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Computer science GCSE > Chapter 3: Hardware > Flashcards

Chapter 3: Hardware Flashcards

1
Q

What is the central processing unit responsible for?

A

The central processing unit (CPU) is responsible for the execution or processing of all the instructions and data in a computer

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2
Q

What is an integrated circuit?

A

Usually a chip made from a semi-conductor material which carries out the same tasks as a larger circuit made from individual components

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3
Q

What is von Neumann architecture?

A

A type of computer architecture which introduced the concept of the stored program in the 1940s

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4
Q

What is the Arithmetic & Logic Unit (ALU)?

A

The component of the CPU that carries out all the arithmetic and logical operations

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5
Q

What is an accumulator (ACC)?

A

Temporary general-purpose register that stores numerical values at any part of a given operation

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6
Q

What is a memory address register (MAR)?

A

A register that stores the address of the memory location currently being read from or written to

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7
Q

What is a current instruction register (CIR)?

A

A register that stores the current instruction being decoded and executed

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8
Q

What is a memory data register (MDR)?

A

A register that stores data that has just been read from memory or data that is about to be written to memory

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9
Q

What is a program counter (PC)?

A

A register that stores the address where the next instruction to be read can be found

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10
Q

What is the control unit?

A

The component of a computer’s CPU that ensures synchronisation of data flow and programs throughout the computer by sending out control signals along the control bus.

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11
Q

What does a system clock do?

A

Produce timing signals on the control bus to ensure synchronisation takes place

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12
Q

What is a clock cycle?

A

Clock speeds are measured in terms of GHz; this is the vibrational frequency of the system clock which sends out pulses along the control bus; for example, a 3.5 GHZ clock cycle means 3.5 billion clock cycles a second.

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13
Q

What is the immediate access store (IAS)?

A

Memory that holds all data and programs needed to be accessed by the control unit

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14
Q

What is a backing store?

A

A secondary storage device (such as HDD or SSD) used to store data permanently even when the computer is powered down

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15
Q

What is a register?

A

A temporary component in the CPU which can be general or specific in its use; it holds data or instructions as part of the Fetch-Decode-Execute cycle

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16
Q

What is an address?

A

A label for a memory location used by the CPU to track data

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17
Q

What is a memory location?

A

A numbered place in memory where values can be stored?

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18
Q

What is a system bus?

A

A connection between major components in a computer that can carry data, addresses or control signals

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19
Q

What is an address bus?

A

A system bus that carries the addresses throughout the computer system

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20
Q

What is a data bus?

A

The system bus that carries signals from control unit to all other computer components

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21
Q

Definition of unidirectional

A

Can travel in one direction only; used to describe data

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22
Q

Definition of bidirectional

A

Can travel in both directions; used to describe data

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23
Q

What is a word (in computer science)?

A

A group of bits used by a computer to represent a single unit; for example, modern computers often use 64-bit word lengths

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24
Q

What does overclocking mean?

A

Changing the clock speed of a system clock to a value higher than the factory/ recommended setting

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25
Q

What is a core?

A

A unit on a CPU made up of an ALU, control unit and registers; a CPU may contain a number of cores

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26
Q

What is a dual core?

A

A CPU containing two cores

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27
Q

What is a quad core?

A

A CPU containing four cores

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28
Q

What is Fetch-Execute-Decode?

A

A cycle in which instructions and data are fetched from memory, decoded and finally executed

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29
Q

What is the Basic Input/Output System (BIOS)?

A

A suite of programs on firmware that are used to perform the initialisation of a computer system during the boot-up process

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30
Q

What is opcode?

A

Part of a machine code instruction that identifies what data is to be used

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31
Q

What is operand?

A

Part of a machine code instruction that identifies what data is to be used

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32
Q

What is an instruction set?

A

The complete set of machine code instructions used by a particular microprocessor

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33
Q

What is an embedded system?

A

A combination of hardware and software designed to carry out a specific set of functions

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34
Q

What is a barcode?

A

A series of dark and light lines of varying thickness used to represent data; the code has to be scanned using laser or LED light source

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35
Q

What is the key field?

A

The field that uniquely identifies a record in a file

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36
Q

What is a quick response (QR) code?

A

A matrix of dark and light squares which represent data; the pattern can be read and interpreted using a smartphone camera and QR app

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37
Q

What is a frame QR code?

A

A type of QR code that includes a space for advertising

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38
Q

What is a DAC (digital to analogue converter)?

A

A device that converts digital data into electric currents that can drive motors, actuators and relays, for example

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39
Q

What is an ADC (analogue to digital converter)?

A

A device that converts analogue data (for example, data read from sensors) into a form understood by a computer

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40
Q

What is a charge couple device (CCD)?

A

A light sensitive cell made up of millions of tiny sensors acting as photodiodes

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41
Q

What is a virtual keyboard?

A

An onscreen keyboard which uses the features of the touch screen to emulate a physical keyboard

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42
Q

What is a touch screen?

A

A screen that allows the user to select of manipulate a screen image using the touch of a finger or stylus; touch screens most frequently use capacitive, infra-red or resistive technology

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43
Q

What is repetitive strain injury (RSI)?

A

Pain felt in the muscles, nerves and tendons caused by a repetitive action (for example, excessive clicking of a mouse button over a period of time)

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44
Q

What is an optical mouse?

A

A pointing device that uses a red LED to track the movement of the device and then relays its coordinates to a computer

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45
Q

What is a pointing device?

A

An input device that allows the user to control the movement of an onscreen cursor or to allow onscreen selection by clicking a button on the device

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46
Q

What is a complementary metal oxide semi-conductor (CMOS)?

A

A chip that generates an electric current (or pulses) when light falls on its surface

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47
Q

What is a digital signal processor (DSP)?

A

A processor that calculates, for example, the coordinates of a pointing device based on the pulses of electricity received

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48
Q

What is optical character recognition?

A

Technology that can convert hard copy text or images into a digital format to be stored in a computer memory

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49
Q

What is computer aided design (CAD)?

A

Software used to create drawings (for example, to send to a 3D printer or to produce blue-prints of a microprocessor design)

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50
Q

What is a computed tomographic (CT) scanner?

A

Technology that can create a 3D image of a solid object by slicing up the object into thin layers (tomography)

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51
Q

What is a capacitive touch screen?

A

A type of touch screen that uses the change in the screen’s capacitance (the ability to store an electrical charge) when it is touched by a finger or stylus

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52
Q

What is an infra-red touch screen?

A

A type of touch screen that uses infra-red beams and sensors to detect where the screen has been touched

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53
Q

What is a resistive touch screen?

A

A type of touch screen that uses two conductive layers which make contact where the screen has been touched

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54
Q

What is an actuator?

A

An output device that converts electrical energy into mechanical movement

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55
Q

What is a digital micromirror device (DMD)?

A

A chip that uses millions of tiny mirrors on its surface to create a video display

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56
Q

What is thermal bubble?

A

Inkjet printer technology whereby tiny resistors create heat and form an ink bubble which is ejected onto paper in an inkjet printer

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57
Q

What is a piezoelectric crystal?

A

A crystal located in an ink reservoir within an inkjet printer; the crystal vibrates and forces ink out onto paper

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58
Q

What is direct 3D printing?

A

A 3D printing technique in which the print head move in the x, y and z directions

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59
Q

What is binder 3D printing?

A

A 3D printing method that uses a two-stage pass; the first stage uses dry powder and second stage uses a binding agent

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60
Q

What is a cathode?

A

A negative electrode

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61
Q

What is cache?

A

Cache is temporary memory using static RAM to hold frequently used data / instruction by the CPU thereby increasing CPU performance. More generally, cache means any area of storage used to quickly access frequently-used data - other examples include web cache, database cache, DNS cache

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62
Q

What is an anode?

A

A positive electrode

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63
Q

What is organic LED (OLED)?

A

A light-emitting diode that uses the movement of electrons between a cathode and an anode to produce an on-screen image; it generates its own light so no backlighting is required

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64
Q

What is a loudspeaker?

A

An output device that converts electric current into sound

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65
Q

Function of memory

A

Stores program operations and data during the execution cycle of a program.

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66
Q

What is random access memory (RAM)?

A

Primary memory than can be written to or read from

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67
Q

What is read only memory (ROM)?

A

Primary memory that cannot be written to (changed) and can only be read

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68
Q

What is dynamic RAM (DRAM)?

A

A type of RAM chip that needs to be constantly refreshed

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69
Q

What is static RAM (SRAM)?

A

A type of RAM chip that uses flip flops and doesn’t need to be constantly refreshed

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70
Q

What does volatile mean?

A

Describes memory that loses its contents when the power is turned off

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71
Q

What does refresh mean?

A

Recharge every few seconds in order to maintain charge; for example with a device such as a capacitor

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72
Q

What does flip flop mean?

A

Electronic circuit with only two stable conditions

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73
Q

What is latency?

A

The lag in a system; for example, the time it takes to find a track on a hard disk, which depends on the time it takes for the disk to rotate around to its read-write head

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74
Q

What is SSD endurance?

A

The total guaranteed number of times data can be written to or read from a solid state drive (SSD) in its usable life cycle

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75
Q

What is optical storage?

A

A type of storage that uses laser light to read and write data, and includes CDs, DVDs and Blu-ray discs

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76
Q

What is dual layering?

A

Using two recording layers in storage media such as DVDs and some Blu-rays

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77
Q

What is virtual memory?

A

A memory management system that makes use of secondary storage and software to enable a computer to compensate for the shortage of actual physical RAM memory

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78
Q

What is disk thrashing (HDD)?

A

A problem in a hard disk drive (HDD) caused by excessive swapping in and out of data causing a high rate of head movements during virtual memory operations

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79
Q

What is the thrash point?

A

The point at which the execution of a program comes to a halt because the system is so busy moving data in and out of memory rather than actually executing the program

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80
Q

What is data redundancy?

A

The unnecessary storing of the same data on several storage devices at the same time

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81
Q

What is cloud storage?

A

A method of data storage where data is stored on offsite servers; the physical storage may be on hundreds of servers in many locations

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82
Q

What is network interface card (NIC)?

A

A hardware component (circuit board or chip) that is required to allow a device to connect to a network, such as the internet

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83
Q

What is a router?

A

A device that enables data packets to be moved between networks, for example, to join a LAN to a WAN

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84
Q

What is a static IP address?

A

An IP address that doesn’t change

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85
Q

What is a MAC address?

A

A unique identifier which acts as a network address for a device; it takes the form NN - NN - NN - DD - DD - DD, where NN is the manufacturer code and DD is the device code

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86
Q

What is a dynamic IP address?

A

A temporary IP address assigned to a device each time it logs onto a network

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87
Q

What is dynamic host configuration protocol (DHCP)?

A

A server that automatically provides and assigns an IP address

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88
Q

What does a CPU consist of?

A
  • control unit (CU)
  • arithmetic and logic unit (ALU)
  • registers and buses
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89
Q

What are the main novel features of von Neumann architecture?

A
  • the concept of a central processing unit (CPU or processor)
  • the CPU was able to access the memory directly
  • computer memories could store programs as well as data
  • stored programs were made up of instructions which could be executed in sequential order
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90
Q

Arithmetic & Logic Unit (ALU)

A

The Arithmetic & Logic Unit (ALU) allows the required arithmetic (e.g. +, - and shifting), or logic (e.g. AND, OR) operations to be carried out while a program is being run; it is possible for a computer to have more than one ALU to carry out specific functions. Multiplication and division are carried out by a sequence of addition, subtraction and left or right logical shift operations

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91
Q

Control Unit (CU)

A

The control unit reads an instruction from memory. The address of the location where the instruction can be found is stored in the Program Counter (PC). This instruction is then interpreted using the Fetch-Decode-Execute cycle. During that process, signals are generated along the control bus to tell other components in the computer what to do. The control unit ensures synchronisation of data flow and program instructions throughout the compute. A system clock is used to produce timing signals on the control bus to ensure this vital synchronisation takes place - without the clock the computer would simply crash.

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92
Q

Purpose of the current instruction register (CIR)

A

this register stores the current instruction being decoded and executed

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93
Q

Purpose of the accumulator (ACC)

A

This register is used when carrying out ALU calculations; it stores data temporarily during the calculations

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94
Q

Purpose of the memory address register (MAR)

A

This register stores the address of the memory location currently being read from or written to

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95
Q

Purpose of memory data/ buffer register (MDR)

A

This register stores data which has just been read from memory or data which is about to be written to memory

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96
Q

Purpose of program counter (PC)

A

This register stores the address where the next instruction to be read can be found

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97
Q

(System) buses

A

(System) buses are used in computers as parallel transmission components; each wire in the bus transmits one bit of data. There are three common buses used in the von Neumann architecture known as: address bus, data bus and control bus

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98
Q

Address bus

A

The address bus carries addresses throughout the computer system. Between the CPU and memory, the address bus is unidirectional (i.e. bits can travel in one direction only); this prevents addresses being carried back to the CPU, which would be an undesirable feature.
The width of a bus is very important. The wider the bus, the more memory locations that can be directly addressed at any given time, e.g. a bus of width 16 bits can address 65 535 (2 to the 16) memory locations whereas a bus width of 32 bits allows 4 294 967 296 memory locations to be simultaneously addressed. However, even this isn’t large enough for modern computers but the technology behind even wider buses is outside the scope of this book

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99
Q

Data bus

A

The data bus is bidirectional (allowing data to be sent in both directions along the bus). This means data can be carried from CPU to memory (and vice versa) and to and from input/output devices. It is important to point out that data can be an address, an instruction or a numerical value. As with the address bus, the width of the data bus is important; the wider the bus the larger the word length that can be transported. (A word is a group of bits which can be regarded as a single unit e.g. 16-bit, 32-bit or 64-bit word lengths are the most common.) Larger word lengths can improve the computer’s overall performance

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100
Q

Control bus

A

The control bus is also bidirectional. It carries signals from the control unit (CU) to all the other computer components. It is usually 8-bits wide. There is no real need for it to be any wider since it only carries control signals

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101
Q

Fetch-Decode-Execute cycle: Fetch

A

Both data and instruction can be stored in MDR. In the Fetch-Decode-Execute cycle, the next instruction is fetched from the memory address currently stored in the MAR and the instruction is stored in the MDR. The contents of the MDR are then copied to the Current Instruction Register (CIR). The PC is then incremented (increased by 1) so that the next instruction can then be processed

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102
Q

Fetch-Decode-Execute cycle: Decode

A

The instruction is then decoded so that it can be interpreted in the next part of the cycle

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103
Q

Fetch-Decode-Execute cycle: Execute

A

The CPU passes the decoded instruction as a set of control signals to the appropriate components within the computer system. This allows each instruction to be carried out in its logical sequence.

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104
Q

What factors (apart from clock speed) affect a computer’s overall performance?

A
  1. The width of the address bus and data bus can also affect computer performance and needs to be taken into account
  2. Overclocking. The clock speed can be changed by accessing the BIOS and altering the settings. However, using a clock speed higher than the computer was designed for can lead to problems, e.g.:
    i. Execution of instructions outside design limits can lead to seriously unsynchronised operations (i.e. an instruction is unable to complete in time before the next one is due to be executed) - the computer would frequently crash and become unstable
    ii. overclocking can lead to serious overheating of the CPU again leading to unreliable performance
  3. The use of cache memories can also improve CPU performance. Unlike RAM, cache memory is located within the CPU itself, which means it has much faster data access times than RAM. Cache memory stores frequently used instructions and data that need to be accessed faster, which improves CPU performance. When a CPU wishes to read memory, it will first check out the cache and then move on to main memory/RAM if the required data isn’t there. The larger the cache memory size the better the CPU performance
  4. The use of a different number of cores can improve computer performance
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105
Q

How does the number of cores change computer performance?

A

Doubling the number of cores doesn’t necessarily double the computer’s performance since we have to take into account the need for the CPU to communicate with each core; this will reduce overall performance.
E.g. with a dual core the CPU communicates with both cores using one channel reducing some of the potential increase in its performance, while with a quad core the CPU communicates with all four cores using six channels, considerably reducing potential performance.

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106
Q

How do different factors affect computer performance?

A
  • increasing bus width (data and address buses) increases the performance and speed of a computer system
  • increasing clock speed will potentially increase the speed of a computer
  • a computer’s performance can be changed by altering bus width, clock speed and use of multi-core CPUs
  • use of cache memories can also speed up a CPU’s performance
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107
Q

What can embedded systems be based on?

A
  • microcontrollers
  • microprocessor
  • system on chips (SoC)
108
Q

Embedded systems based on microcontrollers

A

This has a CPU in addition to some RAM and ROM and other peripherals all embedded onto one single chip (together they carry out a specific task)

109
Q

Embedded systems based on microprocessor

A

integrated circuit which only has a CPU on the chip (there is no RAM, ROM or peripherals - these need to be added)

110
Q

Embedded systems based on system on chips (SoC)

A

This may contain a microcontroller as one of its components (they almost always will include CPU, memory, input/output (I/O) ports and secondary storage on a single microchip)

111
Q

How do programmable devices permit upgrading?

A
  • connecting the device to a computer and allowing the download of updates to the software (for example, this is used to update the maps on a GPS system used in a vehicle)
  • automatic updates via a Wi-Fi, satellite or cellular (mobile phone network) link (for example, many modern cars allow updates to engine management systems and other components via satellite link)
112
Q

Benefits of devices being controlled using embedded systems

A
  • they are small in size and therefore easy to fit into devices
  • compared to other systems, they are relatively low cost to make
  • they are usually dedicated to one task allowing simple interfaces and often no requirement for an operating system
  • they consume very little power
  • they can be controlled remotely using a mobile phone, for example
  • very fast reaction to changing input (operate in real time and are feedback orientated)
  • with mass production comes reliability
113
Q

Drawbacks of devices being controlled using embedded systems

A
  • it can be difficult to upgrade some devices to take advantage of new technology
  • troubleshooting faults in the device becomes a specialist task
  • although the interface can appear to be more simple (e.g. a single knob) in reality it can be more confusing (e.g. changing the time on a cooker clock can require several steps)
  • any device that can be accessed over the internet is also open to hackers, viruses, etc.
  • due to the difficulty in upgrading and fault finding, devices are often just thrown away rather than being repaired (very wasteful)
  • can lead to an increase in the ‘throw away’ society if devices are discarded just because they have become out-of-date
114
Q

True or False: embedded systems cannot be controlled remotely

A

False

115
Q

What happens when a barcode is scanned?

A
  • the barcode is first of all read by a red laser or red LED (light emitting diode)
  • light is reflected back off the barcode; the dark areas reflect little or no light, which allows the bars to be read
  • the reflected light is read by sensors (photoelectric cells)
  • as the laser or LED light is scanned across the barcode, a pattern is generated, which is converted into digital data- this allows the computer to understand the barcode
116
Q

How is a keypad used in supermarkets?

A

to key in the number of same items bought; to key in a weight, to key in the number under the barcode if it cannot be read by the barcode reader/scanner

117
Q

How is a screen/monitor used in supermarkets?

A

To show the cost of an item and other information

118
Q

How is a speaker used in supermarkets?

A

To make a beeping sound every time a barcode is read correctly; but also to make another sound if there is an error when reading the barcode

119
Q

How is a printer used in supermarkets?

A

To print out a receipt/itemised list

120
Q

How is a card reader/chip and PIN used in supermarkets?

A

To read the customer’s credit/debit card (either using PIN or contactless)

121
Q

How is touchscreen used in supermarkets?

A

To select items by touching an icon (such as fresh fruit which may be sold loose without packaging)

122
Q

What happens when a barcode has been read?

A
  • the barcode number is looked up in the stock database (the barcode is known as the key field in the stock item record); this key field uniquely identifies each stock item
  • when the barcode number is found, the stock item record is looked up
  • the price and other stock item details are sent back to the checkout (or point of sale terminal (POS))
  • the number of stock items in the record is reduced by 1 each time the barcode is read
  • this new value for number of stock is written back to the stock item record
  • this number of stock items is compared to the re-order level; if it is less than or equal to this value, more stock items are automatically ordered
  • once an order for more stock items is generated, a flag is added to the record to stop re-ordering every time the stock item barcode is read
  • when new stock items arrive, the stock levels are updated in the database
123
Q

Advantages to the management of using barcodes

A
  • much easier and faster to change prices on stock items
  • much better, more up-to-date sales information/sales trends
  • no need to price every stock item on the shelves (this reduces time and cost to the management)
  • allows for automatic stock control
  • possible to check customer buying habits more easily by linking barcodes to, for example, customer loyalty cards
124
Q

Advantages to the customers of using barcodes

A
  • faster checkout queues (staff don’t need to remember/ look up prices of items)
  • errors in charging customers is reduced
  • the customer is given an itemised bill
  • cost savings can be passed on to the customer
  • better track of ‘sell by dates’ so food should be fresher
125
Q

Description of QR codes

A
  • A QR code consists of a block of small squares (light and dark) known as pixels. It can presently hold up to 4296 characters (or up to 7089 digits) and also allows internet addresses to be encoded within the QR code. This compares to the 30 digits that is the maximum for a barcode. However, as more and more data is added, the structure of the QR code becomes more complex.
  • The three large squares at the corners of the code function as a form of alignment; the remaining small corner square is used to ensure the correct size and correct angle of the camera shot when the QR code is read
126
Q

Uses of QR codes

A
  • advertising products
  • giving automatic access to a website or contact telephone number
  • storing boarding passes electronically at airports and train stations
127
Q

Advantages of QR codes compared to traditional barcodes

A
  • They can hold much more information
  • There will be fewer errors; the higher capacity of the QR code allows the use of built-in error-checking systems - normal barcodes contain almost no data redundancy (data which is duplicated) therefore it isn’t possible to guard against badly printed or damaged barcodes
  • QR codes are easier to read; they don’t need expensive laser or LED (light emitting diode) scanners like barcode - they can be read by the cameras on smartphones or tablets
  • It is easy to transmit QR codes either as text messages or images
  • It is also possible to encrypt QR codes which gives them greater protection than traditional barcodes
128
Q

Disadvantages of QR codes compared to traditional barcodes

A
  • More than one QR format is available
  • QR codes can be used to transmit malicious codes - known as attagging. Since there are a large number of free apps available to a user for generating QR codes, that means anyone can do this. It is relatively easy to write malicious code and embed this within the QR code. When the code is scanned, it is possible the creator of the malicious code could gain access to everything on the user’s phone (e.g. photographs, address book, stored passwords, and so on). The user could also be sent to a fake website where it is even possible for a virus to be downloaded
129
Q

What tasks does the embedded system controlling a digital camera automatically do?

A
  • adjust the shutter speed
  • focus the image automatically
  • operate the flash gun automatically
  • adjust the aperture size
  • adjust the size of the image
  • remove ‘red eye’ when the flash gun has been used
  • etc.
130
Q

What happens a photograph is taken on a digital camera?

A
  • The image is captured when light passes through the lens onto a light-sensitive cell; this cell is made up of millions of tiny sensors which are acting as photodiodes (i.e. charge couple devices (CCD) which convert light into electricity)
  • each of the sensors are often referred to as pixels (picture elements) since they are tiny components that make up the image
  • the image is converted into tiny electric charges which are then passed through an analogue to digital converter (ADC) to form a digital image array
  • the ADC converts the electric charges from each pixel into levels of brightness (now in a digital format); for example, an 8-bit ADC gives 2^8 (256) possible brightness levels per pixel
  • apart from brightness, the sensors also measure colour which produces another binary pattern; most cameras use a 24-bit RGB system (each pixel has 8 bits representing each of the 3 primary colours), which means each pixel has a red value (0 to 255 in denary), a green value (0 to 255) and a blue value (0 to 255)
  • the number of pixels determines the size of the file used to store the photograph
  • the quality of the image depends on the recording device (how good the camera lens is and how good the sensor array is), the number of pixels used (the more pixels used, the better the image), the levels of light and how the image is stored (JPEG, raw file, and so on)
131
Q

How does the computer recognise a letter pressed on the keyboard?

A
  • There is a membrane or circuit board at the base of the keys
  • The CPU in the computer can then determine which key has been pressed
  • The CPU refers to an index file to identify which character the key press represents
  • Each character on a keyboard has a corresponding ASCII value
132
Q

How do microphones work?

A
  • When sound is created, it causes the air to vibrate
  • When a diaphragm in the microphone picks up the air vibrations, the diaphragm also begins to vibrate
  • A copper coil is wrapped around the cone which is connected to the diaphragm. As the diaphragm vibrates, the cone moves in and out causing the copper coil to move backwards and forwards
  • This forwards and backwards motion causes the coil to cut through the magnetic field around the permanent magnet, inducing an electric current
  • The electric current is then either amplified or sent to a recording device. The electric current is analogue in nature
133
Q

Benefits of an optical mouse over a mechanical mouse

A
  • There are no moving parts, therefore it is more reliable
  • Dirt can’t get trapped in any of the mechanical components
  • There is no need to have any special surfaces
134
Q

Advantages of a wired mouse

A
  • No signal loss since there is a constant signal pathway (wire)
  • cheaper to operate (no need to buy new batteries or charge batteries)
  • fewer environmental issues (no need to dispose of old batteries)
135
Q

What are the different types of capacitive touch screens?

A
  • surface
  • projective
136
Q

Projective capacitive screen advantages compared to infrared and resistive

A
  • Better image clarity than resistive screens, especially in strong sunlight
  • Very durable screens that have high scratch resistance
  • Projective capacitive screens allow multi-touch
137
Q

Projective capacitive screen disadvantages compared to infrared and resistive

A
  • Surface capacitive screens only work with bare fingers or a special stylus
  • They are sensitive to electromagnetic radiation (such as magnetic fields or microwaves)
138
Q

What are the three types of touch screen technologies?

A
  • capacitive
  • infrared
  • resistive (currently most common)
139
Q

Advantages of infrared touch screens compared to capacitive and resistive

A
  • Allows multi-touch facilities
  • Has good screen durability
  • The operability isn’t affected by a scratched or cracked screen
140
Q

Disadvantages of infrared touch screens compared to capacitive and resistive

A
  • The screen can be sensitive to water or moisture
  • It is possible for accidental activation to take place if the infrared beams are disturbed in some way
  • Sometimes sensitive to light interference
141
Q

Advantages of resistive touch screens compared to the other two technologies

A
  • Good resistance to dust and water
  • Can be used with bare fingers, stylus and gloved hand
142
Q

Disadvantages of resistive touch screens compared to the other two technologies

A
  • Low touch sensitivity (sometimes have to press down harder)
  • Doesn’t support multi-touch facility
  • Poor visibility in strong sunlight
  • Vulnerable to scratches on the screen (made of polymer)
143
Q

What are the two types of light projectors?

A
  • digital light projector (DLP)
  • liquid crystal display (LCD) projector
144
Q

How do Digital light projectors (DLP) work?

A

The number of micro mirrors and the way they are arranged on the DMD chip determines the resolution of the digital image. When the micro mirrors tilt 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. The micro mirrors can switch on or off several thousand times a second creating various grey shades- typically 1024 grey shades can be produced (e.g. if the mirror switches on more often than it switches off, it will produce a lighter shade of grey)- known as a greyscale image.

A bright white light source (e.g. from a xenon bulb) passes through a colour filter on its way to the DMD chip. The white light is split into the primary colours: red, green and blue - the DLP projector can create over 16 million different colours. The ON and OFF states of each micro mirror are linked with colours from the filter to produce the coloured image

145
Q

How do liquid crystal display (LCD) projectors work?

A
  • A powerful beam of white light is generated from a bulb or LED inside the projector body
  • this beam of light is then sent to a group of chromatic-coated mirrors (known as dichromic mirrors); these reflect the light back at different wavelengths
  • when the white light hits these mirrors, the reflected light has wavelengths corresponding to red, green and blue light components
  • these three different coloured light components pass through three LCD screens (each screen is composed of thousands of tiny pixels which can either block light or let it through; this produces a monochromatic image)
  • consequently, three different versions of the same image are now produced - one is the whole image in different shades of red, one is the whole image in different shades of green and one is the whole image in different shades of blue
  • these images are then re-combined using a special prism to produce a full colour image
  • finally, the image passes through the projector lens onto a screen
146
Q

Advantages of digital light projector (DLP)

A
  • higher contrast ratios
  • higher reliability/longevity
  • quieter running than LCD projector
  • uses a single DMD chip, which mean no issues lining up the images
  • smaller and lighter than LCD projector
  • they are better suited to dusty or smoky atmospheres than LCD projectors
147
Q

Advantages of LCD projector

A
  • give a sharper image than DLP projectors
  • have better colour saturation than DLP projectors
  • more efficient in their use of energy than DLP technology - consequently they generate less heat
148
Q

Disadvantages of digital light projectors

A
  • image tends to suffer from ‘shadows’ when showing a moving image
  • DLP do not have grey components in the image
  • the colour definition is frequently not as good as LCD projectors because the colour saturation is not as good (colour saturation is the intensity of a colour)
149
Q

Disadvantages of LCD projectors

A
  • although improving, the contrast ratios are not as good as DLPs
  • LCD projectors have a limited life (that is, the longevity is not as good as DLPs)
  • since LCD panels are organic in nature, they tend to degrade with time (screen turn yellow and the colours are subsequently degraded over time)
150
Q

What is an inkjet printer made up of?

A
  • a print head, which consists of nozzles that spray droplets of ink onto the paper to form characters
  • an ink cartridge or cartridges; either one cartridge for each colour (blue, yellow and magenta) and a black cartridge or one single cartridge containing all three colours + black (NB: some systems use six colours)
  • a stepper motor and belt, which moves the print head assembly across the page from side to side
  • a paper feed, which automatically feeds the printer with pages as they are required
151
Q

Inkjet printing process: stage 1

A

the data from the document is sent to a printer driver

152
Q

Inkjet printing process: stage 2

A

the printer driver ensures that the data is in a format that the chosen printer can understand

153
Q

Inkjet printing process: stage 3

A

a check is made by the printer driver to ensure that the chosen printer is available to print (e.g. is it busy, is it off-line, is it out of ink, and so on)

154
Q

Inkjet printing process: stage 4

A

the data is then sent to the printer and it is stored in a temporary memory known as a printer buffer

155
Q

Inkjet printing process: stage 5

A

a sheet of paper is then fed into the main body of the printer; a sensor detects whether paper is available in the paper feed tray - if it is out of paper (or the paper is jammed) then an error message is sent back to the computer

156
Q

Inkjet printing process: stage 6

A

as the sheet of paper is fed through the printer, the print head moves from side to side across the paper printing the text or image; the four ink colours are sprayed in their exact amounts to produce the desired final colour

157
Q

Inkjet printing process: stage 7

A

at the end of each full pass of the print head, the paper is advanced very slightly to allow the next line to be printed; this continues until the whole page has been printed

158
Q

Inkjet printing process: stage 8

A

if there is more data in the printer buffer, then the whole process from stage 5 is repeated until the buffer is finally empty

159
Q

Inkjet printing process: stage 9

A

once the printer buffer is empty, the printer sends an interrupt to the CPU in the computer; this is a request for more data to be sent to the printer; the whole process continues until the whole of the document has been printed

160
Q

Laser printing process: stage 1

A

the data from the document is sent to a printer driver

161
Q

Laser printing process: stage 2

A

the printer driver ensures that the data is in a format that the chosen printer can understand

162
Q

Laser printing process: stage 3

A

a check is made by the printer driver to ensure that the chosen printer is available to print (e.g. is it busy, is it off-line, is it out of ink, and so on)

163
Q

Laser printing process: stage 4

A

the data is then sent to the printer and it is stored in a temporary memory known as a printer buffer

164
Q

Laser printing process: stage 5

A

the start of the printing process involves a printing drum being given a positive charge; as this drum rotates, a laser beam is scanned across it removing the positive hare in certain areas; this leaves negatively charged areas that exactly match the text/images of the page to be printed

165
Q

Laser printing process: stage 6

A

the drum is then coated with positively charged toner (powdered ink); since the toner is positively charged, it only sticks to the negatively charged parts of the drum

166
Q

Laser printing process: stage 7

A

a negatively charged sheet of paper is then rolled over the drum

167
Q

Laser printing process: stage 8

A

the toner on the drum now sticks to the paper to produce an exact copy of the page sent to the printer

168
Q

Laser printing process: stage 9

A

to prevent the paper sticking to the drum, the electric charge on the paper is removed after one rotation of the drum

169
Q

Laser printing process: stage 10

A

the paper finally goes through a fuser which is a set of heated rollers; the heat melts the ink so that it fixes permanently to the paper

170
Q

Laser printing process: stage 11

A

at the very end, a discharge lamp removes all the electric charge from the drum making it ready to print the next page

171
Q

Applications of inkjet printers

A

Inkjet printers are often used for printing one-off photos or where only a few pages of good quality, colour printing is needed; the small ink cartridges or small paper trays would not be an issue with such applications

172
Q

Applications of laser printers

A

These devices produce high quality printouts and are very fast when making multiple copies of a document; any application that needs high volume printing (in colour or monochrome) would choose the laser printer (e.g. producing a large number of of high-quality flyers or posters for advertising). Laser printers have two advantages: they have large toner cartridges and large paper trays (often holding more than a ream of paper)

173
Q

What are some features of 3D printing?

A
  • Various types of 3D printers exist; they range from the size of a microwave oven up to the size of a small car
  • 3D printers use additive manufacturing (i.e. the object is built up layer by layer); this is in sharp contrast to the more traditional method of subtractive manufacturing (i.e. removal of material to make the object)
  • Direct 3D printing uses inkjet technology; a print head can move left to right as in a normal printer. However, the print head can also move up and down to build up the layers of an object
  • Binder 3D printing is similar to direct 3D printing. However, this method uses two passes for each of the layers; the first pass sprays dry powder and then on the second pass a binder (a type of glue) is sprayed to form a solid layer
  • Newer technologies are using laser and UV light to harden liquid polymers; this further increases the diversity of products which can be made
174
Q

Process of producing an object using a 3D printer

A
  1. A design is made using computer aided design (CAD) software
  2. The finalised drawing is imported into some special software that prepares it in a format that is understood by the 3D printer
  3. The 3D printer is first set up to allow the solid object to be made
  4. The solid object is built up layer by layer (often only 0.1 mm thick); this can take several hours depending on the thickness of the layers, the material used and the size of the final object
  5. The object is removed from the printer and is then prepared; e.g. some use a jelly-like support that needs to be washed away by immersion in water, some require the removal of excess plastic powder and others require the cutting away of unused material; in many cases, the object has to be left to ‘cure’ for a few hours
175
Q

Uses of 3D printing

A
  • the covering of prosthetic limbs can be made to exactly fit the limb
  • making items to allow precision reconstructive surgery (e.g. facial reconstruction following an accident); the parts made by this technique are more precise in their design since they can be made from exact scanning of the skull
  • in aerospace, manufacturers are looking at making wings and other parts using 3D technology; the bonus will be lightweight precision parts
  • fashion and art - 3D printing allows new creative ideas to be developed
  • making parts for items no longer in production e.g. suspension parts for a vintage car
176
Q

Advantages of LED back lighting over CCFL technology

A
  • LEDs reach their maximum brightness almost immediately (there is no need to ‘warm up’ before reaching full efficiency)
  • LEDs give a whiter light that sharpens the image and makes the colours appear more vivid; CCFL had a slightly yellowish tint
  • LEDs produce a brighter light that improves the colour definition
  • monitors using LED technology are much thinner than monitors using CCFL technology
  • LEDs last indefinitely; this makes the technology more reliable and makes for a more consistent product
  • LEDs consume very little power which means they produce less heat as well as using less energy
177
Q

Advantages of using OLED compared to existing LEDs and LCDs

A
  • The plastic, organic layers of an OLED are thinner, lighter and more flexible than the crystal structures used in LEDs or LCDs
  • The light-emitting layers of an OLED are lighter; OLED layers can be made from plastic rather than the glass as used in LED and LCD screens
  • OLEDs give a brighter light than LEDs
  • OLEDs do not require backlighting like LCD screens- OLEDs generate their own light
  • Since OLEDs require no backlighting, they use much less power than LCD screens (most of the LCD power is used to do the backlighting); this is very important in battery-operated devices such as mobile phones
  • Since OLEDs are essentially plastics, they can be made into large, thin sheets (this means they could be used on large advertising boards in airports, subways and so on)
  • OLEDs have a very large field of view, about 170 degrees, which makes them ideal for use in television sets and for advertising screens
178
Q

How does digitised sound stored on a file become converted into sound?

A
  • The digital data is first passed through a digital to analogue converter (DAC) where it is changed into an electric current
  • This is then passed through an amplifier (since the current generated by the DAC will be very small); this creates a current large enough to drive a loudspeaker
  • This electric current is then fed to a loudspeaker where it is converted into sound
179
Q

How does a loudspeaker convert electric current into sound?

A
  • When an electric current flows through the coil of wire that is wrapped around an iron core, the core becomes a temporary electromagnet; a permanent magnet is also positioned very close to this electromagnet
  • As the electric current through the coil of wire varies, the induced magnetic field in the iron core also varies. This causes the iron core to be attracted towards the permanent magnet and as the current varies this will cause the iron core to vibrate
  • Since the iron core is attached to a cone (made of paper or thin synthetic material), this causes the cone to vibrate, producing sound waves
180
Q

What does a temperature sensor do?

A

measures temperature of the surroundings by sending signals; these signals will change as the temperature changes

181
Q

What does a moisture sensor do?

A

measures water levels in, for example, soil (it is based on the electrical resistance of the sample being monitored)

182
Q

What does a humidity sensor do?

A

slightly different to moisture- measures the amount of water vapour in, for example, a sample of air (based on the fact that the conductivity of air will change depending on the amount of water present)

183
Q

What does a light sensor do?

A

these use photoelectric cells that produce an output (in the form of an electric current) depending on the brightness of the light

184
Q

What does an active infrared sensor do?

A

these use an invisible beam of infrared radiation picked up by a detector; if the beam is broken, then there will be a change in the amount of infrared radiation reaching the detector (sensor)

185
Q

What does a passive infrared sensor do?

A

these sensors measure the heat radiation given off by an object, for example, the temperature of an intruder or the temperature in a fridge

186
Q

What does a pressure sensor do?

A

a pressure sensor is a transducer and generates different electric currents depending on the pressure applied

187
Q

What does an acoustic/sound sensor do?

A

these are basically microphones that convert detected sound into electric signals/pulses

188
Q

What does a gas sensor do?

A

most common ones are oxygen or carbon dioxide sensors; they use various methods to detect the gas being monitored and produce outputs that vary with the oxygen or carbon dioxide levels present

189
Q

What does a pH sensor do?

A

these measure acidity through changes in voltages in, for example, soil

190
Q

What does a magnetic field sensor do?

A

these sensors measure changes in magnetic fields- the signal output will depend on how the magnetic field changes

191
Q

What does an accelerometer sensor do?

A

these are sensors that measure acceleration and motion of an application, i.e. the change in velocity (a piezoelectric cell is used whose output varies according to the change in velocity)

192
Q

What does a proximity sensor do?

A

these sensors detect the presence of a nearby object

193
Q

What does a flow (rate) sensor do?

A

these sensors measure the flow rate of a moving liquid or gas and produce an output based on the amount of liquid or gas passing over the sensor

194
Q

What does a level sensor do?

A

these sensors use ultrasonics (to detect changing liquid levels in, for example, a tank) or capacitance/conductivity (to measure static levels (for example, height of water in a river))- note, level sensors can also be optical or mechanical in nature

195
Q

Example applications of temperature sensor

A
  • control of a central heating system
  • control/monitor a chemical process
  • control/monitor temperature in a greenhouse
196
Q

Example applications of moisture sensor

A
  • control/monitor moisture levels in soil in a greenhouse
  • monitor the moisture levels in a food processing factory
197
Q

Example applications of humidity sensor

A
  • monitor humidity levels in a building
  • monitor humidity levels in a factory manufacturing microchips
  • monitor/control humidity levels in the air in a greenhouse
198
Q

Example applications of light sensor

A
  • switching street lights on or off depending on light levels
  • switch on car headlights automatically when it gets dark
199
Q

Example applications of active infrared sensor

A
  • turn on car windscreen wipers automatically when it detects rain on the windscreen
  • security alarm system (intruder breaks the infrared beam)
200
Q

Example applications of passive infrared sensor

A
  • security alarm system (detects body heat)
  • monitor the temperature inside an industrial freezer or chiller unit
201
Q

Example applications of pressure sensor

A
  • weighing of lorries at a weighing station
  • measure the gas pressure in a nuclear reactor
202
Q

Example applications of acoustic/sound sensor

A
  • pick up the noise of footsteps in a security system
  • detect the sound of liquids dripping at a faulty pipe joint
203
Q

Example applications of gas sensor

A
  • monitor pollution levels in the air at an airport
  • monitor oxygen and carbon dioxide levels in a greenhouse
  • monitor oxygen levels in a car exhaust
204
Q

Example applications of pH sensor

A
  • monitor/control acidity levels in the soil in a greenhouse
  • control acidity levels in a chemical process
205
Q

Example applications of magnetic field sensor

A
  • detect magnetic field changes (for example, in mobile phones and CD players)
  • used in anti-lock braking systems in cars
206
Q

Example applications of accelerometer sensor

A
  • used in cars to measure rapid deceleration and apply air bags in a crash
  • used by mobile phones to change between portrait and landscape mode
207
Q

Example applications of proximity sensor

A
  • detect when a face is close to a mobile phone screen and switches off screen when held to the ear
208
Q

Example applications of flow (rate) sensor

A
  • used in respiratory devices and inhalers in hospitals
  • measure gas flows in pipes (for example, natural gas)
209
Q

Example applications of level sensor

A
  • monitor levels in a petrol tank in a car
  • inn a pharmaceutical process where powder levels in tablet production need to be monitored
  • leak detection in refrigerant (air conditioning)
210
Q

Examples of monitoring

A
  • Monitoring of a patient in a hospital for vital signs such as heart rate, temperature, etc.
  • Monitoring of intruders in a burglar alarm system
  • Checking the temperature levels in a car engine
  • Monitoring pollution levels in a river
211
Q

Examples of control

A
  • Turning street lights on at night and turning them off again during daylight
  • controlling the temperature in a central heating/air conditioning system
  • chemical process control (for example, maintaining temperature and pH of process)
212
Q

What actions will a security monitoring system carry out?

A
  • the system is activated by keying in a password on a keypad
  • the infrared sensor will pick up the movement of an intruder in the building
  • the acoustic sensor will pick up sounds such as footsteps or breaking glass
  • the pressure sensor will pick up the weight of an intruder coming through a door or through a window
  • the sensor data is passed through an ADC if it is in an analogue form to produce digital data
  • the computer/microprocessor will sample the digital data coming from these sensors at a given frequency (e.g. every 5 seconds)
  • the data is compared with the stored values by the computer/microprocessor
  • if any of the incoming data values are outside the acceptable range, then the computer sends a signal to a siren to sound the alarm, or to a light to start flashing
  • a DAC is used if the devices need analogue values to operate them
  • the alarm continues to sound/lights continue to flash until the system is reset with a password
213
Q

How are patients monitored in a hospital using monitoring applications?

A
  • A number of sensors are attached to the patient, measuring vital signs such as temp, heart rate, breathing rate, etc.
  • these sensors are all attached to a computer system
  • the sensors constantly send data back to the computer system
  • the computer samples the data at frequent intervals
  • the range of acceptable values for each parameter is keyed into the computer
  • the computer compares the values from the sensors with those values keyed in
  • if anything is out of the acceptable range, a signal is sent by the computer to sound an alarm
  • if data from the sensors is within range, the values are shown in either graphical form on a screen and/or a digital read out
  • monitoring continues until the sensors are disconnected from the patient
214
Q

How is a microprocessor used to control the operation of a street lamp?

A
  • the light sensor sends data to the ADC interface
  • this changes the data into digital form and sends it to the microprocessor
  • the microprocessor samples the data every minute (or at some other frequency rate)
  • if the data from the sensor < value stored in memory a signal is sent from the microprocessor to the street lamp
  • and the lamp is switched on
  • the lamp stays switched on for 30 mins before the sensor readings are sampled again (prevents the lamp flickering off and on during brief heavy cloud cover, for example)
  • if data from sensor >= value stored in memory, a signal is sent from the microprocessor to the street lamp
  • and lamp is switched off
  • lamp stays switched off for 30 mins before sensor readings are sampled again
215
Q

How does anti-lock braking systems on cars work?

A
  • when one of the car wheels rotates too slowly (i.e. it is locking up), a magnetic field sensor sends data to a microprocessor
  • the microprocessor checks the rotation speed of the other three wheels
  • if they are different (i.e. rotating faster), the microprocessor sends a signal to the braking system
  • and the braking pressure to the affected wheel is reduced
  • the wheel’s rotational speed is then increased to match the other wheels
  • the checking of the rotational speed using these magnetic field sensors is done several times a second
  • and the braking pressure to all the wheels can be constantly changing to prevent any of the wheel slocking up under heavy braking
  • this is felt as a ‘judder’ on the brake pedal as the braking system is constantly switched off and on to equalise the rotational speed of all four wheels
  • if one of the wheels is rotating too quickly, braking pressure is increased to that wheel until it matches the other three
216
Q

How do central heating systems work?

A
  • the required temperature is keyed in and this is stored in the microprocessor memory (called the pre-set value)
  • the temperature sensor is constantly sending data readings to the microprocessor
  • the sensor data is first sent to an ADC to convert the analogue data into digital data
  • the digital data is sent to the microprocessor
  • the microprocessor compares this data with the pre-set value
  • if the temperature reading >= pre-set value then no action is taken
  • if the temperature reading < pre-set value, then a signal is sent to an actuator (via a DAC) to open the gas valve to the heater to an actuator (via a DAC) to turn on the water pump
  • the process continues until the central heating is switched off
217
Q

How are sensors and computers used for chemical process control?

A
  • temperature and pH sensors read data from the chemical process
  • this data is converted to digital using an ADC and is then sent to the computer
  • the computer compares the incoming data with pre-set values stored in memory
  • if the temp < 70 C, a signal is sent to switch on the heater
  • if the temp >= 70C, a signal is sent to switch off the heaters
  • if the pH > 3.5, then a signal is sent to open a valve and acid is added
  • if the pH <= 3.5, then a signal is sent to close this valve
  • the computer signals will be changed into analogue signals using a DAC so that is can control the heaters and valves
  • this continues as long as the computer system is activated
218
Q

What different sensors could be used to control a greenhouse environment?

A
  • humidity
  • moisture
  • temperature
  • pH
  • light
219
Q

What are the two types of memory and storage devices?

A
  • primary memory
  • secondary storage
220
Q

What are the primary memories?

A
  • RAM
  • ROM
221
Q

What are the internal secondary storages?

A
  • Hard disk drive (HDD)
  • Solid state drive (SSD)
222
Q

What are the external secondary storages?

A
  • DVD/CD and DVD-RAM
  • Blu-ray disc
  • USB memory stick/flash memory
  • Removable hard drive
223
Q

Features of primary memory

A
  • Directly addressable by the CPU
  • Contains RAM, ROM and cache memory
224
Q

Features of secondary storage

A
  • Not directly addressable by the CPU
  • All are non-volatile devices
  • Can be external or internal to the computer
  • Examples include HDD, SSD, DVD, memory stick, Blu-ray disc
225
Q

Features of RAM

A
  • can be written to or read from, and the data can be changed by the user or the computer (i.e. a temporary memory)
  • used to store data, files, part of an application or part of the operating system currently in use
  • volatile- memory contents are lost when powering off the computer
  • can be increased in size to improve operational speed of a computer
226
Q

What are the types of RAM technology?

A
  • dynamic RAM (DRAM)
  • static RAM (SRAM)
227
Q

What is the function of a capacitor?

A

holds the bits of information (0 or 1)

228
Q

What is the function of a transistor

A

acts like a switch; it allows the chip control circuitry to read the capacitor or change the capacitor’s value

229
Q

Advantages of DRAMs over SRAMs

A
  • much less expensive to manufacture than SRAM
  • consume less power than SRAM
  • higher memory capacity than SRAM
230
Q

Features of DRAM

A
  • consists of a number of transistors and capacitors
  • needs to be constantly refreshed
  • less expensive to manufacture than SRAM
  • has a higher memory capacity than SRAM
  • main memory is constructed from DRAM
  • consumes less power than SRAM
231
Q

Features of SRAM

A
  • uses flip flops to hold each bit of memory
  • doesn’t need to be constantly refreshed
  • has a faster data access time than DRAM
  • CPU memory cache makes use of SRAM
232
Q

Features of ROM

A
  • non-volatile memory device
  • permanent memory device
  • data stored can only be read - can’t be altered
  • always used to store BIOS and other data needed at start up
233
Q

Functions of ROM

A
  • storing the factory settings such as remote control frequencies
  • storing the ‘start-up’ routines when the toy car is first switched on
  • storing of the set routines; for example, how the buttons on the hand-held device control turning left, acceleration, stopping, and so on
234
Q

Functions of RAM

A
  • the user may wish to program in their own routines; these new instructions would be stored in the RAM chip
  • the RAM chip will store the data/instructions received from the remote control unit
235
Q

What are the three categories of secondary (and off-line) storage?

A
  • magnetic
  • solid state
  • optical
236
Q

Benefits of floating gate and control gate transistor technology over hard disk drives

A
  • they are more reliable (no moving parts to go wrong)
  • they are considerably lighter (which makes them suitable for laptops)
  • they don’t have to ‘get up to speed’ before they work properly
  • they have a lower power consumption
  • they run much cooler than HDDs (both these points again make them very suitable for laptop computers)
  • because of no moving parts, they are very thin
  • data access is considerably faster than HDD
237
Q

What is the main drawback of SSD?

A

Longevity of technology (although this is becoming less of an issue)

238
Q

What are the main differences between DVD and Blu-ray?

A
  • a blue laser, rather than a red laser, is used to carry out read and write operations; the wavelength of blue light is only 405 nanometres (compared to 650 nm for red light)
  • using blue laser light means that the ‘pits’ and ‘lands’ can be much smaller; consequently, Blu-ray can store up to five times more data than normal DVD
  • single-layer Blu-ray discs can use a 1.2 nm thick polycarbonate disk; however, dual-layer Blu-ray and normal DVDs both use a sandwich of two 0.6 mm thick disks (i.e. 1.2 mm thick)
  • Blu-ray disks automatically come with a secure encryption system that helps to prevent piracy and copyright infringement
  • the data transfer rate for a DVD is 10Mbps and for a Blu-ray disc it is 36 Mbps (this equates to 1.5 hours to transfer 25GiB of data)
239
Q

Comparison of the capacity and interactivity of DVDs and Blu-ray discs

A
  • a standard dual-layer DVD has a storage capacity of 4.7 GB (enough to store a 2-hour standard definition movie)
  • a single-layer Blu-ray disc has a storage capacity of 27 GB (enough to store a 2-hour high definition movie or 13 hours of standard definition movies)
  • A dual-layer Blu-ray disc has a storage capacity of 50 GB (enough to store 4.5 hours of high definition movies or 20 hours of standard definition movies)
240
Q

Features of Blu-ray

A
  • record high definition television programs
  • skip quickly to any part of the disc
  • create playlists of recorded movies and television programmes
  • edit or re-order programmes recorded on the disc
  • automatically search for empty space on the disc to avoid over-recording
  • access websites and download subtitles and other interesting features
241
Q

Main benefits of virtual memory

A
  • programs can be larger than physical memory and still be executed
  • there is no need to waste memory with data that isn’t being used (e.g. during error handling)
  • it reduces the need to buy and install more expensive RAM memory (although as mentioned earlier there are limits to the value of doing this)
242
Q

What are the three common cloud storage systems?

A
  • public cloud
  • private cloud
  • hybrid cloud
243
Q

What is the public cloud?

A

a storage environment where the customer/client and cloud storage provider are different companie

244
Q

What is the private cloud?

A

storage provided by a dedicated environment behind a company firewall; customer/client and cloud storage provider are integrated and operate as a single entity

245
Q

What is the hybrid cloud?

A

a combination of the two above environments; some data resides in the private cloud and less sensitive/less commercial data can be accessed from a public cloud storage provider

246
Q

Benefits of using cloud storage

A
  • customer/client files stored on the cloud can be accessed at any time from any device anywhere in the world provided internet access is available
  • there is no need for a customer/client to carry an external storage device with them, or even use the same computer to store and retrieve information
  • the cloud provides the user with remote back-up of data with obvious benefits to alleviate data loss/disaster recovery
  • if a customer/client has a failure of their hard disk or back-up device, cloud storage will allow recovery of their data
  • the cloud system offers almost unlimited storage capacity
247
Q

Drawbacks of using cloud storage

A
  • if the customer/client has a slow or unstable internet connection, they would have many problems accessing or downloading their data/files
  • costs can be high if large storage capacity is required; it can also be expensive to pay for high download/upload data transfer limits with the customer/clients internet service provider (ISP)
  • the potential failure of the cloud storage company is always possible - this poses a risk of loss of all back-up data
248
Q

Why do MAC addresses need to be changed using LAA?

A
  • certain software used on mainframe systems need all the MAC addresses of devices to fall into a strict format; because of this, it may be necessary to change the MAC address of some devices to ensure they follow the correct format
  • it may be necessary to bypass a MAC address filter on a router or a firewall; only MAC addresses with a certain format are allowed through, otherwise the devices will be blocked if their MAC address doesn’t adhere to the correct format
  • to get past certain types of network restrictions it may be necessary to emulate unrestricted MAC addresses; hence it may require the MAC address to be changed on certain devices connected to the network
249
Q

Features of MAC addresses

A
  • identifies the physical address of a device on the network
  • unique for device on the network
  • assigned by the manufacturer of the device and is part of the NIC
  • they can be universal or local
  • when a packet of data is sent and received, the MAC address is used to identify the sender’s and recipient’s devices
  • use 48 bits
  • can be UAA or LAA
250
Q

Features of IP addresses

A
  • identifies the global address on the internet
  • may not necessarily be unique
  • dynamic IP addresses are assigned by ISP using DHCP each time the device connects to the internet
  • dynamic IP addresses change every time a device connects to the internet; static IP addresses don’t change
  • used in routing operations as they specifically identify where the device is connected to the internet
  • use either 32 bits (IPv4) or 128 bits (IPv6)
  • can be static or dynamic
251
Q

What are static IP addresses usually assigned to?

A
  • remote servers which are hosting a website
  • an online database
  • a File Transfer Protocol (FTP) server. FTP servers are used when files need to be transferred to various computers throughout the network
252
Q

Features of dynamic IP addresses

A
  • greater privacy since they change each time a user logs on
  • dynamic IP addresses can be an issue when using, for example, VoIP since this type of addressing is less reliable as it can disconnect and change the IP address causing the VoIP connection to fail
253
Q

Features of static IP addresses

A
  • since static IP addresses don’t change, they allow each device to be fully traceable
  • allow for faster upload and download speeds
  • more expensive to maintain since the device must be constantly running so that information is always available
254
Q

Accumulator (ACC)

A

Temporary general-purpose register that stores numerical values at any part of a given operation

255
Q

Address

A

A label for a memory location used by the CPU to track data

256
Q

Arithmetic and Logic Unit (ALU)

A

The component of the CPU that carries out all arithmetic and logical operations

257
Q

Backing store

A

A secondary storage device (such as HDD or SSD) used to store data permanently even when the computer is powered down

258
Q

Address bus

A

The system bus that carries the memory locations throughout the computer system

259
Q

ADC (analogue to digital converter)

A

A device that converts analogue data (e.g. read from sensors) into a form understood by a computer

260
Q

Function of the CPU

A

Executes step-by-step instruction using the fetch-decode-execute cycle

261
Q

What are examples of memory?

A

Registers, cache, RAM, virtual memory, etc.

262
Q

Function of storage

A

Stores program files and data even when not in use.

263
Q

What are examples of storage?

A

Hard drives, SD cards, USB memory disks, CDs, etc

264
Q

What does the speed of the computer depend on?

A

Speeds of the CPU, memory and bus speed

265
Q

How is the performance of a computer assessed?

A

Using a test called benchmarking

266
Q

What type of memory is cache?

A

Temporary

Computer science GCSE (12 decks)

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