Paper 2 Revision Document 2 Flashcards
Counting Numbers
Measure Numbers
Counting = Natural
Measure = Real
Advantages of Hexadecimal
- easier to code
- easier to read
- easier to spot errors
Bit
The fundamental unit of information
Units (Kibi)
Kibi (Ki) = 2^10
Mebi (Mi) = 2^20
Gibi (Gi) = 2^30
Tebi (Ti) = 2^40
Absolute Error
original - binary
Relative Error
absolute error / original
Percentage Error
Relative error %
Character Sets (2)
- a unique binary representation of a character
- globally recognised, uniform
Advantages of Parity Bits (3)
- little storage
- less to process
- easy to make
Disadvantages of Parity Bits (3)
- multiple errors
- doesn’t fix errors
- not very reliable
Majority Voting (2)
- bits can change due to interference
- each bit transmitted 3 times - most common taken
Majority Voting Advantages (4)
- multiple errors
- fixes errors
- easier to make
- very reliable
Majority Voting Disadvantages (2)
- more storage
- more to process
Check Sums (3)
- bytes of data lock added up
- result transmitted with data
- accepted if checksum = result
Check Digit (4)
- many different algorithms
- calculated from digits in the code
- added to the end, then compared
- purpose = spot human error on data entry
Analog
continuous stream of transmission
Digital
discrete, set of fixed values
Bitmap Graphics (2)
- pixels, colour code –> binary, stored in grid like pattern
- resolution = dots per inch
Bitmap Advantages (1)
- real life
Bitmap Disadvantages (3)
- big file size
- not scalable
- can’t edit easily
Vector Images (2)
- objects layered + properties recorded
- logos
Vector Images Advantages (4)
- better quality
- small file size
- edit easily
- scalable
Vector Images Disadvantages (1)
- can’t represent real life images
Sample rate
num samples taken per second
Sample resolution (bit depth)
num bits available for each sample
Nyquist Theorem
accurate reading = sample res. >/ 2 x highest frequency
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
MDI Advantages (4)
- easy to modify
- score generated directly from file
- takes up much less storage
- easy to change instruments
Run Length Encoding (3)
- lossless compression
- doc searched for repeated patterns
- stores 1 instance + amount of times repeated
Dictionary Encoding (4)
- lossless compression
- doc searched word by word
- 1st instance of word stored with unique reference
- doc replaced with unique references
Caesar Cipher (1)
- shift right n places
Caesar Cipher Advantages (2)
- easy to code
- simplistic
Caesar Cipher Disadvantages (3)
- easy to hack
- 25 possibilities
- less secure
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
Hardware
physical components of a computer
Software
code that carries out operations on hardware
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
System Software (2)
- controls how computer works, tells it what to do
- e.g. OS, utilities, translators, libraries
OS - Purpose
controls + organises the general operation of computer
OS - Functions (7)
- managing the processor (alternate between simultaneous tasks)
- managing the memory
- handling external peripherals
- platform for networking
- security
- user interface
- utility programs
Defragmentation Software (2)
- over time files on hard drives become split up making retrieval slower
- helps consolidate parts back together
Assembly Language (1)
- mnemonics have a 1-1 relationship with machine code
Low Level Languages (2)
- each function maps directly to process in object code
- closer to the hardware
Imperative High-Level Languages (1)
use sequence, selection and iteration where instructions must be executed in order
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
Computer Misuse Act (3)
Protects against
- unauthorised access
- with intent to commit crime
- with intent to modify or delete
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
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
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
Busses
Pass data around different parts of the computer
Address Bus
identify locations in memory
Data Bus
pass data/instructions around computer
Control Bus
communication between CPU and devices in computer
I/O Controllers (2)
- may pass errors messages/deal with interrupts
- contain a kernel (pass info between 2 areas)
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
Harvard Architecture (5)
- 2 memory locations
- can access data & instructions simultaneously
- reduces bottle neck
- can have different bus widths (saves £)
- embedded systems
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
Registers
Store single items of data within the CPU
MAR
stores address of where to store/retrieve data
MBR
stores data/instructions that have been retrieved or to be stored
CIR
holds current instruction after decoded
PC
holds count of instruction next to be executed
Accumulator
holds result of ALU calculations
The Processor Instruction Set (2)
- complete set of all instructions in machine code that can be recognised & executed by a CPU
- processor specific
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
Fetch-Execute Cycle: Decode (4)
- instruction split: opcode/operand
- CU decodes data
- Opcode –> CIR
- Value –> ACC or Address –> MAR
Fetch-Execute Cycle: Execute (3)
- data fetched/stored if necessary
- ALU performs calculations
- result stored or outputted
Addressing Modes
Immediate: operand = data (#)
Direct: operand = address (R)
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
Barcode Reader (3)
- Laser hits barcode
- Reflected by white, absorbed by black
- Hits sensor → converted to binary
Digital Camera (3)
- Lens focuses light onto a sensor
- Frequency = colour
- Sensor is a grid - each part had colour recorded (stored in binary grid)
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
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
Secondary Storage (2)
- hard disk not immediately accessible by processor
- needed once RAM is full
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
Optical (Adv) (2)
- small
- very reliable
Optical (Dis) (2)
- easily scratched
- can’t be edited
Magnetic (3)
- Positive/negative charges = 1s and 0s
- Write: head charges tape (e.m. charge)
- Read: head attracted (0) /repelled (1)
Magnetic (Adv) (3)
- fast read/write speed
- large capacity
- reliable
Magnetic (Dis) (2)
- moving parts (corruptible)
- expensive
Flash (3)
- Non-volatile
- Uses electrical effects to store data
- No moving parts
Flash (Adv) (3)
- reliable
- fast
- compact
Flash (Dis) (1)
- wears out over time
Baud Rate
rate at which data can be transmitted (signal units)
Bit Rate
rate at which bits are transferred (bit rate >/ baud rate)
Latency
the delay between transfer of data and result of that instruction
Protocol
set of rules for data exchange between devices
Methods of Transmission: Serial (2)
- 1 wire (1 bit at a time)
- external distances
Methods of Transmission: Serial (Adv) (3)
- simple
- cheap
- reliable
Methods of Transmission: Serial (Dis) (1)
- slow transmission
Methods of Transmission: Parallel (2)
- multiple wires
- internal distances
Methods of Transmission: Parallel (Adv) (1)
- faster transmission
Methods of Transmission: Parallel (Dis) (2)
- less reliable (skew due to interference)
- more expensive
Types of Transmission: Synchronous (3)
- Data sent at regular intervals
- Synchronised by clock pulse shared between sender & receiver
- Real time sensitive data
Types of Transmission: Asynchronous (3)
- Each byte sent separately
- Bytes sent as soon as they’re ready
- Parity, start & stop
Start and Stop Bits (defs)
Start = notifies receiver that data is being sent
Stop = notifies receiver that end of data has been sent
Bus Topology (2)
- One cable called the backbone
- Terminator at end of cable that reflects signals
Bus Topology (Adv) (2)
- cheaper to install
- no additional hardware
Bus Topology (Dis) (3)
- poor security (all computers on network can see transmission)
- main cable fail
- performance decreases with traffic
Star Topology (1)
- connects to switch or hub
Star Topology (Adv) (5)
- easy to add
- handle high traffic
- more secure
- easy to isolate faults
- no collisions
Star Topology (Dis) (2)
- central node goes down
- £ set up
Client-Server Network (1)
- Dedicated server - allocated to specific computers
Peer-to-Peer Network (2)
- All devices have equal status
- No specialised hardware needed
WiFi (2)
- WiFi is a wireless LAN based on international standards
- Hot spots = public WiFi
NIC (3)
- Located in device
- Allows device to connect to wireless system
- Assigns MAC address
WAP (3)
- Located in router
- Allows wireless devices to connect to wired network
- Assigns IP address
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
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
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)
Malware
Software created with intention to cause harm
Viruses (3)
- Attaches to file enabling it to spread from one device to another
- Typically executable file
- Needs to be opened
Worms (4)
- Similar to viruses
- No need for human interaction
- Automatically self replicates
- Spread through lack of awareness
Trojans (3)
- Appears genuine, has hidden agenda
- Creates backdoors which malicious users can exploit
- Doesn’t self-replicate, spread or cause harm
Asymmetric Encryption (keys)
- public key = encrypt
- private key = decrypt
Digital Certificates (3)
- Unique code assigned by a business to verify your identity
- Contains name, ID, public key, signature
- From a certification authority
Digital Signatures (2)
- Similar to real life signature
- Uses mathematical functions + keys to create unique signature
Primary Key
unique identifier for each row
Composite
primary key contains more than 1 field to make a unique value
Entity
Record
Attribute
table
row
field
Normalisation (def)
Process of storing data while removing redundant data & eliminating data duplication
Normalisation Provides Rules that Help (3)
- Organise data efficiently
- Eliminate redundant data
- Ensures only related data stored in table
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
2NF (1)
non-key attributes must depend on every part of the primary key
3NF (1)
no non-key attributes that depend on another non-key attribute
Benefits of Normalisation (3)
- Smaller database = less £ on storage
- Less search data = faster query
- No duplication = less risk of mistakes
Problems with Normalisation (2)
- more tables = slower
- more tables = more complex queries
INSERT
INSERT INTO table (field1, field2) VALUES (value1, value2);
UPDATE
UPDATE table SET fieldToChange = newFieldValue WHERE condition;
DELETE
DELETE FROM table WHERE condition;
CREATE TABLE
CREATE TABLE tableName(
ID INTEGER NOT NULL PRIMARY KEY,
field1 VARCHAR (50),
field2 DATE/TIME)
