Paper 1
Last minute exam notes to go through before sitting the Paper 1 exam.
Lossy Compression
Compression algorithm is used
Original file cannot be restored
Deletes unnecessary data from the file
Removes sounds that cannot be heard by the human ear
Reduces video quality
Reduces the sample rate & resolution
For more details on compression, visit here.
Lossless Compression
Compression algorithm is used
Original file can be restored
RLE & Huffman encoding is used
Repeated patterns are identified & indexed
For more details on compression, visit here.
Packet Switching
A message is split up into data packets
These packets are labelled with their headers and trailers
Then sent into the internet
Routers will route every packet based on their header
The routing selection depends on the number of packets at each node
Each packet will travel as fast as it can to the destination
Packets re-sorted into the correct order based on their trailer
For more information, look here.
CRC's
Sender adds up the 1-bits and stores as a hexadecimal number in the trailer
When it arrives, receiver recalculates the 1-bits
This value is checked against the value in the trailer
If both match, then no error has occurred
If they do not match, then the packet is resent
View more details here.
USB's
Device automatically detected and driver loaded
Only fits one way (or backwards compatible)
Universal standard
Supports different or multiple data transmission rates
ARQ
It uses acknowledgement and timeout
When data is sent, a timer is started
If there are no errors, a positive acknowledgement is sent
If there is an error, a negative acknowledgement is sent and the data is re-sent
If no acknowledgement is sent, then the sender will wait for timeout
Then the data is re-sent again until an acknowledgment is received
Von Neumann Architecture
PC holds address of the instruction
Address sent to MAR via the address bus
MAR goes to memory where the instruction is stored
Instruction sent to MDR via the data bus
Instruction passed to CIR
CU sends signals to manage entire process via control bus
For a full detailed explanation on the individual components and part, revise here.
QR & Barcode Scanners
Device shines laser at the code
White reflects light and black absorbs light
Corners used to determine position or orientation (QR)
Device reads reflected light using sensors
Data converted to binary
Link is stored within the code (QR)
Keyboard
Membrane with circuit board is present at the base of the keys
When a key is pressed, this presses a switch
This completes a circuit
Location of each keypress is calculated
Index of characters is searched to find which key was pressed
Each character has a Unicode value which is converted into binary
Processed by the CPU to action each keypress
Operating System
Performs basic functions of a computer and manages the hardware
Provides the user a platform to run software and a user interface
Interrupts
Interrupt signal sent to the CPU or processor
CPU stops the task its currently doing to service the interrupt
Interrupt service routine is created to service the interrupt
Message is displayed to user to notify them
More details can be viewed here.
Interpreters & Compilers
Interpreter used while writing the program
Used to debug code line by line
Compiler used when the program is completed
Used to create an executable file
Revise it further here.
Web Pages / Browser
User types URL into the browser
Browser sends the URL to DNS using HTTP
DNS finds matching IP for that URL and sends to the browser
Browser sends a request to server for web pages
Web pages sent to browser
Browser renders HTML to display web pages
Security certificates exchanged
SSL or HTTPS is used to encrypt the data
Check your knowledge on structure and presentation of web pages here.
Firewalls
Monitors incoming and outgoing traffic
Checks that the traffic meets the rules set by the user
It will block any traffic that doesn’t meet the rules
User can create blacklist or whitelist of IP’s to block traffic from
Can close certain ports
Definitions
Character Sets All the characters and symbols that a computer can represent where each one is assigned a specific value
Sampling Resolution Also bit depth, the number of bits per sample#
Sampling Rate The number of sound samples taken per second (measured in Hz)
Colour Depth The number of bits used to represent each colour
Image Resolution The dimensions of an image ( pixels [width x height] )
Encryption Encoding data into a form that is not useful unless it is passed through an algorithm
Instruction Set List of commands that can be processed by a CPU
Embedded System A system with either one function only or a limited set of functions
Primary Storage Directly accessed by the CPU RAM, ROM, Cache
Secondary Storage Permanent storage which is not directly accessed by the CPU HDD, SSD, Optical Storage
Router Connects one network to another and analyses data packets
Utility Software Performs specific tasks and helps to configure a system
Low-level Language Language that sits close to a computer’s instruction set
IDE Integrated Development Environment Piece of software that is used to write and test software
URL Uniform Resource Locator Text based address that identifies the location of a resource on the internet
Blockchain Digital ledger that records all transactions and is decentralised
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