1.3 HARDWARE

REVISION 9608 – SECTION 1 1

INPUT, OUTPUT, STORAGE DEVICES QUESTION 1 Sensors are one type of input device. For each of the following situations, name a different sensor that could be used. (i) air conditioning in an office building (ii) maintaining correct growing conditions in a greenhouse (iii) detecting an intruder in a building ANSWER 1 (i) temperature/thermistor (ii) moisture, humidity, light/photodiode, temperature, pH (iii) sound/acoustic, infrared, pressure, motion, microwave QUESTION 2 Name the most suitable input or output device for each of the following uses. Give a different device in each case. ANSWER 2

QUESTION 3

Most computers use Universal Serial Bus (USB) ports to allow the attachment of devices. Describe two benefits of using USB ports. ANSWER 3

devices automatically detected and configured when first attached/plug and play

it is nearly impossible to wrongly connect a device

USB has become an industrial standard

supported by many operating systems

1.3 HARDWARE

REVISION 9608 – SECTION 1 2

USB 3.0 allows full duplex data transfer

later versions are backwards compatible with earlier USB systems

allows power to be drawn to charge portable devices QUESTION 4 A computer system in a control room is used to monitor earthquake activity. An earthquake zone has a number of sensors to detect seismic activity. The system detects when seismic activity is greater than 3 on the Richter Scale. Whenever this happens, a printer in the control room prints a report. (i) Identify the steps that are required in this monitoring system. (ii) When the system detects high activity, operators may need to respond rapidly. A printer is

useful for hard copies, but may not be the best way to inform operators. Give a reason why. (iii) Name an alternative output device for this monitoring system and give a reason for your choice.

Output device - Reason for choice - ANSWER 4 (i) – sensors send signals / data to a computer – data / signal converted to digital (using an ADC)

– computer calculates the activity value based on sensor signal strength / data – if calculated value > 3,

– determine location of sensor – build up a map of seismic activity – location and magnitude sent to printer – … via USB port / wireless link – monitoring is continuous QUESTION 5 Examples of primary and secondary storage devices include:

hard disk

DVD-RW

flash memory For each device, describe the type of media used. ANSWER 5 Hard disk – magnetic (storage media) DVD-RW – optical (storage media) Flash memory – solid state (memory device) QUESTION 6 (a) Describe how a laser mouse operates. (b) The following table shows a list of five statements which describe the stages when a page is

printed using an inkjet printer. Put each statement in the correct sequence by writing the numbers 1 to 5 in the right-hand column.

1.3 HARDWARE

REVISION 9608 – SECTION 1 3

ANSWER 6 (a) – laser/light shines onto a surface – through a (polished) ring at the base – the light is reflected from the surface through the ring – sensor detects reflected light – capturing details/photograph of surface (under the ring) – at about 1500 times per second – as the mouse moves the sensor detects changes in the surface detail/photograph – which are translated into movement (change of x and y co-ordinates) – the computer/software updates the position of the cursor on the screen (b) QUESTION 7 What is a Computer System? ANSWER 7

A computer is an electronic machine that accepts data, stores and processes data into information.

The computer is able to work because there are instructions in its memory directing it.

Instructions that direct the computer are called software or computer program.

The physical parts of the computer that you can see and touch (keyboard, monitor, mouse, etc.) are called hardware.

There are 4 categories of computer hardware: o Input devices: used to enter data into the computer. o Processing devices: manipulate the data. o Storage devices: store data and program. o Output devices: show results of the process.

QUESTION 8 Briefly explain the term ‘Keyboard’. ANSWER 8

The keyboard is one of the most popular ways of inputting information into a computer.

The basic mechanical keyboard relies on keys being pressed down to complete an electrical circuit.

1.3 HARDWARE

REVISION 9608 – SECTION 1 4

This circuit then transmits a binary signal (using ASCII) to the computer to represent the key pressed.

QUESTION 9 Briefly explain the term ‘Scanner’. ANSWER 9

A scanner creates a digital photograph of a paper document.

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

Each sensor produces an analogue signal that depends on the intensity of the light it receives.

The scanner’s embedded computer repeatedly scans the signals from the sensors as they move across the document.

The embedded computer then digitizes, processes them and sends them to the computer. QUESTION 10 Briefly explain the following 3 types of Scanner: (i) Fingerprint scanner (ii) Retina scanner (iii) Iris scanner ANSWER 10 (i) Finger Scanner:

The ridges and troughs on a person’s finger and toes are unique to that person.

Using a scanner a finger print pattern can be recorded and compared to others on a database, allowing a computer to match finger prints from crimes to a suspect, or to allow people into restricted areas.

(ii) Retina Scanner:

Retina scanners are used to record the pattern of blood vessels at the back of someone’s eye.

As every has a different pattern of vessels, then retina scanners can be used to uniquely identify people and are very difficult to fake.

(iii) Iris Scanner:

By taking a picture of the blood vessels and colouring of someone’s eye, we can get a unique pattern that can be used to identify individuals.

People might try and circumvent this by using contact lenses. QUESTION 11 Briefly explain the term ‘Trackerball Mouse’. ANSWER 11

A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball.

The user rolls the ball with the thumb, fingers, or the palm of the hand to move a pointer. QUESTION 12 Briefly explain the term ‘Laser Mouse’. ANSWER 12

A laser mouse is a type of optical mouse that uses laser light to detect mouse movement.

1.3 HARDWARE

REVISION 9608 – SECTION 1 5

Like all optical mice, the laser mouse has no moving parts inside. QUESTION 13 Briefly explain the term ‘Sensor’. ANSWER 13

A sensor is a device that detects and responds to some type of input from the physical environment.

The specific input could be light, heat, motion, moisture, pressure, or any one of a great number of other environmental phenomena.

The output is generally a signal that is converted to human-readable display at the sensor location or transmitted electronically over a network for reading or further processing.

Following is the list of commonly used sensors: o Temperature o Hall effect o Gas o Pressure o Moisture o Humidity o Ph/Acidity/Alkalinity o Motion/Infra-Red

QUESTION 14

State the advantages and disadvantage of using Sensors. ANSWER 14

Advantages: 1. They can collect data far more frequently than a person. 2. They are more reliable than a person, who may forget to take readings. 3. They are more accurate than a person who may misread the signal. 4. They can collect data from places where it is not possible for a person to go such as inside a

chemical or nuclear reaction vessel. Disadvantages: 1. They may need a power supply to work 2. They may need regular calibration to check their accuracy. QUESTION 15 Briefly explain the term ‘Temperature Sensor’. ANSWER 15

A temperature sensor is a device, typically, a thermocouple or RTD, that provides for temperature measurement through an electrical signal.

A thermocouple (T/C) is made from two dissimilar metals that generate electrical voltage in direct proportion to changes in temperature.

QUESTION 16 Briefly explain the term ‘Pressure Sensor’. ANSWER 16

A pressure sensor produces a signal that depends on the pressure to which it is exposed.

Pressure sensor can be used in many appliances such as automatic blood pressure monitor.

1.3 HARDWARE

REVISION 9608 – SECTION 1 6

Pressure sensor can also control the pressure of gases or liquids in chemical reaction vessel. QUESTION 17 Briefly explain the term ‘Hall Effect Sensor’. ANSWER 17

A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field.

Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications.

QUESTION 18 Briefly explain the term ‘Gas Sensor’. ANSWER 18

A gas detector is a device that detects the presence of gases in an area, often as part of a safety system.

This type of equipment is used to detect a gas leak and interface with a control system so a process can be automatically shut down.

QUESTION 19

Briefly explain the term ‘Moisture / Humidity Sensor’. ANSWER 19

A moisture sensor measures the quantity of water contained in a material, such as soil on a volumetric or gravimetric basis. To obtain an accurate measurement, a soil temperature sensor is also required for calibration.

A humidity sensor (or hygrometer) senses, measures and reports the relative humidity in the air. It therefore measures both moisture and air temperature. Relative humidity is the ratio of actual moisture in the air to the highest amount of moisture that can be held at that air temperature.

QUESTION 20 Briefly explain the term ‘PH/Acidity/Alkalinity Sensor’. ANSWER 20

A pH Meter is a scientific instrument that measures the hydrogen-ion concentration (orpH) in a solution, indicating its acidity or alkalinity.

The pH meter measures the difference in electrical potential between a pHelectrode and a reference electrode.

QUESTION 21 Briefly explain the term ‘Infrared Sensor’. ANSWER 21

An infrared sensor is an electronic device that emits and/or detects infrared radiation in order to sense some aspect of its surroundings.

Infrared sensors can measure the heat of an object, as well as detect motion. QUESTION 22 Briefly explain the term ‘Laser Printer’.

1.3 HARDWARE

REVISION 9608 – SECTION 1 7

ANSWER 22

A printer linked to a computer producing good-quality printed material by using a laser to form a pattern of electrostatically charged dots on a light-sensitive drum, which attract toner (or dry ink powder).

The toner is transferred to a piece of paper and fixed by a heating process. QUESTION 23 Briefly explain the term ‘Inkjet Printer’. ANSWER 23

An inkjet printer uses a print head to propel differently sized droplets of ink, measuring just picolitres, from a number of fine nozzles onto a sheet of paper.

The printhead scans from side to side on stabilizer bar and rollers feed the paper forward. QUESTION 24 Briefly explain the term ‘Speakers’. ANSWER 24

Speakers are one of the most common output devices used with computer systems.

The purpose of speakers is to produce audio output that can be heard by the listener.

Speakers are transducers that convert electromagnetic waves into sound waves.

Speakers use magnets to convert electricity into sound waves.

This is a basic principle of physics.

Sound is made when an object makes the particles around it vibrate.

These vibrations travel the air and reach your ears.

Our brain interprets this motion as sound.

High frequencies of sound are made when the wavelength of the vibrations are close together.

Low frequencies occur when they are farther apart.

The amplitude of the vibrations causes the level of volume you hear.

To make these vibrations, speakers have a set of magnets.

One of them is called the permanent magnet.

It doesn’t move or change polarity and is made of a magnetic metal like iron.

The other magnet is an electromagnet.

It is a coil of metal wire like copper or aluminum.

When an electric current is sent through the electromagnet, it is either attracted to or repelled away from the permanent magnet.

The polarity of the coil can be reversed depending on the current.

This back and forth movement causes the diaphragm or cone to vibrate, because it is connected to the magnetic coil.

This is the sound that you hear. QUESTION 25

Briefly explain the term ‘Actuators’. ANSWER 25

An actuator is an output device but it does not always provide output directly to the user.

It can change some physical value in response to a signal from an automated system or control system.

Actuators naturally pair up with sensors, which can provide feedback to the control program about the effects of its actuators.

1.3 HARDWARE

REVISION 9608 – SECTION 1 8

QUESTION 26 Briefly explain the term ‘Backing Storage’. ANSWER 26

Backing storage stores programs and data for future use.

In order to store data while the electricity is switched off or unavailable storage must be non-volatile.

Access to backing store is slower than internal memory.

Operating systems and program files are loaded into RAM form backing storage when required for execution.

QUESTION 27

Explain the difference between storage device and storage medium. ANSWER 27

It is important to distinguish between a storage device and storage medium.

The storage device is the machine that stores data.

The storage medium is the material on which the device stores data.

There are 3 different types of backing storage device:

1. Magnetic storage device 2. Optical storage device 3. Sold state storage device

QUESTION 28 Briefly explain the term ‘Magnetic Storage’. ANSWER 28

Data storage is a critical component of any computer system.

Magnetic storage is one of the most affordable ways to store large amounts of data and has been implemented using magnetic tape, floppy disks and hard disk drives.

QUESTION 29 Briefly explain the term ‘Hard Disk’. ANSWER 29

Hard disk is a data storage device used for storing and retrieving digital information using one or more rigid ("hard") rapidly rotating disks (platters) coated with magnetic material.

QUESTION 30 Briefly explain the term ‘Optical Media’. ANSWER 30

Optical media refers to discs that are read by a laser.

This includes CD-ROMs, DVD-ROMs, and all the variations of the two formats -- CD-R, CD-RW, DVD-R, DVD+R, Blu-ray, and many others.

1.3 HARDWARE

REVISION 9608 – SECTION 1 9

QUESTION 31 Briefly explain the term ‘USB’. ANSWER 31

A Universal Serial Bus (USB) is a common interface that enables communication between devices and a host controller such as a personal computer (PC).

It connects peripheral devices such as digital cameras, mice, keyboards, printers, scanners, media devices, external hard drives and flash drives.

QUESTION 32 Briefly explain the term ‘USB’. ANSWER 32

A memory card or flash card is an electronic flash memory data storage device used for storing digital information.

These are commonly used in portable electronic devices, such as digital cameras, mobile phones, laptop computers, tablets, MP3 players and video game consoles.

QUESTION 33

DVD-RAM and Flash Memory are 2 examples of storage devices. Describe two differences in how they operate. ANSWER 33 DVD-RAM

data is stored/written using lasers/optical media

DVD-RAM uses phase changing recording, in which varying laser intensities cause targeted areas in the phase change recording layer to alternate between an amorphous and a crystalline state.

uses a rotating disk with concentric tracks

allows read and write operation to occur simultaneously

1.3 HARDWARE

REVISION 9608 – SECTION 1 10

FLASH MEMORY

most are NAND-based flash memory

there are no moving parts

uses a grid of columns and rows that has two transistors at each intersection

one transistor is called a floating gate

the second transistor is called the control gate

memory cells store voltages which can represent either a 0 or a 1

essentially the movement of electrons is controlled to read/write

not possible to over-write existing data; it is necessary to first erase the old data then write the new data in the same location

1.3 HARDWARE

REVISION 9608 – SECTION 1 11

MAIN MEMORY QUESTION 1

Briefly describe the term ‘RAM’. ANSWER 1

This is a volatile memory.

Contents are lost when the computer is switched off.

A user can write or delete data as well as read the contents.

Before a program can be ran it must first be loaded into RAM which allows the CPU to access the program.

QUESTION 2 Briefly describe the term ‘ROM’. ANSWER 2

ROM holds the instructions for starting up the computer.

This type of memory can only be read and cannot be altered (delete or written).

It is called non-volatile.

It doesn’t lose its contents when the computer is switched off. QUESTION 3

Briefly describe the term ‘Static RAM (SRAM)’. ANSWER 3

SRAM is a type of memory that is faster and more reliable than the more common DRAM (dynamic RAM). The term static is derived from the fact that it doesn't need to be refreshed like dynamic RAM. QUESTION 4 Briefly describe the term ‘Dynamic RAM (DRAM)’. ANSWER 4

DRAM is a type of physical memory used in most personal computers. The term dynamic indicates that the memory must be constantly refreshed (reenergized) or it will lose its contents. QUESTION 5 Give three differences between Dynamic RAM (DRAM) and Static RAM (SRAM). ANSWER 5

SRAM is static while DRAM is dynamic

SRAM is faster compared to DRAM

SRAM consumes less power than DRAM

SRAM uses more transistors per bit of memory compared to DRAM

SRAM is more expensive than DRAM

Cheaper DRAM is used in main memory while SRAM is commonly used in cache memory

1.3 HARDWARE

REVISION 9608 – SECTION 1 12

QUESTION 6 There are two types of RAM: dynamic RAM (DRAM) and static RAM (SRAM). Five statements about DRAM and SRAM are shown below. Draw a line to link each statement to the appropriate type of RAM. ANSWER 6

1.3 HARDWARE

REVISION 9608 – SECTION 1 13

LOGIC GATES AND LOGIC CIRCUITS QUESTION 1

A system is monitored using sensors. The sensors output binary values corresponding to physical conditions, as shown in the table:

The outputs of the sensors form the inputs to a logic circuit. The output from the circuit, X, is 1 if any of the following three conditions occur: either oil pressure >= 3 bar and temperature >= 200°C or oil pressure < 3 bar and rotation > 1000 rpm or temperature >= 200°C and rotation > 1000 rpm (a) Draw a logic circuit to represent the above system.

1.3 HARDWARE

REVISION 9608 – SECTION 1 14

(b) Complete the truth table for this system.

ANSWER 1 (a)

(b)

1.3 HARDWARE

REVISION 9608 – SECTION 1 15

QUESTION 2 (a) Three digital sensors A, B and C are used to monitor a process. The outputs from the sensors are

used as the inputs to a logic circuit. A signal, X, is output from the logic circuit:

Output, X, has a value of 1 if either of the following two conditions occur:

sensor A outputs the value 1 OR sensor B outputs the value 0

sensor B outputs the value 1 AND sensor C outputs the value 0 Draw a logic circuit to represent these conditions.

(b) Complete the truth table for the logic circuit described in part (a).

1.3 HARDWARE

REVISION 9608 – SECTION 1 16

(c) Write a logic statement that describes the following logic circuit.

ANSWER 2 (a)

(b) c) ((A is NOT 1 AND B is 1) OR (B is NOT 1 OR C is 1)) AND C is NOT 1

1.3 HARDWARE

REVISION 9608 – SECTION 1 17

QUESTION 3 (a) Complete the table to show the outputs for the possible inputs to this circuit.

(b) State a possible use for this circuit in a processor. ANSWER 3 (a)

(b) It adds together two single bits/a half adder.