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A Level Computer Science > GSCE Computer Science > Flashcards

GSCE Computer Science Flashcards

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1
Q

why do we need primary storage

A

RAM- store instructions while computer is running. CPU fetches instructions from RAM, stores operating system, currently in use programs, open applications and data in use
ROM- stores boot-up sequence for BIOS, loads operating system

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2
Q

difference between RAM and ROM

A 
ROM= non-volatile, usually fixed, contents of it hardly ever changes, smaller than RAM, stores boot up sequence, stores BIOS, loads operating system
RAM= volatile, easily expandable, contents change frequently, larger than ROM, stores programs currently in use, open applications, data in use and operating system
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3
Q

virtual memory

A

Part of secondary storage
Used to store data temporary’s when ram full, data moved from RAM to VM
Make space in RAM
So ram can be filled up with new data
Let’s you run applications larger than what ram can support
Let’s more memory be used than there is in the system
Allows us to open programs when RAM is full
When data in vm is needed, moved back to ram

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4
Q

Virtual memory disadvantage

A

slows down CPU performance - disk thrashing ( overuse of virtual memory)
Data has to go from virtual memory to ram to CPU and virtual memory is apart of solid state drive/hard disk/secondary storage
this transferring takes processor time

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5
Q

What is secondary storage

A

long term non-volatile storage of data/files
not constantly connected to computer and devices
isn’t directly accessible by CPU

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6
Q

Why is secondary storage needed

A

To permanently save files, data and programs when the computer is switched off
back up the data stored in ram
Need for larger storage capacity
RAM is volatile, ROM cannot be written to

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7
Q

what are the types of secondary storage

A

optical
magnetic
solid state

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8
Q

optical storage

A
  • slow
  • easily scratched - low reliability, low durability
  • small capacity 700mb -50gb
  • small
  • portability , easy to move about
  • cheap
  • no moving parts
  • can be backed up easily
  • can’t be over written, read-only
  • Can be read by other devices
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9
Q

magnetic storage

A

has moving parts so:

  • only reliable in a machine that doesn’t move
  • not portable though portable HDD can be get
  • has moving parts so not durable
  • slow-medium speed
  • very large capacity 1-12tb
  • cheap
  • Data could be corrupted if close enough to a magnetic field
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10
Q

Solid state storage

A 
No moving parts
Fast speed
Large capacity 250gb-2tb 
Portable
Durable
Reliable 
As no moving parts
Expensive cost
Can get lost
Wear out over a long time period
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11
Q

Properties you should consider when deciding on type of storage to use

A

capacity
cost
speed
size
portability- physical and if data can be moved from one device to another
durability- ability to resist damage, length of time expected for data to last
reliability- whether data will be saved as expected, data is not affected when saved, no changes to file formatting
robustness

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12
Q

How does optical storage work?

A

Laser light creates marks in a pattern on a disc

laser light detects where marks are and translates it into readable format

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13
Q

Optical storage capacity

A

CVD rom- up to 720mb
DVD- up to 8.4 gb
Blu ray- up to 50gb

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14
Q

How does magnetic storage work?

A

Info is written to/read from the storage medium as it spins by read-and-write heads that changes how magnetised that part of the medium is. heads that detect/ modify the magnetism to read data. magnetism is 1, demagnetised is 0

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15
Q

How do solid state storage work?

A

made of microchips (switches)

state of switches determine if 1 or 0 is stored

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16
Q

Optical storage examples
Magnetic storage examples
Solid state examples

A

Solid state storages- USBS drives, Solid state (SD) drives, memory cards, flash memory

Magnetic storage- magnetic tape, mechanical hard disk drives, portable HDD

Optical- Blu-ray, CVD-ROM, DVD

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17
Q

Units

A 
Bit (0 or 1)
Nibble (4 bits) 
Byte (8 bits)
Kilobyte (1,000 bytes or 1KB) 
Megabyte (1,000 KB)
Gigabyte (1,000 KB) 
Terabyte (1,000 GB) 
Petabyte (1,000 TB)
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18
Q

What is meant by a bit

A

the smallest representation of data, 1 or 0. Single binary digit

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19
Q

How data needs to be converted into a binary format to be processed by a computer

A

Computers consists of transistors/switches/logic circuits/ gates which only have two values/ on or off/1 or 0/ open or closed
Circuit only needs to check for two states/ uses switches electricity flowing or not flowing/on or off/1 and 0

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20
Q

Computers consist of

A

Binary numbers, 1 or 0
The circuit only needs to check for the states 1 or 0
Only understands binary

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21
Q

What is a overflow error

A

When we add or shift a number and it becomes too big for the register , number can’t fit into 8 bits and is greater than 11111111 and there is a extra carry/bit

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22
Q

Hexadecimal

A

One hexadecimal is equal to one nibble
made up of 4 bits per hex digit

used in: defining colours in graphics software, represent MAC addresses , displays address, for checksums

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23
Q

Advantages of hexadecimal

Why do people use hexadecimals to represent numbers stored in computers

A 
Straightforward to convert, easier to convert to binary as each hexadecimal digit is a nibble in binary
Shorter number to remember than binary 
Quicker to enter 
Less susceptible to errors
Easier to work with than binary
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24
Q

Binary shifts

A

Shift to right of binary, if u convert to denary you’ll see it has been divided by 2
Shift to left, multiply by 2

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25
Q

Character set

A

The range of characters (symbols, numbers, letters) that can be represented by a computer
each character has a binary value that computer understands/uses.

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26
Q

What is used to represent characters

A

Each character is assigned a unique character code (binary value)

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27
Q

Character set examples

A

ASCII: 7 bits, 128 characters
Extended ASCII: 8 bits, 256, more characters it can represent and European symbols and other languages
Unicode: 16 bits or up to 32 bits. Encodes set characters. All languages

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28
Q

What does ASCII stand for?

A

American Standard Code for Information Interchange
7 bit character system used to code the character set the computer uses
System uses code to represent characters, symbols, numbers

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29
Q

Why would Unicode be used

A

To use other special characters found in different languages

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30
Q

A image is made up of

A

pixels which have a binary value to them which represents a colour
Smallest element of a image
The binary numbers are stored in order in the file

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31
Q

Bitmap image

A

Based on pixels
Each have binary value
That represents a colour

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32
Q

Vector image

A

Based on mathematical algorithms

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33
Q

Colour depth

A

Amounts of bits stored per colour of pixel
How many colours that can be represented

The bigger the colour depth=The higher the accuracy, more colours can be represented.
But higher file size

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34
Q

Resolution

A

Number of pixels per inch of screen

For image: size of image. number of total pixels (image width x image height)

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35
Q

Increasing resolution

A

Only increases quality if screen is bigger
Smaller images on big screens, image is stretched and lowers quality
Otherwise, increasing resolution= decreases battery life
/larger file size as more pixels-more data needed to be stored

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36
Q

How does reducing the number of colours in a image can reduce its file size

A

Colour depth decrease
Fewer bits needed per colours
As less colours are represented
Which means fewer bits per pixel

Opposite: more colours, more bits required for each pixel
E.g
two bits per pixel (00 to 11) - four possible colours

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37
Q

Meta data

A

Background information (data) of a file
computer needs to know the size of the image (height, width, colour depth in bpp)
Allows the computer to recreate the image from binary

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38
Q

How sound is sampled and stored in digital form

A

Amplitude of waveform measured
Converted into binary
At regular intervals

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39
Q

Sample frequency

A

Number of samples taken per second

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40
Q

Bit rate

A

How much data is being processed per sec

Sample frequency x bit depth x channels

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41
Q

Bit depth (audio)

A

Number of bits taken per sample

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42
Q

Larger sample frequency and bit depth

A

Better quality
Higher file size
More bit depth- more sound/ data captured
More sample frequency- less time gap between each sample

Sound reproduced is closer to original- accuracy

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43
Q

The need for compression

A
  • Quicker upload/download/load/transfer time
  • Less storage space taken up
  • less mobile data/bandwidth usage
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44
Q

Lossless compression

A 
Uses algorithm to compress file
No data is lost (data lost is only temporary, comes back when file is uncompressed) 
Reduces file size less than lossy
Better quality 
Suit for text and code as no data lost
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45
Q

Lossy compression

A

Permanent loss of data
Cannot return to its original condition/not identical to original as data removed
Reduces file size more/significantly
Loss of quality more
Unlikely to be noticed by humans
For unnoticeable data / end users unlikely to notice the removal of data
E.g images, videos, sound
Where loss of quality is an acceptable trade off for smaller files
Cannot be used for text/code, makes unreadable /unable to execute code

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46
Q

Optical storage different types

A

ROM- data pre-written on them by manufacturer. Cannot be overwritten. Use:Music, films, software, games.

R- blank. Writes data but can only be written once.
Can be ready many times. Use:Copying data.

RW- can be written more than once

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47
Q

How to calculate number of bits

A

pixel width x pixel height x colour depth (bit per pixel)

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48
Q

Examples of sound files and video files

A 
sound= FLAC, MP3, WAV
video=   MOV, MP4, AVI
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49
Q

ALU (Arithmetic Logic Unit)

A

Performs logical and arithmetic operations (calculations and logical comparisons)

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50
Q

Fetch decode execute cycle detailed steps.

A

Program counter copies address of the next instruction to be run from RAM and stores it in the MAR. Program counter increments by 1. MAR stores the address of data. CU fetches data using address and stores data in MDR. Data is decoded by CU, and executed (e.g ALU does calculation)

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51
Q

What does the fetch decode execute cycle do?

A

TO PROCESS DATA
Instruction fetched from RAM memory.
Instruction decoded. Instruction executed.
Process is repeated.
CPU performs continuously.

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52
Q

CU (Control unit))

A

Controls and monitors communications between hardware attached to the computer. Controls input + output of data..
decodes instructions
Checks if signals have been delivered successfully.
Makes sure data goes to the correct place at the correct time.

data transfer between the registers in a CPU synchronized to the clock- co-ordinates all of the other components of the CPU.

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53
Q

Registers are

A

small fast memory storage with a set purpose
Accumulator, MAR, MDR, Program counter

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54
Q

Memory address register (MAR)

A

Stores address of
data that will be read/written/accessed/fetched/being processed/next to be processed

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55
Q

Memory data register (MDR)

A

Stores data that is fetched/written to memory/next to be processed data/data fetched from data address in the MAR

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56
Q

Program counter

A

Increments by 1
holds the address of the next instruction to be executed and copies it to MAR

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57
Q

Accumulator

A

Stores result of ALU

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58
Q

Things that can affect the performance of a computer

A

RAM (only if the computer runs out of memory space in ram, less reliance on VM)
Cores
Clock speed
Cache
Graphics Card
Sound card
Motherboard

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59
Q

Clock speed

A

number of FDE cycles run per sec/or given time. Measured in hertz
1 Ghz=1 billion cycles per sec
Higher Clock speed=more processing it can do per sec+instructions executed faster

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60
Q

Cores

A

. Allows multitasking/parallel processing. Each core can simultaneously execute instructions or run different parts of the program at the same time. Can process instructions independently of eachother
Double core processor eg:
Processes can be split up between processors and processed faster. More processes completed per second
E.G doubling the cores, doubles maximum processing the CPU can do
However, only improves performance if software is designed for multiple cores/depends on task

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61
Q

Why does having multiple cores sometimes not increase performance

A

-If software isnt designed for it :isn’t programmed to be split between more cores
-Depends on the task, some tasks cannot be split across cores
-Other factors besides from cores affect performance
e.g a quad core may have a lower clock speed, RAM size, cache size, than dual core

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62
Q

Cache

A

Stores frequently, recently and next to be used data
that can be accessed faster than accessing it through RAM
as transferring data to and from CPU and cache is faster than data to and from CPU and RAM.
Too much cache is detrimental as it will take longer for CPU to find the specific instructions in cache.
Increasing the cache, more data is transferred faster, makes CPU more efficient

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63
Q

Embedded system

A

computer system built into another device.

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64
Q

embedded system examples

A

Microwave, washing machine, dishwasher, oven, MP3 player, digital clock, calculator, coffee maker.

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65
Q

What is a embedded computer

A

single microprocessor that includes RAM, ROM and the CPU.
Its frequently used to control a device using simple controls.
Has a dedicated/limited purpose
Mostly designed to do one specific task
Simple/no user interface

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66
Q

General purpose computer

A

Designed to be able to carry out many different tasks
Consists of hardware and software
Flow of data is input>CPU>primary memory/secondary memory> output
Can have many applications
E.g access the internet, play games/videos/music, email, store and retrieve data

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67
Q

What does the CPU do

A

Processes data and instructions
FDE cycle
Controls computer system

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68
Q

Software and hardware

A

Hardware - physical components of computer
e.g CPU, hard disk, monitor, keyboard, mouse

Software- programs that run on computer

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69
Q

Buses

A

High-speed internal connection
Sends control signals and data between processor and other components(RAM memory, input/output devices)

Address bus- memory address
Data bus-data
Control bus- clock’s pulses, control signals

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70
Q

Von Neumann architecture

A

Data and instructions stored as binary and both stored in one memory (RAM), instructions fetched from memory serially (in order) one at a time
processor decodes+executes instruction, then cycling around to fetch next
Cycle continues until no more instructions

Input device>
CPU (control unit, arithmetic logic unit, registers)
Memory unit
Output device

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71
Q

network

A

set of connected computers and other devices in order to share resources

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72
Q

network benefits

A
  • can share files/ can work collaboratively on the same files
  • can share hardware resources
  • can access their files from any computer
  • can work together from different computers using instant messaging
  • centralised deployment of software to all computers
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73
Q

LAN

A

covers small geographical area
usually located on a single site
uses its/connected by own internal infrastructure/hardware
uses cables and radio waves to connect
Examples include home, small business, school networks
Generally the router connects the devices in a LAN together

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74
Q

WAN

A

covers large geographical area
uses external infrastructure/hardware
two or more LANS connected together
Uses cables. Telephone lines, satellites, radio waves to connect
Examples include ATM machines, the internet, international banking systems

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75
Q

similarities of WAN and LAN

A

allow devices to communciate with eachother
allow for shared periperhals
allow for remote maintenance

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76
Q

Speed of a network

A 
Bit per sec  (bps) 
E.g
Kbps
Mbps
Gbps
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77
Q

Bandwidth

A

How much data can be transferred over a connection in a given time

Bandwidth is shared/split between connected devices
E.g 54mbps per device if there’s 1 device, 27mbps per device if there’s two devices

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78
Q

Factors that affect the performance of networks

A

Wired/wireless connection
Bandwidth available
Number of users using the network at the same time
Number of data collisions and transmission errors
Interference (wireless)
Signal strength
Amount of data being transferred/applications being used
Server/CPU performance
Hub/switch

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79
Q

Client server model

A

Network relies on a central server
clients (devices) request services from server (e.g print services/ file services)
client is dependent on server to provide/manage the resources and info

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80
Q

Pros and cons of client server model

A

All files can be stored centrally
-user monitoring
-workers can access files from any computer
-all computers can update the central database/file
Backups are central
-all data is backed up each time
-individual computers do not need to backup their own data
Upgrade software centrally
-so you do not have to install on each computer individually
Central security (antivirus/firewall)
Centrally administered in one location
———————————————-
Central point of failure
Can be expensive to maintain and set up (e.g cabling costs, specialist staff.)
specilised required to set up server
central server needed

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81
Q

Peer to peer network model

A

No central server
Devices on the network have equal status
Files and data are shared between devices on the network

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82
Q

Pros and cons of peer to peer network

A

Easier to set up - simply be cabled together
easier to add new devices
No special software/specialist required to run
less initial cost and maintenance
If client goes down/fails, can connect to another peer (computers directly connected to eachother)
no reliance on the company’s server and it’s connection to the internet, computers are independant and equal - decentralised
no need to invest in lots of hardware and bandwidth and system likely more fault tolerant
no central software installation/devices can have different software
———————————————————————–
decentralised - no central file storage- files stored on individual machines - hard to find and located a certain version of file and files may become out of date.
Performance- as the number of connected devices increases, each computer is being accessed by the other so performance decreases
security problems - no central security so computer will need own security, and more vulnerable to social engineering as equal status and the malware can spread throughout the network
backup recovery- data is not centrally back up/updated so data have to be backed up individually and separately by user.

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83
Q

The hardware needed to connect stand-alone computers into a local area network

A 
Routers 
Switches
Wireless access points 
Network interface card 
Transmission media
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84
Q

Routers

A
  • Directs packets/data to destination in a network
  • Receives packets/data from network/Internet
  • forwards packets/data to other computers on a network/internet
  • connects (different) networks together e.g joins home network to Internet
  • Has public IP address for LAN
  • Designates private IP addresses to network nodes
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85
Q

Switches

A
  • connect devices together
  • receives data n directs traffic only to its destination
  • generates list of connected devices, receives signals
  • uses MAC address of devices connected to it
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86
Q

Wireless access points

A

-allows wireless devices to connect to wired network using Wi-Fi
usually connects to a router (via a wired network) as a standalone device/ integral component of router itself

-the further the device is away from WAP, signal strength weakens and possible wireless interference too (obstructions e.g walls)

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87
Q

Network interface card

A
  • Built into most devices, allows to connect to wired/wireless network
  • Allows data packets to travel to and from a computer
  • contains MAC address (physical hardware address)
  • allows Ethernet cable to be plugged into it
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88
Q

Transmission media

A

Ethernet (Cat 5e/ Cat 6) (twisted pair)
-A networking standard (uses twisted pair cabling or fibre optic)
-cheap, max transmission speed is up to 1gbps, max distance for reliable communication up to 100m
——————————————————————————————
Fibre optic
-often used with WAN or larger LANS
-expensive but fast, max transmission speed is over 40tbps, max distance for reliable communication is over 2km
-higher bandwidth, faster transfer speeds
-data can be transmitted over long distances without any loss of signal quality and as they transmit through light, they do not suffer from electrical interference
————————————————————————————————
Coaxial cable
-an older networking standard

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89
Q

internet

A

Inter-networking
giant mesh WAN
Worldwide collection of computer networks connected together

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90
Q

How a DNS (domain name server) is used in the process of accessing the website

A

-Allows you to type a web address into your web browser and translates it into an IP address
-Domain Name Service contains many DNS(domain name servers)
-DNS servers contain a database of domain names/URLs/website addresses, and their corresponding IP addresses
-The domain name/website address entered by a user is looked up in the DNS database tables to find the matching IP address
All packets are transmitted via IP addresses- therefore to access the server that hosts a website the IP address would be needed

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91
Q

Hosting

A

Website is placed on web server - known as hosting and a suitable domain name selected

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92
Q

Web servers & clients

A

main purpose of web server: host websites and deal with client requests
When website visited on client (device), a request to the web server is sent and then the website (stored as text HTML) is sent to the client and recreated in the browser
The web server is located via IP address

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93
Q

Client to web server process

A
  • website is hosted on a web server
  • website/web server has an IP address
  • browser sends URL to DNS
  • URL has a linked IP
  • DNS finds IP
  • ///if DNS cannot find the IP it passes request to higher DNS
  • ///if not found, return error
  • if found, IP address sent back to the browser/computer
  • (Browser) sends request to IP/web server using IP
  • web server processes request for website/page
  • web server sends webpage/file/data to the user
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94
Q

The cloud/ cloud computing

A

Computing done outside of your local network. Network of servers
Some servers run applications, some store data
Data is stored on the internet and remotely in large centre data servers across the world and managed by cloud providers

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95
Q

Advantages of cloud

A
  • efficient method of backing up data, saves time and money
  • Allows employees to work from anywhere
  • Environmentally friendly
  • Easy to increase availability of storage
  • Specialist network skills not needed, don’t need to employ more staff
  • Cloud third party provides security+backups, saves money on staff and software/hardware
  • Cheaper as don’t need own infrastructure
  • Increase storage
  • Access files anywhere in the world
  • Collaborate with others around the world
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96
Q

Disadvantages of cloud

A
  • Need constant internet connection
  • Reliant on third party to carry out security procedures,company itself still legally responsible if things go wrong, back up connection
  • Data vulnerable to hacking+other threats which the company have no control over
  • Issues regarding data ownership
  • Implications of data protection act
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97
Q

Star network topologies

A

Each device on network has own cable that connects to a switch/hub

hub sends every packet of data to every device/switch only sends packet of data to destination device

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98
Q

Advantages and disadvantages of star network topology

A 
If a device fails the rest of the network is unaffected
Simple to add new devices 
Good performance
Fewer data collisions
Easier to manage from a central point
------------------------------------------------------------------------------------
If switch dies, network dies
Can be expensive for cables
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99
Q

Mesh network topology

A

No central connection point
Each node connected to at least one other node and squally to more than one
Each node is capable of sending messages to and receiving messages from other nodes
The nodes act as relays, passing on a message towards its final destination

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100
Q

Mesh advantages and disadvantages

A

-no single point where the network can fail, if a node in the route fails the packet is sent a different way
-Can handle high volumes of traffic
-adding more nodes will not hinder the process as all nodes help to transmit data
—————————————————————————–
Expensive to set up, needs lots of cables
Difficult to manage and maintain

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101
Q

Wired

A

Ethernet/fibre optic/coaxial cables to form connections between nodes(networked devices)

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102
Q

Wireless (Wi-Fi)

A

medium range wireless technology used to connect devices together
uses radio waves transmitted by a WAP that has a wired connection to the internet

examples:
2.4Ghz - ultra high frequency
5Ghz - super-high frequency

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103
Q

Wired advantages and disadvantages

A

generally faster data transfer compared to wireless networks
much less likely to suffer from interference than wireless networks
more difficult for unauthorised users to intercept data
——————————————————————————–
expensive to install or reconfigure
users cant instantly move a device from one location to the another as there might not be a network connection available

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104
Q

Wireless advantages and disadvantages

A

Allows more flexibility with location as users can move around freely and still stay connected
cheaper to setup
new nodes can be added easily without interruption to the network
————————————————————————————
wireless transmission is slower than cabled
more devices/users could be connected e.g mobile phones//increase in traffic reducing bandwidth available for each user//insufficient bandwidth for users/demand
wireless can be limited by interference such as wall or other wireless users that disrupt the signal
radio signals pose a security risk as they can be intercepted by unauthorised users. to overcome this problem, messages need to be encrypted.

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105
Q

Bluetooth

A

Uses radio frequencies
No physical cable connections required
Designed to enable range of portable devices to connect to each other and to less portable hardware

Operates over short range (10~100m) which can be affected by obstacles
Devices do not need to have a direct line of sight to connect

Common uses:
Sharing data files between mobile phones
Sending audio to Bluetooth speakers

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106
Q

Bluetooth advantages and disadvantages

A

-Low cost to set up
-Uses relatively little power compared to other types of wireless connection
-you can easily set up Bluetooth networks with other Bluetooth enabled devices
————————————————————————
Short range
Low level of security
Low data transmission rate

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107
Q

IP addressing and IP Address

A

IP addressing is
data travelling on a network are sent as packets
each device on the Internet has a unique IP address which is used as an “address” to send the packets
——————————————————————————————
IP Address is a
unique ID
can be changed/allocated as needed
configured by software
used for routing across the internet or Network

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108
Q

IP address IPv4 system

P address IPv6 system

A

4 bytes long
4 sets of 8 bits
Values separated by dots
normally written in denary 0-255
allow for just over 4 billion unique addresses
———————————————————————————————
8 groups of 4 hexadecimal digits
8 sets of 16 bits
values separated by colons
allows almost 80 octillion unique IP address

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109
Q

MAC address

A

consists of 12 hexadecimals/normally written in hex
48 bits / 6 bytes long
configured in hardware
only used within a LAN
fixed/cant be changed
unique serial number assigned to each network interface controller
unique to device, allows network to uniquely identify any device; even when a dynamic IP address is assigned using DHCP(dynamic host configuration protocol)
The router assigns IP addresses based on the mac address

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110
Q

network protocol and protocol

A

Protocol: set of rules for data transmission and communication between hardware
Network: set of rules for data transmission across a network
for how computers should communicate//how data is sent/received/transmitted on a network
defines standards + rules for data transmission

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111
Q

TCP/IP

internet protocol suite

A

set of protocols used over the internet
organizes how data packets communicated,makes sure packets have:
source- which computer the message came from
destination- where the message should go
packet sequence- the order the message data should be re-assembled
data- the data of the message
error check-the check to see that the message has been sent correctly
——————————————————–
TCP splits data into packets, numbers them, reassembles packet and orders them at other end, resends lost messages, detects errors

IP locates destination and routes the packets over the network via routers

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112
Q

Packet switching process

A

request split into packets
each packet is given the address and a number
and consists of two parts (header - IP addresses, number, total number of packets, protocols used) and payload (message itself)
packets are sent across the network
packets are received by the host server
server checks if all packets have arrived
if they have not: timeout is sent to request the packets are resent
if they have: packets put in order

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113
Q

Network protocols

A

HTTPS (Hyper Text Transfer Protocol)-Viewing a website using a web browser. Uses secure socket layer. Encrypts data and connection itself.

HTTPS (Hyper Text Transfer Protocol Secure)-Viewing a website using a web browser but Encrypts the connection

FTP (File Transfer Protocol) - Used for sending or retrieving files to or from a remote server or computer. Uses a client-server model /sends from client to server, sends from server to client

POP-retrieves/accesses/downloads email from a mail server
removes the email from the server and transfers it to the device

IMAP-Retrieves and downloads a copy of an e-mail from the server, Allows synchronisation/management of account

SMTP-sends/forwards/transmits e-mail from one server to another
or/and from an email client (device) to a server

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114
Q

layers (4 layer model)

A

a division of network functionality

application layer- encodes/decodes the message in a form that is understood by the sender and the recipient. HTTP, HTTPS. SMTP, IMAP, FTP, POP

transport- breaks down the message into packets. Each packet is given a packet number and total number of packets. Recipient uses this info to assemble packets together in correct order and to see if there’s any missing packets. TCP, UDP

network- adds the sender’s IP address and that of the recipient/ The network knows where to send the message, and where it came from. DNS. IP

data link - enables the transfer of packets between nodes on a network, and between one network and another. Operating system drivers and NIC, Ethernet/Wireless LAN

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115
Q

advantages of using layers to construct network protocols

A

splitting networking into layers means each layer is self-contained - does not need to consider what the other layers do - each layer has its own purpose and can be programmed individually
allows different developers to concentrate on one aspect of a network
a layer can be removed or modified without affecting other layers
promotes interoperability between products from different vendors/systems
individual protocols are smaller/simpler to manage
different layers can interact with different hardware

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116
Q

A device not connected to a network is called

A

A stand-alone

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117
Q

Virtual network

A

Network that can securely connect
Geographically unrelated computers
Via the internet

Virtual network servers create a network that has no direct physical connection but allows file sharing and communication
Enable users at home to connect to the organisation’s data and facilities and work at home

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118
Q

Latency

A

How long it takes a message to travel from one device to another across a network
Low latency= few transmission delays
High latency- more delays, longer to transmit data

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119
Q

Transmission errors

A

When two devices on a network try to communicate simultaneously along the same communication channel. Their signals collide and the transmission fails.

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120
Q

Role of web client and web server

A

web server:
Control access to a centralised resource (definition of a server)
Stores content and layout data for web pages
Receives+processes requests for web pages
——————————————————————————–
web client
Sends requests for web pages
Sends DNS requests for IP addresses
Displays the result of web requests

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121
Q

Encryption process of HTTPS

A

Client requests HTTPS session
Certificate sent to client from the server
Client creates sesshion key
Encrypted session key is sent to the server
Session key is decrypted with private key
Session encrypted with session key

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122
Q

standard

A

all manufactureres/developers agreeing to follow something when working in a specific area
so devices/applications are able to communicate with eachother even if created by different vendors
e.g protocols. devices communicating over network must use the same protocols to allow them to understand eachother.

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123
Q

Malware

A

Piece of software/code/a program
That replicates itself and causes damage by editing or deleting files

Prevent by running anti malware software and not downloading from unknown sources or clicking on unknown links

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124
Q

Virus

A

malicious software embedded in a program that replicates itself and causes damage to the computer by deleting/altering files/data

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125
Q

Trojans

A

Programs which pretend to be legitimate but are malware. Disguised as email attachments often. Cannot spread by themselves and deceived a user into installing the program

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126
Q

Worms

A

Replicates themselves and become part of other programs and cause damage by deleting or modifying data. Often spread through emails.

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127
Q

Ransomware

A

Prevents access to your files unless a random is a paid

Prevent by: anti-malware, firewall

128
Q

Spyware/keylogger

A

Piece of software/code/a program
That records actions/keys presses and sends this data to a third party for analysis

Prevent by: running anti-spyware/malware software, firewall

129
Q

Social engineering - people are the weak point

A

Person behind the weak point of the system (for example by deception)
Prevent by: strong passwords, checking no validity of sources

130
Q

Phishing

A

Email link directs user to fake website that collects personal data when clicked
Prevent: network policy, firewall

131
Q

Pharming

A

A piece of code installed that redirects user to fake website that collects personal data
Prevent by: anti malware, firewall

132
Q

Staff being the weak point

A

Brings in corrupted files via medium
Downloading infected files from the internet
Sending/sharing sensitive data with third parties
—————————————————-
Counter measure
Not allowing/stopping external devices being used on the network
Blocking/restricting access to insecure websites
Blocking/restricting access to USB ports/email/internet/printing

133
Q

Brute force attack

A

A program attempting all possible password combinations of characters until the correct one is obtained

prevention: strong passwords: network policy, locking out after several incorrect attempts

134
Q

Denial of service attacks

A

When a computer/many computers are used to prevent a server from performing its task. This is done by bombarding the server over and over again with requests. Eventually the server is tied up tying to handle all the DOS requests, making it very difficult for the server to respond to legitimate requests.

135
Q

data interception

A

data transmission being read by unauthorized users/programs

Where data is intercepted during transmission
Done using software - packet sniffer
Examines data packets as they are sent around a network/across internet and the information gathered is sent back to a hacker

prevention: firewall, encryption

136
Q

SQL injection

A

Where SQL code is entered as a data input. Many databases uses SQL code to interrogate the data and maintain the structure
SQL code can be inputted as data which can cause errors or unintended operations

137
Q

Penetration testing

A

determine how resilient a network is against an attack
authorised users probe the network for potential weaknesses and attempt to exploit them
Software that enables network managers to test resilience of network also available

138
Q

Anti malware software

A

Prevent, detect and remove malware from the system
Scans through all the files on the computer and checking them against a list database (definitions) of known malware

Reactive - can only detect, prevent and remove known malware
When new malware is introduced, it has to be updated. Less protection= not updated
Includes anti-virus, anti-phishing tools, anti-spyware software

139
Q

Firewalls

A
  • protects the network by stopping unauthorised access and unwanted incoming and outgoing transmissions of packets
  • blocks port and monitors incoming and outgoing data packets
140
Q

Network policies

A

Rules that define acceptable use
E.g log in hours time and from certain computers, to ensure attempts entered in the system are likely genuine

Network manager should have an acceptable use policy:

  • secure strong password which meets specified conditions
  • passwords are changed on regular basis
  • unauthorised equipment cannot be connected to the network EG usb sticks, smartphones, tablets
  • levels of access are given, allows only authorised users to access sensitive data
  • regular backup procedure
  • disaster recovery procedure
  • regular maintenance, software upgrades, security patches to equipment
  • prevent physical access to server
  • up-to-date anti malware software and firewalls
141
Q

User access levels

A

Different levels of access, each user can only access the files they need,

determines the facilities (software, mail, internet, documents and data, installing/removing software, maintaining other user’s accounts) they have access to,

restriction limits the action the user can take to reduce potential threats and prevent:
accidental damage, installation of software, accessing specific network drives, prevent files from being modified/deleted, making changes to system

142
Q

Passwords

A

Protects user accounts, ensure only authorised people can access the network

Strength set in policies to prevent brute force attack

Ideal: at least 8 char, 1 uppercase, 1 number, 1 special char

Not easy to guess= secure but also hard to remember

143
Q

Encryption

A

Uses a algorithm to scramble up data
turns text into cypher text
if accessed by unauthorised user, cannot be understood.
renders any intercepted data useless
Keys used to encrypt and decrypt the data

144
Q

Physical security

A

Not allowing physical access to a network by locking doors/key cards or any physical security procedure

145
Q

Asymmetric encryption

A

Algorithm that generates two keys
Public key- encrypt data
Private key- decrypt data

146
Q

Network attack forms

A

Active- modify/delete data on network or prevent it from operating correctly. e.g DOS
Passive- monitors network to gain info
External- someone outside organisation attempts to hack
Internal- someone within organisation attempts to hack

147
Q

Network forensics

A

Monitoring traffic on network
Regular intervals- copy transmitted data packets
Copy is stored for analysis, info can help identify invasive traffic or determine where data is being sent

148
Q

System software

A

Software that governs the computer system, helps run computer
Includes operating system, drivers and utility

149
Q

What is an operating system

A

A suite of programs that managea and controls a computer. Applications software allows a user to perform tasks

150
Q

Examples of operating systems

A

Windows-less secure-mainly GUI-closed source-beginners
Apple IOS-secure-GUI-closed source-beginners
Linux-secure- mainly CLI- open sourced- expects
Android OS- less secure - GUI- open sourced- beginners
Apple MacOS- secure- mainly GUI- closed sourced- for beginners

151
Q

All operating systems have something in common

A

Interface that manages drivers, files and users

152
Q

Role of operating system

A 
Provide platform for software to run on
Manages memory
Mange’s peripherals used by system 
Provides interface between computer and user
Determine look and feel of computer
User, file management 
Multitasking
153
Q

User interface

A

Programs/suite of programs that allow a user to interact with the computer

154
Q

Examples of user interfaces

A

GUI
Command line interface
Mobile user interface

155
Q

GUI

A

Graphical user interface
Visual way of user interacting with computer
Sometimes known as WIMP (windows, icons, menus, pointers)

  • easy to understand
  • beginners use
  • aesthetically nice visual
  • slower
  • takes up more memory
  • less flexible, does not have same level of functionality as CLI
156
Q

Mobile UI

A

Easy to use

Needs a lot of processor power

157
Q

CLI

A

Command line interface
Using code to give instructions/interact

  • Complex to understand
  • experienced users
  • less appeal as it’s text
  • takes up less memory
  • greater flexibility of use
158
Q

Multitasking

A

Slice of time for each programming running at a fast speed
Means being able to run more than one program simultaneously
Allow several programs to run side by side

159
Q

Memory management

A

So more than one program can be run at the same, more than one document can be opened at the same time

OS determines how much memory the program requires, and allocates enough space to hold it and it’s documents. When the program is closed, the allocated space are freed up for use by other programs.

Freeing up, VM, transfer data, buffering(temporary storage area for processes to dump outputs and set aside memory so process can store temporary data. When buffer is full, processes need to wait), diffferent processes have different areas of memory so they don’t collide,

160
Q

Peripherals and drivers

A

Peripherals:
Output/input hardware devices connected to the computer, e,g microphone and printer
—————————————————
device drivers:
Computer programs that controls and operates peripherals so other programs can access the device’s functions)
Contains instructions on how to control device
Each connected device has its own drivers
Advantages: any device can be used within the operating system as long as a driver is available for it, drivers can be updated to give better performance or to remove bugs

161
Q

User management

A

Block content, admin rights, deleting creating accs, access rights to certain files or programs, set password protection

Manage users. Allows individual users to be created/deleted, access levels (standard user rights and administrator rights), auditing (log of files a user creates accesses edits and deletes)

162
Q

File management

A

Manage data/files
File handling and maintenance

E.g
Place files into folders, rename folders and files, copy folders, move files, delete, search, set permissions/access rights on files, create, open, sort files

163
Q

What does utility software do

A

Help for computer to maintain computer system

164
Q

Utility software Includes

A

encryption software
defragmentation software
data compression software
backup software

165
Q

Encryption

A

Disguises data by using algorithm to scramble up data into cyber text
So if accessed by someone other than the intended recipient, it is not understandable
Keys can be used to encrypt/decrypt the data.
Public key used to encrypt data
The private key can be used to decrypt data.

166
Q

Defragmentation

A

Files/ programs opened on hard disk are stored as series of segments. At first, segments run together in sequence. When program closed, segments are cleared up, leaving free space for next program. Over time, files become fragmented. A fragmented disk takes longer to read from/write to so makes computer run slower

Defragmentation takes fragmented files and rearranged the segments so that they run contiguously. This decreases read/write time. Speeds up computer performance

167
Q

Compression software

Lossy/lossless

A

Reduces the file size of files and makes smaller
So less storage space used
Faster transmission
And to store more files

Lossless will not remove data permanently
Lossy is permanent deletion of unnoticeable data

168
Q

Back up software

A

to prevent data loss, regular copies of data should be done

full backup-all data files and software are copied(takes a significant time to back up entire system, takes up lot of storage space)

incremental-only copies data that has been changed since the previous backup (less time to backup, take less memory space, needs a full backup done before incremental backups can be done)

169
Q

What is software

A

The programs that run on the computer hardware

170
Q

Application software

A

Help user to perform tasks

171
Q

Auto update software (ultility)

A

Checks Internet for new versions of software/OS
Downloads and installs without user interaction
helps keep software running efficiently on new hardware, fixes bugs and adds new features.

172
Q

firewall (ultilty)

A

blocks port and checks for incoming packets of data, protects a network from unauthorised access. examine ingoing and outgoing traffic, helps prevent/restrict unauthorised traffic over a network/external source.

173
Q

anti virus/malware (ultilty)

A

a program/set of programs that prevent, detect, and remove malware/viruses and other malicious software

174
Q

Diagnostic software

A

attempts to detect/resolve items that are not working correctly

175
Q

system information (diagnostics)

A

displays important data about the current state of the computer

176
Q

Computers in the workforce

A
  • Improves effiency, speeds up, more confident, improve productivity
  • reduces labour and wage costs, lower prices for consumers + business
  • reduce strain on workers and reduce the need to work on repetitive and tedious environment
  • potential to save lives
  • More knowledge
  • Online businesss, oppourtinies for people
  • less people viewing the data, more secure, people are the weak point
177
Q

Ethical issues of digital tech on wider society

A
  • ill health, distractions, addiction
  • digital divide
  • social divide
  • confidential data
  • social pressure on parents, children, public to buy and upgrade
  • high cost
  • storing+access to personal info
  • rules/terms set up before people can join
  • consequences for misconduct e.g cyber bullying
  • plagiarism
  • communication of inappropriate materials for students/school/teacher
  • backing up to preserve/save data
  • gaining parental consent for communication online
  • E-safety
  • acceptable use policy
  • People lose jobs. Replaced
  • ethics of decisions made by algorithms, could affect people’s lives.
  • censorship+ pushing a certain ideology. Propaganda
178
Q

Legal issues of digital tech on wider society

A

Data protection act
Rules of DPA
Sensitive data hacked
Keeping data secure, need for firewall, anti-virus
Accountability
Methods of restricting access
Intellectual property/copyright/liscences
-Allows people to commit crimes remotely and opens up more opportunities for illegal activity

179
Q

Cultural issues of digital tech on wider technology

A

Desire/need to own newest device to fit in with peers
May have new features that users require for work/leisure
Demand of jobs in digital tech fields
Exclusively online services/businesses
High dependence on computers and tech by people
communication online - not real life

180
Q

Environmental issues of digital tech on wider technology

A

The type of devices that are disposed of
Modern phones poorly designed for durability
Phones’ hardware not upgradable/replaceable
e-waste shipped to third world countries with lower environmental standards
-people dispose of their devices in landfill even if they are in good working order)
Some equipment is also sent abroad to be disposed of
Leads to excessive landfill (abroad and internal)
Toxic waste released into land, ground water, air, contaminating it.
Waste of resources
Precious metals in phones
Electricity required to power devices - using up fossil fuels + greenhouse gases + climate change

181
Q

Digital items and physical items

A 
Digital:
Less/no plastic/paper/raw materials used in manufacture// no need for packaging // less waste less electrical power needed to manufacture 
No petrol used to distribute/collect
Smaller carbon footprint 
Fewer dusk may need to be manufactured 
Fewer factory emissions //less pollution
Old versions will be thrown away 
——————————————————
Physical items 
Plastic /paper are used in manufacture 
Increase in waste 
Old versions will be thrown away 
Uses petrol/creates emissions to distribute
182
Q

Privacy issues of digital tech on wider society

A

Tracking of IPs/devices
Social media
Unwanted images and videos of people may be out online
Risk of threats e.g phishing/pharming/virus
-stealing/copying/transmission of private data
-not all countries subjected to same privacy laws, data could be stored somewhere there

183
Q

Legislations

A

Data Protection Act 1998 -control ways data of living people is stored+ processed
Computer Misuse Act 1990 offence to access/modify computer material without permission
Copyright, Designs and Patents Act 1988- covers the copying/use of other people’s work
Regulation of Investigatory Powers Act 2000- regulates surveillance and investigation, and covers the interception of communications
Freedom of Information Act 2000 -allows public access to data held by public services (e.g the council) unless data is sensitive/too costly/time consuming

184
Q

Data protection act

A

Data is collected/exchanged/processed fairly and lawfully
Using data only for its specific lawful purpose
Collecting only adequate, relevant, needed and not excessive data
Data of customer must be accurate and up to date
Data should not be kept longer than necessary for its purpose. Once warranty expires, data should be rid of.
Data should be processed with accordance of people’s rights and consent. Rights to request a copy of data/prevent marketing/correct data held about them/right to be forgotten.
Data should be stored securely and safely. Security measures, protection and legal obligation.
Data should not be transferred outside of EEA (countries in European Economic Area)

185
Q

Computer misuse act 1990

A

No unauthorised access to data
No illegal activity with the unauthorised accessed data or the intent to
No unauthorised modification/deletion of data

186
Q

Copyright, designs and patents act 1988

A

Give creator’s exclusive rights and ownership over their work and they can determine who’s allowed to use it, how it’s distributed/published/sold.
Licence- copyright holder can grant permission for creation to be used

187
Q

Creative Commons licence

A

-Allows free distribution
-Can choose to restrict use/edit/share/distribution/copying/displaying of original
-Work is still copyrighted/others cannot claim it as their own
Different types:
-No-derivative: can set that if others edit it, they cannot redistribute it with the edits
-Attribution: having original creator’s name on it if re-used//referencing/must be credited)
-Non-commercial use:others cannot sell/profit from the work //personal use only

188
Q

Different types of Creative Commons licenses

A

Attribution - copyright owner must be given credit
Non-commercial- no profit can be made
No derivative works - cannot be modified
Share-alike - must be under identical licence as original

189
Q

Software licenses (open source and proprietary)

A

Open source
The source code is distributed with the software
Can adapt it/add features to the program
The customer can redistribute the source code (with the same licence/restrictions)
Free of charge
———————————————————-
Closed source - proprietary
Source code not made available
Only compiled code is published
Licence restricts the copying/modifying /distribution of the software
Can charge customers to earn a profit
Can restrict what users can do
Protects/copyrights her source code so it can’t be copied/modified/redistributed

190
Q

Abstraction 5

A

only focusing on details important to problem trying to be solved. unnecessary details are left out

  • simplify problem, reduce complexity
  • more efficient and quicker
  • save storage space and less resource intensive
  • reduce time taken to program, less developing time
  • key info focused on so makes product better
191
Q

Decomposition

A

breaking down larger complex problems into smaller sub problems

  • easier to solve as smaller
  • can be created independent of other problems, tested independently, combine to produce full problem
  • can reuse in other problems
192
Q

Algorithmic thinking

A
  • getting to a solution
  • by identifying the steps needed
  • break complex problem into manageable small problems
  • designing simple steps to solve each
193
Q

Advantages of pseudocode

A
  • tool for algorithmic thinking, enables programmers to design/describe algorithm syntax independent (does not matter if syntax errors)
  • convenient way of designing algorithms to aid thinking logically as easy to understand and changes to design can be done easily
194
Q

Trace tables

A
  • see sequence of which program executes at to understand how it works
  • used in testing code to see how variable value changes as code executes to identify logic errors
195
Q

Linear search

A

No need to be ordered,easier to program, less efficient

Starts at the beginning of the data set and each item is inspected in sequence until a match is made
If item found, search ends. Else, next element inspected until all items have been searched. If nothing found by end of algorithm, then false is returned

196
Q

Binary search

A

Sorted list only, More efficient, harder to program, resource heavy of memory use, faster as half of data set is discarded after single check

-Checks position of middle, sees if it’s the object being searched for -if not, discards data set of the irrelevant side (list size halved). Goes to new midpoint and process repeats. Uses divide and conquer. If item not in list, item displayed as not found

197
Q

Bubble sort

A

Easy to implement, inefficient, for small data sets

Sorts and orders list of items
Starts at beginning of list. Compared item to next item. Swaps if out of order. Algorithm finishes when no more swaps need to be made
When first pass is completed, can be sure that largest item is at end of the list.

198
Q

Merge sort

A

Harder to code, more efficient, can work on multiple lists at same time. large data sets. Creates two/more identical sub problems from largest problem, solves them individually, constant running time

Divide and conquer. Data set is repeatedly split in half until each item is in its own list individually.
Adjacent lists are compared, sorted into order and then merged back together which repeats, ultimately recompiled into a sorted list.

199
Q

Flow chart

A
  • Displays an algorithm in diagram form
  • using symbols and arrows
  • to show the flow of information
  • show step by step solution to problem
200
Q

Pseudo code

A

Structured use of English

used to define steps needed to solve a problem

201
Q

Insertion sort

A

More efficient+harder to code than bubble sort, less than merge sort. Work best with smaller data sets

Second value in list gets compared to value to its left. If value greater than left, no changes made. Wall to sort sorted and unsorted side. Values are compared in turn and get compared to sorted side. Value repeatedly moved left until meets a sorted value that is less than it. Repeats until end of list reached.

202
Q

Algorithm

A

A set of instructions for solving a problem or completing a task

203
Q

Structure diagram/design

A

Decomposition of problem into sub problems
easier to change/write/test/maintain
solution reached faster
less prone to errors during development
multiple programmers can work on program at same time

204
Q

Bubble sort flag

A

Flag=false/true
If there is a swap during the pass then flag changes = hasn’t been fully sorted
Flag stores whether any swaps had been needed in the pass
It’s a variable which stores a Boolean

205
Q

Flowchart symbols functions

A 
Process=action
Subroutine=calls a subroutine 
Terminal=start/end of process  
Decision=true/false 
Line= represents flow of one component to the next
206
Q

Bubble sort worst case scenario

A

Max passes of worst case scenario = n-1

207
Q

Disadvantages of pseudo code

A
  • hard to see how program flows

- time consuming to produce

208
Q

Flow chart advantages and disadvantages

A

-easy to see how program flows
-follows an international standard so it promotes interoperability. Easy for any flow diagram user to pick up a diagram and understand it
—————————————————
-diagrams can become huge and difficult to follow with a large program
-any changes to the design may mean a lot of the diagram has to be redrawn

209
Q

the 3 programming constructs/logic structures

A

selection
iteration
sequence

210
Q

what are programming constructs/logic structures used for?

A

they control the flow of a program

211
Q

Nesting

A

When one programming construct is included within another
-Reduces amount of code needed
-Simpler to debug and edit
E.g selection nested within condition controlled loop iteration

212
Q

Nesting examples

A

Nested selection : Number of possible paths at decision point can be increased by including one selection within another
Nested iteration: two count controlled loops (one within another)

213
Q

Selection

A

Section of code is only ran if it meets a condition which determines which path running program takes

Results of decision decided which path the program takes next

214
Q

Sequence

A

The order of which statements are executed- statements are executed one after another from top to bottom

Important as carrying out instructions in wrong order leads to program performing incorrectly

215
Q

Iteration

A

Repetition of a execution of a section of code when the program is running

  • Simplifies program, fewer lines of code,less error prone
  • more flexible, can just change loop value to change number of iterations
216
Q

Two types of iteration

A

Count-controlled iteration: repeatedly executed section of code a fixed number of predetermined times
Condition- controlled iteration: repeatedly executed a section of code until condition is met

217
Q

DIV and MOD

A

DIV gives the whole number //

MOD gives the remainder %

218
Q

Data type

A

Integer
Real
Boolean
String/character

219
Q

Where might casting be useful for

A

convert data type of variable to another
e.g for calculations, displaying
ints and floats cant be concatenated
numbers held in strings cant be used in mathematical operations

220
Q

Concatenation and manipulation of strings

A 
concatenation=joining strings together
e.g word=sentence+"Computer"
---------------------------------------------------------------------------------------
manipulation of strings
topic=topic.lower
topic=topic.upper
sentence="NadiaIsABean"
sentence[2] would give the output "d"
sentence[0,3] would give out "Nad"
sentence[2,3] would give out "dia"
len(sentence) would give out 12
221
Q

Variable and constant

A

Variable- named storage location that holds a value that changes
Constant- named storage location that holds a value that doesn’t change

222
Q

Subroutines

Small section of code that performs a specific task, can be called whenever needed

A
  • Breaks down problem/program
  • Structures program
  • Makes easier to maintain/design/create/test/read/debug as shorter
  • Reuse code (in different programs) -quicker to develop new programs
  • Build on existing work/use library of subroutines
  • Avoid repetition of code in the same program
  • Makes program shorter/smaller
  • Subroutine called instead of copying and pasting
  • Errors will not have been copied to other areas of the program
  • split up into a team to suit developer skill set to work on different sub program at the same time, develop/test separately
  • Allows for abstraction, remove complexity
  • Can be by programmers who do not need to understand how they work
223
Q

Procedures and functions

A

Function - returns a value

Procedure- doesn’t return a value

224
Q

SQL
Structured queried language
Used for interrogating a database

A

SELECT (variable) FROM (table) WHERE (criteria)

  • is the wildcard that stands for “all”/shows all fields from a table

If selecting multiple then it would be separated by comma
E.g
SELECT ItemName, Phone

225
Q

File appending

A

file=open(“filename.txt”)

file. write(“what you want to write to file”)
file. close()

226
Q

2D arrays append

A

arrayname. append (item)

arrayname. delete (item)

227
Q

File printing

A

file=open(“filename.txt”)
print ( file.read())
file.close()

228
Q

File search (first 8 characters of each line of file)

A 
search=input("What are you looking for")
file=open("filename.txt")
for line in file:
        if line[0:8] ==search:
        print("item found")
print("search finished")
file.close()
229
Q

global variable

A

can be accessed/changed throughout program

programmer has to declare the variable is a global

230
Q

Database

A

Persistent organised data store of related data to make it easier to search for info

231
Q

Maintainability

A

Making sure code is easily readable and understandable so its easier to look after, update, develop over time

allow other programmers to understand code
through comments, indentation, constants, modularising, sensible variable names

232
Q

Purpose of defensive design

A
  • anticipating every possible way user could misuse system/device
  • methods placed to eliminate/minimise misuse
  • so program continues to run correctly no matter the actions of the user

-protection against unexpected user inputs/actions, maintainbility, minimising/removing bugs

233
Q

Input sanitisation

A

cleaning up unwanted input data like removing suspicious or special characters to prevent SQL injection (code inputting that allows someone into a system)

234
Q

Verification

A

checking data has been entered correctly
double entry
visual check

235
Q

what is visual check

A

double checking data input by looking at it
proof-reading/data is compared to source document
compared by human
if discrepancy is found, data is re-entered
e.g looking over a CV before sending it

236
Q

what is double-entry

A

data is entered twice to check both sets of data match up
compared by computer, human
if a discrepancy is found, the data entry operator is asked to re-enter data
e.g
please enter password: NADIAISABEAN
confirm password: NADIAISABEAN

237
Q

Aunthentication

A

ensuring only allowed/authorised users can gain access to the system
usernames/passwords, fingerprint, iris, physical authenication, email authentication, capture, two-factor authenication

238
Q

Validation

A

Checking whether data is allowed and follows criteria

cannot ensure that it’s a wrong value, only ensures data is reasonable
e.g birthday date jan 1 2000

239
Q

Check digit

A

Uses additional digit - check other data correct
Mathematical algorithm - calculate value from other data and value is compared to check digit to check that tracking code has been entered correctly

Why is a check digit used?
Used to ensure a range of numbers have been entered correctly. Detects errors on identification numbers.

240
Q

Format check

A

checks data is in the right format

241
Q

Length check

A

checks the data isn’t too short or too long by checking how many characters there are

242
Q

Lookup table

A

Looks up acceptable values in a table

243
Q

Presence check

A

checks data has been entered into a field

244
Q

Range check

A

checks a value falls within a specified range

245
Q

Comments

A
  • to explain the key functions/sections
  • inform of any errors/issues
  • stop line of code from executing
246
Q

Indentation

A

to show where constructs/sections start and end

e.g indenting in IF statement/loops

247
Q

Naming variables sensibly

A

to enable programmers to understand the purpose of each variable

248
Q

Using constants

A

so specific data isnt changed

and so numbers can be updated easily

249
Q

purpose of testing

A
  • finding errors so they can be fixed before use so program works as intended+does not crash
  • ensuring end results meet user requirements
  • making sure there are no problems when released so system gains user/customer confidence
250
Q

iterative testing

A

testing during the development of code

251
Q

final/terminal development

A

testing after the majority of development has been completed/ testing before release

252
Q

describe the difference between iterative testing and final testing

A

iterative testing is testing during the development /repeatedly testing after/while making changes
final testing is done after iterative testing/when development is almost complete

253
Q

What is a error

A

causes the program to run incorrectly

logic, syntax or runtime

254
Q

Logic error

A

contains an error
but still runs/ doesnt crash
an error that results in the incorrect output/unexpected result

255
Q

Syntax error

A

error that breaks the rules of the programming language

will not execute

256
Q

Runtime error

A

error that occurs when program/code runs and causes program to crash
usually because of running out of memory

257
Q

Test data types

A

normal- data program expects and accepted
boundary- correct type of valid data on boundary (on the maximum or minimum range value) that should be accepted
invalid-data program expects but beyond the accepted range so should be rejected
erroneous data- data the program doesn’t expect and should be rejected by computer system

258
Q

Testing tables

A
  • to find errors in the code
  • see if program outputs expected outcome
  • Tests normal, invalid, erroneous, boundary data
259
Q

Basic authentication

A

make a request for a webpage by typing in URL
Server responds with an error, requesting authentication details encoded in request
Again the server checks the details and sends the page request or another error

260
Q

Why data is represented in computer systems in binary form

A

Binary is representation of presence of electricity
On=1=present
Off=0=absent

261
Q

Logic gates

A

Logic gates take inputs and covert them to an output

Digit 0 or 1 is stored in transistors in processor

262
Q

Boolean operators

A

AND- conjunction
OR- Disjunction
NOT- Negation

263
Q

An interpreter

A

translates code line by line

every time program is ran

264
Q

A compiler

A

translates code in one go all at once

265
Q

interpreter advantages

A

stops when error is found- can be used for debugging
portable (only need source code and interpreter on any device to run)
execution control
less memory as instructions are executed as soon as they are translated and are not stored for later use

266
Q

Compiler advantages

A
  • creates executionable file that can be distributed
  • executional file executes very fast
  • once compiled, doesnt need to be compiled again
  • executionable file is in machine code, end user cannot see source code so cannot steal/modify code
267
Q

interpreter disadvantages

A
  • slower than the executionable file that compilers create
  • runs slower as processor has to wait for each instruction to be translated before it can be executed
  • source code and intepreter required to run
  • users can see source code and steal it
  • code is not optimised
268
Q

Compiler disadvantages

A
  • long compiling time
  • if there is a error, would need to fix the error and compile it all again as compiler only reports error at the end.
  • harder to test
  • if its stopped during the compiling time, have to restart it again
269
Q

High level language 7

A

close to natural human language
English-like structure and syntax
needs to be translated before it can be ran
easily understood/program/learn
portable to different systems
one high level command equates to many machine code instructions
programmer can focus on problem instead of considering underlying hardware

270
Q

Low level language 9

A

assembly code
machine-specific
Opcode and operand
uses mnemonics (abbreviation of code)
1 assembly code translates to 1 machine code
needs to be translated before it can be ran
used in device drivers
when fast execution is required
can be used when there is limited memory space
Harder to understand/program/learn

271
Q

machine code 6

A 
binary instructions
Code for CPU to execute
difficult for humans to understand
has opcode (actual instruction) and operand (value instruction uses/manipulates)
does not need to be translated
not portable to systems
272
Q

translators

A

Convert source code to machine(binary)
enable code to be executed
processer can understand/run only binary

273
Q

Assembler

A

A program that translates assembly code (low level) into machine code

274
Q

IDE

A

Integrated development environment

Includes: editors, error diagnostics, run-time environment, translator

275
Q

Editor

A

To enable programmer to write source code to entered/edited

276
Q

Run time environment

A

To enable to the program to be run

Check for run-time errors/test the program

277
Q

Error diagnostics/debugging

A

To display information about errors (syntax/run-time) location of errors

278
Q

Debugging tools

A

Syntax completion- suggests/corrects code - quicker to type/less errors

Keyword highlighting/colour coding keywords/pretty printing- colour commands/variables - easier to read/identify errors

Breakpoints- to stop/pause program execution at a specific point - easier to identify/correct logic errors

Stepping- to execute program line by line - easier to identify/correct logic errors

279
Q

Units

A 
Bit (0 or 1)
Nibble (4 bits) 
Byte (8 bits)
Kilobyte (1,000 bytes or 1KB) 
Megabyte (1,000 KB)
Gigabyte (1,000 KB) 
Terabyte (1,000 GB) 
Petabyte (1,000 TB)
280
Q

What is meant by a bit

A

the smallest representation of data, 1 or 0. Single binary digit

281
Q

How data needs to be converted into a binary format to be processed by a computer

A

Computers consists of transistors/switches/logic circuits/ gates which only have two values/ on or off/1 or 0/ open or closed
Circuit only needs to check for two states/ uses switches electricity flowing or not flowing/on or off/1 and 0

282
Q

Computers consist of

A

Binary numbers, 1 or 0
The circuit only needs to check for the states 1 or 0
Only understands binary

283
Q

What is a overflow error

A

When we add or shift a number and it becomes too big for the register , number can’t fit into 8 bits and is greater than 11111111 and there is a extra carry/bit
loss of accuracy

284
Q

Hexadecimal

A

One hexadecimal is equal to one nibble
made up of 4 bits per hex digit
used in: defining colours in graphics software, represent MAC addresses , displays address, for checksums

285
Q

Advantages of hexadecimal

A

Why do people use hexadecimals to represent numbers stored in computers
Straightforward/easier to convert to binary as each hexadecimal digit is a nibble in binary
Shorter number to remember than binary
Quicker to enter
Less susceptible to errors
Easier to work with than binary

286
Q

Binary shifts

A

Shift to right of binary, if u convert to denary you’ll see it has been divided by 2
Shift to left, multiply by 2

287
Q

Character set

A

The range of characters (symbols, numbers, letters) that can be represented by a computer with each character having a binary value that computer understands/uses.

288
Q

What is used to represent characters

A

Binary
Each character is assigned a unique character code.
Each letter is converted to its character code (binary number)

289
Q

Character set examples

A

ASCII: 7 bits, 128 characters
Extended ASCII: 8 bits, 256, more characters it can represent and European symbols and other languages
Unicode: 16 bits or up to 32 bits. Encodes set characters. All languages

290
Q

What does ASCII stand for?

A

American Standard Code for Information Interchange
7 bit character system
codes character set computer uses
uses code to represent characters, symbols, numbers

291
Q

Why would Unicode be used

A

To use other special characters found in different languages

292
Q

A image is made up of

A

pixels which are the smallest element in a image and have a binary value to them which represents a colour
The binary numbers are stored in order in the file

293
Q

Bitmap image

A

Based on pixels
Each have binary value
That represents a colour

294
Q

Vector image

A

Based on mathematical algorithms

295
Q

Colour depth

A

Amounts of bits stored per pixel
How many colours that can be represented
The bigger the colour depth=The higher the accuracy, more colours can be represented.
But higher file size

296
Q

Resolution

A

Dimensions of image

Number of pixels per inch of screen

297
Q

Increasing resolution

A

Only increases quality if screen is bigger
Smaller images on big screens, image is stretched and lowers quality
Otherwise, increasing resolution= decreases battery life
/larger file size as more pixels-more data needed to be stored

298
Q

How does reducing the number of colours in a image can reduce its file size

A

Colour depth decrease
Fewer bits needed per colours
As less colours are represented
Which means fewer bits per pixel
Opposite: more colours, more bits required for each pixel
E.g two bits per pixel (00 to 11) - four possible colours

299
Q

Meta data

A

Background information (data) of a file
Why is metadata included in a file?
A computer needs to know the size of the image in terms of height, width, and colour depth in bits per pixel (bpp)
Allows the computer to recreate the image from binary

300
Q

How sound is sampled and stored in digital form

A

Amplitude of waveform measured. Converted into binary

At regular intervals

301
Q

Sample frequency

A

Number of samples taken per second

302
Q

Bit rate

A

Amount of data per second

Sample frequency x bit depth

303
Q

Bit depth for audio

A

Number of bits taken per sample

304
Q

Larger sample frequency and bit depth

A

Better quality
Higher file size
More bit depth- more sound/ data captured
More sample frequency- less time gap between each sample

Sound reproduced is closer to original

305
Q

The need for compression

A

The need for compression

  • Quicker upload/download/load/transfer time
  • Less storage space taken up
  • less mobile data/bandwidth usage
306
Q

Lossless compession

A 
Uses algorithm to compress file
No data is lost (data lost is only temporary, comes back when file is uncompressed) 
Reduces file size less than lossy
Better quality 
Suit for text and code as no data lost
307
Q

Lossy compression

A

Permanent loss of data
Cannot return to its original condition/not identical to original as data removed
Reduces file size more/significantly
Loss of quality more
Unlikely to be noticed by humans
For unnoticeable data / end users unlikely to notice the removal of data
E.g images, videos, sound
Where loss of quality is an acceptable trade off for smaller files
Cannot be used for text/code, makes unreadable /unable to execute code

308
Q

giveChange( money-price)

state how many parameters are passed into the giveChange() subrountine

A

1

309
Q

when recalling subroutines in flow charts, can use subroutine shape

A

e.g
vendItem()
giveChange(money-price)

310
Q

state what is meant by the term image resolution?

A

number of total pixels (in an image)

image height and image width (of an image)

311
Q

calculate the fewest number of bits that could be used to store the logo as a bitmap image. you must show your working

A

pixel width x pixel height x colour depth (bit per pixel)

312
Q

give two ways that the file size of a image could be reduced

A

reduce number of pixels/resolution
reduce number of colours
use lossy compression
use lossless compression

313
Q

opening, writing to and closing a file -pseudocode

A

file=
openWrite(“file name.txt”)
file.write(variable)
file.close()

314
Q

name=”Dru”

describe how a character set is used to represent the string value stored in the variable name

A

each character (in character set) has a unique (binary) number/value
each character in the string/is assigned its associated number/value
the binary value of each character is stored/.combined (in order)
by example e.g/ The binary value for D, then for r, then for u
Uses ASCII/Extended ASCII/Unicode

315
Q

when to use a Real

A

Returned value may not be a whole number/may have a decimal point in

316
Q

give reasons why computer scientists se hexademical to represent numbers instead of binary (mark scheme)

A

easier/quicker to communicate/enter/write/read/remember
less change of input errors/easier to spot errors
they are smaller/shorter
easy to convert between binary and hexadecimal

317
Q

modularising is

A

subroutines

A Level Computer Science (25 decks)

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