digital images which represent the

passport pages

• Text can be stored in ASCII format
• The 2D photograph in the passport is also scanned and stored as jpeg

image

• The passenger’s face is also photographed using using a digital

camera and compared using face recognition software

• Key parts of the face are compared (distance between eyes, width of

nose)

Input Devices …

Barcode readers / scanners
• A barcode is a series of dark and light parallel lines of varying thicknesses
• The numbers 0-9 are each represented by a unique series of lines
• The left and right-hand sides of the barcode are separated using guard bars
• Allows barcode to be scanned in any direction

o

Barcode is read by a red laser or red LED

o Light is reflected back off the barcode; dark areas reflect little light which allows the

bars to be read

o Reflected light is read by sensors (photoelectric cells)
o Pattern is generated which is covered to digital

Input Devices …

Quick Response (QR) Codes
• Another type of barcode is the QR codes
• Made up of a matrix of filled-in dark squares on a light background
• Can hold more storage (7000 digits)
• Advantages of QR codes:

oNo need for the user to write down the website address
oQR codes can store website addresses

Input Devices …

Digital Cameras
• Controlled by a microprocessor which automatically adjusts the

shutter speed, focus the image, etc.

• Photo is captured when light passes through the lens onto a light

sensitive cell

• Cell is made up of pixels
• Number of pixels determines size of the file

Input Devices …

Keyboards
• Connected to computer with a USB connection or by wireless

connection

• Each character has an ASCII value and is converted into a digital signal
• Slow method
• Prone to errors

Input Devices …

Pointing devices
• Mouse/trackball

oTraditional; mechanical ball, connected by USB port

• Modern type; red LEDs to detect movement

Input Devices …

Microphones
• Used to input sound to a computer
• When a microphone picks up sound, a diaphragm vibrates producing

an electric signal

• The signal goes to a sound card and is converted into digital values

and stored in a computer

• Voice recognition, voice is detected and converted into digital

Input Devices …

Touchscreens
• Captive (medium cost tech)

o Made up of many layers of glass
o Creating electric fields between glass plates in layers
o When top layer of glass is touched, electric current changes
o Co-ordinates where the screen was touched is determined by an on-board microprocessor

• Infra-red heat (expensive)

o Use glass as the screen material
o Needs warm object to carry an input operation

• Infra-red optical (expensive)

o Uses glass as screen material
o Uses an array of sensors (grid form)
o Point of contract is based on which grid co-ordinate is touched

• Resistive (inexpensive)

o Upper layer of polyester, bottom layer of glass
o When the top polyester is touched, the top layer and bottom layer complete a circuit
o Signals are sent out which are interpreted by a microprocessor, to determine where the screen was touched

Input Devices …

Sensors
• Devices that read or measure physical properties
• Data needs to be converted to digital
• Analogue to Digital Converter (ADC) converts physical values into

digital

Input Devices …

Control of Street Lighting
• Light sensor sends data to the ADC
• Digitises data and sent to the microprocessor
• Microprocessor samples data every minute
• If data from sensor < value stored in memory:

oSignal sent from microprocessor to street lamp
oLamp switched on

Type of sensor

Type of data captured

Example of its ise

Acoustic

This type of sensors
measures the level
of sound in an
environment.

The sensors are used in
many applications that
involve sound. It can be
placed near a window and
constantly measure the
level of sound. If it
captures a reading that
shows a sudden increase
in sound, this could mean
that a window has been
broken and the building
may be at risk.

Accelerometer

This type of sensor
measures acceleration
forces. These may be static
forces, such as the
continual force of gravity.
They can also be dynamic
forces, such as those
created by movement and
vibrations.

These sensors are used in a wide
variety of devices. Mobile phones
use an accelerometer to know
which way up it is faced, to
automatically rotate the screen.
They can be used to monitor for
earthquakes, as they can capture
the initial vibrations. They can also
be used in cars to sense when a
crash has occurred, so that airbags
can be inflated.

Flow

This type of sensor
measures the
amount of liquid,
gas or steam that is
flowing through or
around a certain
environment.

These sensors are often used
in factories and sites such as
nuclear power plants. They
make sure that the liquid, gas
or steam flows at a constant
temperature through an
environment, such as a pipe.
This makes sure that pipes
don't rupture and break due
to too much flowing through
them.

Humidity

This type of
sensor measures
the level of
moisture in the
immediate
atmosphere

These sensors can be used in
farming and agriculture to
make sure that the air in areas
such as greenhouses has the
correct level of moisture to
provide the best growing
conditions for the fruits and
vegetables. They can also be
used in places such as art
galleries, to make sure that
the humidity level is constant.
Too much or too little can ruin
paintings.

Gas

This type of sensor
measures the presence
and concentration of a gas
within the immediate
atmosphere.

These sensors can be used in
people's homes. They can be
set to measure a certain gas,
such as carbon monoxide.
They constantly capture the
data in the immediate
atmosphere to see if too
much carbon monoxide is
present, which could
endanger the health of
anyone living in the home.

Infra-red

This type of sensor
measures infra-red
radiation. This type of
radiation can be emitted in
different amounts by both
objects and people.

These sensors can also be
used in security systems. This
can be done in two different
ways. The device containing
the sensor can emit infra-red
radiation and when this
bounces back to the device,
the readings can show how far
the distance it has travelled. It
can also show if there is an
intruder present. The sensor
can also operate by capturing
the infra-red radiation emitted
by the intruder

Level

This type of sensor
measures whether a
substance, such as a
liquid, is at a certain level
or amount.

These sensors can be used in
a car to make sure that
essential liquids, such as oil
and fuel, do not get too low.

Light

This type of sensor
measures the ambient
light in a certain
environment. It can
also measure the
presence of a direct
light, such as a laser
beam.

These sensors can be used
in automatic lighting
systems. Streetlights can
be fitted with a light sensor
that will allow the light to
turn on in the evening,
when it becomes darker.

Magnetic Field

Measures the presence
of a magnetic field
emitted by an object.

Used to count cars
passing through an area,
such as a car park, by
detecting disruptions in
the Earth's magnetic field

Moisture

Measures the amount of
water present in a
substance, such as soil.

Used in farming and
agriculture to ensure
optimal water levels for
growing fruits and
vegetables.

pH

Measures the pH level of
a substance

Used by environmental
agencies to monitor
pollution levels in lakes
and rivers

Pressure

Measures the force of
pressure applied to the
sensor or device. Can be
caused by solids, liquids, or
gases.

Used in security systems to
detect intruders by
monitoring pressure
changes when a window or
door is opened.

Proximity

Measures how close an
object is to the sensor by
emitting electromagnetic
radiation or a field and
measuring what returns.

Used in manufacturing
robots to help them
navigate around objects in a
factory.

Temperature

Measures the temperature
of an object or substance
either directly or from the
surrounding environment

Used in air conditioning
systems to maintain room
temperature.

Activity 1:

Qn1. List down real-life examples of automated systems with
their relevant sensors.

Example:

Smart Home Thermostat:
•Sensor: Temperature sensor

•Function: Automatically adjusts heating or cooling based on the measured room
temperature

Automatic Door opener:
•Sensor: Motion Sensor

•Function: Detects movement near the doorway and automatically opens the door.

Output Devices

PRINTERS:
Inkjet Printers
• Used to print one-off pictures and documents
1.

Data from document sent to printer driver

2.

Printer driver ensures data is in correct format

3.

Check made by printer driver that chosen printer is available

4.

Data is sent to printer, stored in a temporary memory (printer buffer)

5.

Sheet of paper is fed; sensor detects if paper is available in paper tray

6.

Print head moves across paper printing text/image, four ink colours sprayed in
exact amount

7.

Paper is advanced so next line is printed

8.

Repeated until buffer is empty

9.

Once it is done, printer send an interrupt to the processor (request for more
data to be sent)

Output Devices …
Laser Printers
• Used to print flyers, high quality
• Use dry powder ink (toner) and static electricity to produce text and images
• Prints the whole page in one go
1.

(steps 1-4 same as inkjet)

2.

Printing drum is given a positive charge; as the drum rotates, a laser beam is scanned
across it removing the positive charge leaves negatively charged areas which match
the text/image

3.

Drum is then coated with positively charged toner, it only sticks to negatively charged
parts of the drum

4.

A negatively charged sheet is rolled over the drum

5.

Toner on the drum now sticks to the paper to produce copy of page

6.

Paper finally goes through a fuser (set of heated rollers); heat melts the ink so it is
permanent

7.

Discharge lamp removes all electric charge from the drum, ready to print next page

Output Devices …

3D Printers
• Used for models of cars
• Produce solid objects that work
• Built up layer by layer, using powdered resin, ceramic powder
• A design is made using Computer-aided Design (CAD)

Output Devices …

2D and 3D Cutters
• 3D cutters can recognise objects in x, y, z direction
• 3D laser cutters can cut; glass, crystal, metal, wood

Actuators
• Used in many control applications involving sensors and devices (ADC

and DAC)

Output Devices …

Loudspeakers/Headphones
• Sound is produced by passing the digital data through a DAC then

through amplifier and then emerges from loudspeaker

• Produced by voltage differences vibrating a cone in the speaker at

different frequencies

Output Devices …

LCD and LED Monitors
• Front layer of monitor is made up of Liquid Crystal Display (LCD),

these tiny diodes are grouped together in threes as pixels (LCD
doesn’t emit any light)

• LCD monitors are back lit using Light Emitting Diode (LED) because:

oLEDs reach their maximum brightness immediately
oLEDs sharpens image (higher resolution), CCFL has yellow tint
oLEDs improve colour image
oMonitors using LED are much thinner than CCFL
oLEDs consume very little power

Output Devices …

LCD and LED Monitors (continues…)
• Before LEDs, LCD monitors were backlit using CCFL
• CCFL uses two fluorescent tubes behind the LCD screen which

supplies the light source

Output Devices …

LIGHT PROJECTORS:
• Two common types of light projectors:

oDigital Light Projector (DLP)
oLCD Projector

• Projectors are used to project computer output onto larger

screens/interactive whiteboards

Output Devices …

Digital Light Projectors (DLP)
• Uses millions of micro mirrors
• The number of micro mirrors and the way they are arranged on the DLP

chip determines the resolution of the image

• When the micro mirrors tilt towards the light source they are on
• When the micro mirrors tilt away from the light source they are off
• This creates a light or dark pixel on the projection screen
• A bright white light source passes through a colour filter on its way to the

DLP chip

• White light splits into primary colours

Output Devices …

LCD Projectors
• Older technology than DLP
• A powerful beam of white light is generated from a bulb
• This beam of light is then sent to a group of chromatic coated mirrors;

these reflect the light back at different wavelengths

• When the white light hits the mirrors, the reflected light has wavelengths

corresponding to red, green and blue

• These three different light pass through three LCD screens; these screens

show the image to be projected as millions of pixels in grayscale

• When the coloured light passes through the LCD screens, a red, green and

blue version of the grey image emerges

• Finally, the image passes through the projector lens onto the screen.

Data Storage

Memory, Storage Devices & Media
You need to store data in a computer system on a constant basis. This
might be temporarily, whilst it is being processed, or on a more
permanent basis for future use.
- For this purposes, there are two main categories of storage that exist

in a computer, they are

- Primary storage and
- Secondary storage.

Data Storage…

PRIMARY STORAGE:
- This is a category of storage that is directly accessed by the CPU.
- There are two main types of primary storage;

• Random Access Memory (RAM)
• Read Only Memory (ROM)

Primary Storage…

Random Access Memory (RAM)
• Features of RAM

oVolatile/temporary memory (contents lost if RAM is turned off)
oUsed to store; data, files
oIt can be written to or read from and the contents from the memory can be

changed

• Larger the size of the RAM, faster the computer will operate
• RAM never runs out of memory, continues to run slow
• As RAM becomes full, the processor has to continually access the

hard drive to overwrite old data on RAM with new data.

Primary Storage…

Read Only Memory (ROM)
• Features of ROM

oNon-volatile/permanent memories (contents remain even when ROM is

turned off)

oUsed to store start up instruction (basic input/output systems)
oData/contents of a ROM chip can only be read, cannot be changed

SECONDARY STORAGE:

Hard Disk Drives (HDD) (magnetic storage)
• Data is stored in a digital format on the magnetic surface of the disks

(platter)

• Number of read/write heads can access all of the surfaces of the disk
• Each platter will have two surfaces which can be used to store the

data

• Data is stored on the surfaces in sectors and tracks
• HDD have very slow data access compared to RAM

Secondary Storage…
Solid-State Storage (SDD)
• No moving parts and all data is received at the same time (not like HDD)
• Store data by controlling the movement of electrons within NAND chips, as

1s and 0s

• Non-volatile rewritable memory
• Benefits of using SDD rather than HDD:

o More reliable (no moving parts)
o Considerably lighter (suitable for laptops)
o Lower power consumption
o Run much cooler than HDDs
o Very thin
o Data access if faster than HDD

• Drawback – questionable longevity (20GB per day)

OFF-LINE STORAGE

CD/DVD Disks (Optical storage)
• Laser (red) light is used to read and write data in the surface of the

disk

• Use a thin layer of metal alloy to store data
• Both systems use a single, spiral track which runs from the centre of

the disk to the edge

• DVD uses Dual-Layering which increases the storage capacity (two

individual recoding layers)

OFF-LINE STORAGE…

Blu-ray Disks (Optical storage)
• Uses blue laser to carry out read and write operations
• Wavelength of laser light is less than CD and DVD (stores up to five

times more data than DVD)

• Automatically come with secure encryption (prevent piracy and

copyright infringement)

• Used as back-up systems

OFF-LINE STORAGE…

USB Flash Memories ( solid state storage)
• Very small, lightweight suitable from transferring files
• Small back-up devices for photo, music
• Solid state so need to be treated with care

Virtual Memory

• It is called virtual memory, as unlike physical storage , it isn’t a component

that you can see or touch.

• Virtual memory is a type of memory that is created for temporary use.
• It is created as an extension to RAM
• When RAM becomes full, it needs some extra help! This is where virtual

memory can help.

• Virtual memory is created in a computer system with a hard drive

component.

• A section of that hard drive is partitioned off and is effectively an extra bit

for RAM instead.

Virtual Memory…

• When RAM gets full, the computer system can transfer some data to

the virtual memory to be held there until it is needed.

• The data that is transferred to the virtual memory is collected in a

structure called a page (a unit of data)

• These pages of data are transferred to the virtual memory to make

sure there is enough room in the RAM for the immediate data that is
being processed.