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A Level Computer Science > Paper 2 Revision Document 2 > Flashcards

Paper 2 Revision Document 2 Flashcards

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1
Q

Counting Numbers
Measure Numbers

A

Counting = Natural
Measure = Real

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2
Q

Advantages of Hexadecimal

A
  • easier to code
  • easier to read
  • easier to spot errors
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3
Q

Bit

A

The fundamental unit of information

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4
Q

Units (Kibi)

A

Kibi (Ki) = 2^10
Mebi (Mi) = 2^20
Gibi (Gi) = 2^30
Tebi (Ti) = 2^40

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5
Q

Absolute Error

A

original - binary

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6
Q

Relative Error

A

absolute error / original

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7
Q

Percentage Error

A

Relative error %

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8
Q

Character Sets (2)

A
  • a unique binary representation of a character
  • globally recognised, uniform
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9
Q

Advantages of Parity Bits (3)

A
  • little storage
  • less to process
  • easy to make
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10
Q

Disadvantages of Parity Bits (3)

A
  • multiple errors
  • doesn’t fix errors
  • not very reliable
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11
Q

Majority Voting (2)

A
  • bits can change due to interference
  • each bit transmitted 3 times - most common taken
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12
Q

Majority Voting Advantages (4)

A
  • multiple errors
  • fixes errors
  • easier to make
  • very reliable
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13
Q

Majority Voting Disadvantages (2)

A
  • more storage
  • more to process
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14
Q

Check Sums (3)

A
  • bytes of data lock added up
  • result transmitted with data
  • accepted if checksum = result
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15
Q

Check Digit (4)

A
  • many different algorithms
  • calculated from digits in the code
  • added to the end, then compared
  • purpose = spot human error on data entry
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16
Q

Analog

A

continuous stream of transmission

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17
Q

Digital

A

discrete, set of fixed values

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18
Q

Bitmap Graphics (2)

A
  • pixels, colour code –> binary, stored in grid like pattern
  • resolution = dots per inch
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19
Q

Bitmap Advantages (1)

A
  • real life
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20
Q

Bitmap Disadvantages (3)

A
  • big file size
  • not scalable
  • can’t edit easily
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21
Q

Vector Images (2)

A
  • objects layered + properties recorded
  • logos
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22
Q

Vector Images Advantages (4)

A
  • better quality
  • small file size
  • edit easily
  • scalable
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23
Q

Vector Images Disadvantages (1)

A
  • can’t represent real life images
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24
Q

Sample rate

A

num samples taken per second

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25
Q

Sample resolution (bit depth)

A

num bits available for each sample

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26
Q

Nyquist Theorem

A

accurate reading = sample res. >/ 2 x highest frequency

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27
Q

MIDI (8)

A
  • technical standard
  • describes: a protocol, digital interface, standard set of connectors
  • allows communication between computer + instruments to synthesise sound
  • controller send + receive event messages:
    • pitch, vibrato, note length
    • all easily changed
  • “List of Instructions”
  • sounds pre recorded from real instruments
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28
Q

MDI Advantages (4)

A
  • easy to modify
  • score generated directly from file
  • takes up much less storage
  • easy to change instruments
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29
Q

Run Length Encoding (3)

A
  • lossless compression
  • doc searched for repeated patterns
  • stores 1 instance + amount of times repeated
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30
Q

Dictionary Encoding (4)

A
  • lossless compression
  • doc searched word by word
  • 1st instance of word stored with unique reference
  • doc replaced with unique references
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31
Q

Caesar Cipher (1)

A
  • shift right n places
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32
Q

Caesar Cipher Advantages (2)

A
  • easy to code
  • simplistic
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33
Q

Caesar Cipher Disadvantages (3)

A
  • easy to hack
  • 25 possibilities
  • less secure
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34
Q

Vernam Cipher (4)

A
  • Plaintext XOR key = cipher key
  • Cipher key XOR key = plaintext
  • key must be: same length as plaintext, random, used once, secure
  • mathematically impossible to hack
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35
Q

Hardware

A

physical components of a computer

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36
Q

Software

A

code that carries out operations on hardware

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37
Q

Application Software (3)

A
  • created for specific purpose for user to carry out a task
  • e.g. spreadsheets, games, browsers
  • bespoke = tailor made for 1 user
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38
Q

System Software (2)

A
  • controls how computer works, tells it what to do
  • e.g. OS, utilities, translators, libraries
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39
Q

OS - Purpose

A

controls + organises the general operation of computer

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40
Q

OS - Functions (7)

A
  • managing the processor (alternate between simultaneous tasks)
  • managing the memory
  • handling external peripherals
  • platform for networking
  • security
  • user interface
  • utility programs
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41
Q

Defragmentation Software (2)

A
  • over time files on hard drives become split up making retrieval slower
  • helps consolidate parts back together
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42
Q

Assembly Language (1)

A
  • mnemonics have a 1-1 relationship with machine code
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43
Q

Low Level Languages (2)

A
  • each function maps directly to process in object code
  • closer to the hardware
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44
Q

Imperative High-Level Languages (1)

A

use sequence, selection and iteration where instructions must be executed in order

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45
Q

D-Type Flip Flop (3)

A
  • designed to store single bit of information
  • 2 inputs: clock input, clock signal
  • output only changes when clock pulse at rising edge
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46
Q

Computer Misuse Act (3)

A

Protects against
- unauthorised access
- with intent to commit crime
- with intent to modify or delete

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47
Q

Data Protection Act (8)

A

All data must be:
- Fairly and lawfully processed
- Processed for limited purposes
- Adequate, relevant and not excessive
- Accurate and up to date
- Not kept longer than necessary
- Processed in line with your rights
- Secure
- Not transferred to other countries without adequate protection

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48
Q

Acts (7)

A
  • Computer Misuse Act
  • Data Protection Act
  • Freedom of Information Act
  • Copyright, Designs and Patents Act
  • Creative Commons Licensing
  • The Regulation of Investigatory Powers Act
  • Health and Safety
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49
Q

Main Memory (RAM) (4)

A
  • primary storage - volatile
  • used for quick and direct access
  • data can only be manipulated if stored here
  • OS, software application, info for CPU
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50
Q

Busses

A

Pass data around different parts of the computer

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51
Q

Address Bus

A

identify locations in memory

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52
Q

Data Bus

A

pass data/instructions around computer

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53
Q

Control Bus

A

communication between CPU and devices in computer

54
Q

I/O Controllers (2)

A
  • may pass errors messages/deal with interrupts
  • contain a kernel (pass info between 2 areas)
55
Q

Von Neumann Architecture (5)

A
  • 1 memory location
  • easy access from ALU to I/O
  • can code with complex/changing programs
  • general purpose computing systems
  • access to memory from all parts of system
56
Q

Harvard Architecture (5)

A
  • 2 memory locations
  • can access data & instructions simultaneously
  • reduces bottle neck
  • can have different bus widths (saves £)
  • embedded systems
57
Q

The Stored Program Concept

A

Machine code instructions stored in main memory are fetched and executed serially by a processor that performs arithmetic and logical operations

58
Q

Registers

A

Store single items of data within the CPU

59
Q

MAR

A

stores address of where to store/retrieve data

60
Q

MBR

A

stores data/instructions that have been retrieved or to be stored

61
Q

CIR

A

holds current instruction after decoded

62
Q

PC

A

holds count of instruction next to be executed

63
Q

Accumulator

A

holds result of ALU calculations

64
Q

The Processor Instruction Set (2)

A
  • complete set of all instructions in machine code that can be recognised & executed by a CPU
  • processor specific
65
Q

Fetch-Execute Cycle: Fetch (6)

A
  • PC copied to MAR
  • MAR copied & sent: address bus
  • CU sends signal to read: control bus
  • data copied & sent to MBR: data bus
  • MBR copied to CIR
  • PC incremented by 1
66
Q

Fetch-Execute Cycle: Decode (4)

A
  • instruction split: opcode/operand
  • CU decodes data
  • Opcode –> CIR
  • Value –> ACC or Address –> MAR
67
Q

Fetch-Execute Cycle: Execute (3)

A
  • data fetched/stored if necessary
  • ALU performs calculations
  • result stored or outputted
68
Q

Addressing Modes

A

Immediate: operand = data (#)
Direct: operand = address (R)

69
Q

Factors Affecting Processor Performance (6)

A

Cache
- Frequently used instructions
- Faster than RAM (inside CPU)
Clock speed (per second)
Cores (simultaneously)
RAM (no reliance on virtual memory)
Bus Width (send whole instructions)
Word Length

70
Q

Barcode Reader (3)

A
  • Laser hits barcode
  • Reflected by white, absorbed by black
  • Hits sensor → converted to binary
71
Q

Digital Camera (3)

A
  • Lens focuses light onto a sensor
  • Frequency = colour
  • Sensor is a grid - each part had colour recorded (stored in binary grid)
72
Q

Laser Printer (4)

A
  • Electron beam at -ve drum to create +ve charges pattern
  • Drum picks up ink on +ve charges
  • Ink → paper (colours layer)
  • Heat press
73
Q

RFID Reader (4)

A
  • Reader transmits data via radio waves
  • Energy activates chip, which modulates energy
  • Signal transmitted back to read
  • Stored and/or compared to database
74
Q

Secondary Storage (2)

A
  • hard disk not immediately accessible by processor
  • needed once RAM is full
75
Q

Optical (4)

A
  • Pits and peaks = 1s and 0s
  • Time taken for laser to reflect back
  • Short = peak = 1, long = pit = 0
  • Pits and peaks in spirals
76
Q

Optical (Adv) (2)

A
  • small
  • very reliable
77
Q

Optical (Dis) (2)

A
  • easily scratched
  • can’t be edited
78
Q

Magnetic (3)

A
  • Positive/negative charges = 1s and 0s
  • Write: head charges tape (e.m. charge)
  • Read: head attracted (0) /repelled (1)
79
Q

Magnetic (Adv) (3)

A
  • fast read/write speed
  • large capacity
  • reliable
80
Q

Magnetic (Dis) (2)

A
  • moving parts (corruptible)
  • expensive
81
Q

Flash (3)

A
  • Non-volatile
  • Uses electrical effects to store data
  • No moving parts
82
Q

Flash (Adv) (3)

A
  • reliable
  • fast
  • compact
83
Q

Flash (Dis) (1)

A
  • wears out over time
84
Q

Baud Rate

A

rate at which data can be transmitted (signal units)

85
Q

Bit Rate

A

rate at which bits are transferred (bit rate >/ baud rate)

86
Q

Latency

A

the delay between transfer of data and result of that instruction

87
Q

Protocol

A

set of rules for data exchange between devices

88
Q

Methods of Transmission: Serial (2)

A
  • 1 wire (1 bit at a time)
  • external distances
89
Q

Methods of Transmission: Serial (Adv) (3)

A
  • simple
  • cheap
  • reliable
90
Q

Methods of Transmission: Serial (Dis) (1)

A
  • slow transmission
91
Q

Methods of Transmission: Parallel (2)

A
  • multiple wires
  • internal distances
92
Q

Methods of Transmission: Parallel (Adv) (1)

A
  • faster transmission
93
Q

Methods of Transmission: Parallel (Dis) (2)

A
  • less reliable (skew due to interference)
  • more expensive
94
Q

Types of Transmission: Synchronous (3)

A
  • Data sent at regular intervals
  • Synchronised by clock pulse shared between sender & receiver
  • Real time sensitive data
95
Q

Types of Transmission: Asynchronous (3)

A
  • Each byte sent separately
  • Bytes sent as soon as they’re ready
  • Parity, start & stop
96
Q

Start and Stop Bits (defs)

A

Start = notifies receiver that data is being sent
Stop = notifies receiver that end of data has been sent

97
Q

Bus Topology (2)

A
  • One cable called the backbone
  • Terminator at end of cable that reflects signals
98
Q

Bus Topology (Adv) (2)

A
  • cheaper to install
  • no additional hardware
99
Q

Bus Topology (Dis) (3)

A
  • poor security (all computers on network can see transmission)
  • main cable fail
  • performance decreases with traffic
100
Q

Star Topology (1)

A
  • connects to switch or hub
101
Q

Star Topology (Adv) (5)

A
  • easy to add
  • handle high traffic
  • more secure
  • easy to isolate faults
  • no collisions
102
Q

Star Topology (Dis) (2)

A
  • central node goes down
  • £ set up
103
Q

Client-Server Network (1)

A
  • Dedicated server - allocated to specific computers
104
Q

Peer-to-Peer Network (2)

A
  • All devices have equal status
  • No specialised hardware needed
105
Q

WiFi (2)

A
  • WiFi is a wireless LAN based on international standards
  • Hot spots = public WiFi
106
Q

NIC (3)

A
  • Located in device
  • Allows device to connect to wireless system
  • Assigns MAC address
107
Q

WAP (3)

A
  • Located in router
  • Allows wireless devices to connect to wired network
  • Assigns IP address
108
Q

Network Security (4)

A
  • Doesn’t stop allowed user from using malware
  • WPA/WPA2 -WiFi Protected Access
    • Authentication, encryption, passwords
  • SSID - Service Set Identifier
    • Unique number to identify a network
  • MAC Address white list
109
Q

Firewalls (5)

A
  • A system that filters network traffic to protect against unauthorised flows of data in/out of a network
  • Hardware or software
  • Isolates network traffic
  • allows/denies based on IP address
  • Stateful packet inspection & packet filtering
110
Q

Proxy Servers (4)

A
  • Client ←→ Proxy Server ←→ Web Server
  • Data obtained from web server, then stored on Proxy Server
  • Speeds up data access,
  • More security (IP address hidden from web server)
111
Q

Malware

A

Software created with intention to cause harm

112
Q

Viruses (3)

A
  • Attaches to file enabling it to spread from one device to another
  • Typically executable file
  • Needs to be opened
113
Q

Worms (4)

A
  • Similar to viruses
  • No need for human interaction
  • Automatically self replicates
  • Spread through lack of awareness
114
Q

Trojans (3)

A
  • Appears genuine, has hidden agenda
  • Creates backdoors which malicious users can exploit
  • Doesn’t self-replicate, spread or cause harm
115
Q

Asymmetric Encryption (keys)

A
  • public key = encrypt
  • private key = decrypt
116
Q

Digital Certificates (3)

A
  • Unique code assigned by a business to verify your identity
  • Contains name, ID, public key, signature
  • From a certification authority
117
Q

Digital Signatures (2)

A
  • Similar to real life signature
  • Uses mathematical functions + keys to create unique signature
118
Q

Primary Key

A

unique identifier for each row

119
Q

Composite

A

primary key contains more than 1 field to make a unique value

120
Q

Entity
Record
Attribute

A

table
row
field

121
Q

Normalisation (def)

A

Process of storing data while removing redundant data & eliminating data duplication

122
Q

Normalisation Provides Rules that Help (3)

A
  • Organise data efficiently
  • Eliminate redundant data
  • Ensures only related data stored in table
123
Q

1NF (4)

A
  • No columns with repeated/similar data
  • Each data item is atomic
  • Each row has a primary key (unique)
  • Each field has a unique name
124
Q

2NF (1)

A

non-key attributes must depend on every part of the primary key

125
Q

3NF (1)

A

no non-key attributes that depend on another non-key attribute

126
Q

Benefits of Normalisation (3)

A
  • Smaller database = less £ on storage
  • Less search data = faster query
  • No duplication = less risk of mistakes
127
Q

Problems with Normalisation (2)

A
  • more tables = slower
  • more tables = more complex queries
128
Q

INSERT

A

INSERT INTO table (field1, field2) VALUES (value1, value2);

129
Q

UPDATE

A

UPDATE table SET fieldToChange = newFieldValue WHERE condition;

130
Q

DELETE

A

DELETE FROM table WHERE condition;

131
Q

CREATE TABLE

A

CREATE TABLE tableName(
ID INTEGER NOT NULL PRIMARY KEY,
field1 VARCHAR (50),
field2 DATE/TIME)

A Level Computer Science (10 decks)

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