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
Sample resolution (bit depth)
num bits available for each sample
26
Nyquist Theorem
accurate reading = sample res. >/ 2 x highest frequency
27
MIDI (8)
- 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
28
MDI Advantages (4)
- easy to modify - score generated directly from file - takes up much less storage - easy to change instruments
29
Run Length Encoding (3)
- lossless compression - doc searched for repeated patterns - stores 1 instance + amount of times repeated
30
Dictionary Encoding (4)
- lossless compression - doc searched word by word - 1st instance of word stored with unique reference - doc replaced with unique references
31
Caesar Cipher (1)
- shift right n places
32
Caesar Cipher Advantages (2)
- easy to code - simplistic
33
Caesar Cipher Disadvantages (3)
- easy to hack - 25 possibilities - less secure
34
Vernam Cipher (4)
- 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
35
Hardware
physical components of a computer
36
Software
code that carries out operations on hardware
37
Application Software (3)
- created for specific purpose for user to carry out a task - e.g. spreadsheets, games, browsers - bespoke = tailor made for 1 user
38
System Software (2)
- controls how computer works, tells it what to do - e.g. OS, utilities, translators, libraries
39
OS - Purpose
controls + organises the general operation of computer
40
OS - Functions (7)
- managing the processor (alternate between simultaneous tasks) - managing the memory - handling external peripherals - platform for networking - security - user interface - utility programs
41
Defragmentation Software (2)
- over time files on hard drives become split up making retrieval slower - helps consolidate parts back together
42
Assembly Language (1)
- mnemonics have a 1-1 relationship with machine code
43
Low Level Languages (2)
- each function maps directly to process in object code - closer to the hardware
44
Imperative High-Level Languages (1)
use sequence, selection and iteration where instructions must be executed in order
45
D-Type Flip Flop (3)
- designed to store single bit of information - 2 inputs: clock input, clock signal - output only changes when clock pulse at rising edge
46
Computer Misuse Act (3)
Protects against - unauthorised access - with intent to commit crime - with intent to modify or delete
47
Data Protection Act (8)
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
48
Acts (7)
- 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
49
Main Memory (RAM) (4)
- primary storage - volatile - used for quick and direct access - data can only be manipulated if stored here - OS, software application, info for CPU
50
Busses
Pass data around different parts of the computer
51
Address Bus
identify locations in memory
52
Data Bus
pass data/instructions around computer
53
Control Bus
communication between CPU and devices in computer
54
I/O Controllers (2)
- may pass errors messages/deal with interrupts - contain a kernel (pass info between 2 areas)
55
Von Neumann Architecture (5)
- 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
Harvard Architecture (5)
- 2 memory locations - can access data & instructions simultaneously - reduces bottle neck - can have different bus widths (saves £) - embedded systems
57
The Stored Program Concept
Machine code instructions stored in main memory are fetched and executed serially by a processor that performs arithmetic and logical operations
58
Registers
Store single items of data within the CPU
59
MAR
stores address of where to store/retrieve data
60
MBR
stores data/instructions that have been retrieved or to be stored
61
CIR
holds current instruction after decoded
62
PC
holds count of instruction next to be executed
63
Accumulator
holds result of ALU calculations
64
The Processor Instruction Set (2)
- complete set of all instructions in machine code that can be recognised & executed by a CPU - processor specific
65
Fetch-Execute Cycle: Fetch (6)
- 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
Fetch-Execute Cycle: Decode (4)
- instruction split: opcode/operand - CU decodes data - Opcode --> CIR - Value --> ACC or Address --> MAR
67
Fetch-Execute Cycle: Execute (3)
- data fetched/stored if necessary - ALU performs calculations - result stored or outputted
68
Addressing Modes
Immediate: operand = data (#) Direct: operand = address (R)
69
Factors Affecting Processor Performance (6)
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
Barcode Reader (3)
- Laser hits barcode - Reflected by white, absorbed by black - Hits sensor → converted to binary
71
Digital Camera (3)
- Lens focuses light onto a sensor - Frequency = colour - Sensor is a grid - each part had colour recorded (stored in binary grid)
72
Laser Printer (4)
- Electron beam at -ve drum to create +ve charges pattern - Drum picks up ink on +ve charges - Ink → paper (colours layer) - Heat press
73
RFID Reader (4)
- Reader transmits data via radio waves - Energy activates chip, which modulates energy - Signal transmitted back to read - Stored and/or compared to database
74
Secondary Storage (2)
- hard disk not immediately accessible by processor - needed once RAM is full
75
Optical (4)
- 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
Optical (Adv) (2)
- small - very reliable
77
Optical (Dis) (2)
- easily scratched - can't be edited
78
Magnetic (3)
- Positive/negative charges = 1s and 0s - Write: head charges tape (e.m. charge) - Read: head attracted (0) /repelled (1)
79
Magnetic (Adv) (3)
- fast read/write speed - large capacity - reliable
80
Magnetic (Dis) (2)
- moving parts (corruptible) - expensive
81
Flash (3)
- Non-volatile - Uses electrical effects to store data - No moving parts
82
Flash (Adv) (3)
- reliable - fast - compact
83
Flash (Dis) (1)
- wears out over time
84
Baud Rate
rate at which data can be transmitted (signal units)
85
Bit Rate
rate at which bits are transferred (bit rate >/ baud rate)
86
Latency
the delay between transfer of data and result of that instruction
87
Protocol
set of rules for data exchange between devices
88
Methods of Transmission: Serial (2)
- 1 wire (1 bit at a time) - external distances
89
Methods of Transmission: Serial (Adv) (3)
- simple - cheap - reliable
90
Methods of Transmission: Serial (Dis) (1)
- slow transmission
91
Methods of Transmission: Parallel (2)
- multiple wires - internal distances
92
Methods of Transmission: Parallel (Adv) (1)
- faster transmission
93
Methods of Transmission: Parallel (Dis) (2)
- less reliable (skew due to interference) - more expensive
94
Types of Transmission: Synchronous (3)
- Data sent at regular intervals - Synchronised by clock pulse shared between sender & receiver - Real time sensitive data
95
Types of Transmission: Asynchronous (3)
- Each byte sent separately - Bytes sent as soon as they’re ready - Parity, start & stop
96
Start and Stop Bits (defs)
Start = notifies receiver that data is being sent Stop = notifies receiver that end of data has been sent
97
Bus Topology (2)
- One cable called the backbone - Terminator at end of cable that reflects signals
98
Bus Topology (Adv) (2)
- cheaper to install - no additional hardware
99
Bus Topology (Dis) (3)
- poor security (all computers on network can see transmission) - main cable fail - performance decreases with traffic
100
Star Topology (1)
- connects to switch or hub
101
Star Topology (Adv) (5)
- easy to add - handle high traffic - more secure - easy to isolate faults - no collisions
102
Star Topology (Dis) (2)
- central node goes down - £ set up
103
Client-Server Network (1)
- Dedicated server - allocated to specific computers
104
Peer-to-Peer Network (2)
- All devices have equal status - No specialised hardware needed
105
WiFi (2)
- WiFi is a wireless LAN based on international standards - Hot spots = public WiFi
106
NIC (3)
- Located in device - Allows device to connect to wireless system - Assigns MAC address
107
WAP (3)
- Located in router - Allows wireless devices to connect to wired network - Assigns IP address
108
Network Security (4)
- 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
Firewalls (5)
- 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
Proxy Servers (4)
- 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
Malware
Software created with intention to cause harm
112
Viruses (3)
- Attaches to file enabling it to spread from one device to another - Typically executable file - Needs to be opened
113
Worms (4)
- Similar to viruses - No need for human interaction - Automatically self replicates - Spread through lack of awareness
114
Trojans (3)
- Appears genuine, has hidden agenda - Creates backdoors which malicious users can exploit - Doesn’t self-replicate, spread or cause harm
115
Asymmetric Encryption (keys)
- public key = encrypt - private key = decrypt
116
Digital Certificates (3)
- Unique code assigned by a business to verify your identity - Contains name, ID, public key, signature - From a certification authority
117
Digital Signatures (2)
- Similar to real life signature - Uses mathematical functions + keys to create unique signature
118
Primary Key
unique identifier for each row
119
Composite
primary key contains more than 1 field to make a unique value
120
Entity Record Attribute
table row field
121
Normalisation (def)
Process of storing data while removing redundant data & eliminating data duplication
122
Normalisation Provides Rules that Help (3)
- Organise data efficiently - Eliminate redundant data - Ensures only related data stored in table
123
1NF (4)
- 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
2NF (1)
non-key attributes must depend on every part of the primary key
125
3NF (1)
no non-key attributes that depend on another non-key attribute
126
Benefits of Normalisation (3)
- Smaller database = less £ on storage - Less search data = faster query - No duplication = less risk of mistakes
127
Problems with Normalisation (2)
- more tables = slower - more tables = more complex queries
128
INSERT
INSERT INTO table (field1, field2) VALUES (value1, value2);
129
UPDATE
UPDATE table SET fieldToChange = newFieldValue WHERE condition;
130
DELETE
DELETE FROM table WHERE condition;
131
CREATE TABLE
CREATE TABLE tableName( ID INTEGER NOT NULL PRIMARY KEY, field1 VARCHAR (50), field2 DATE/TIME)
A Level Computer Science
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