Paper 1 Principles of Computing

Paper 1 Principles of Computing

1. Binary

   • 2 states
     • Representing data
       • 1 bit = 2 possibilities
         • 2 bits = 2^2
           • 3 bits = 2^3
             • 4 bits = 2^4
               • 8 bits = 2^8 = 256 possibilities
       • Images
         • Colour depth = num of bits to store colour about 1 pixel
           • 8 bit colour depth = 256 colours
             • All images made up from Red, Green Blue
               • 24 bit colour depth = 8 bits for R, 8 for G, 8 for B
                 • = 255 x 255 x 255 shades PER PIXEL
         • Resolution
           • Pixels per inch
             • A pixel is the smallest unit of colour in an image
               • Resolution = width (pixels) x height (pixels)
                 • File size (bits) = resolution x colour depth
                   • bits to bytes Divide by 8
                     • Bytes to KB Divide by 1024
                       • KB to MB Divide by 1024 etc
       • Text
         • Uses character sets
           • ASCII
             • 7 bits
               • 128 characters
           • Unicode
             • 16 bits
               • 2^16 65536 characters
           • Extended ASCII set
             • 8 bits
               • 256 characters
       • Sound
         • Analogue to digital
           • Sampling
             • Take samples at regular intervals
               • Amplitude = height of wave. Higher = louder
           • Bit Depth
             • Num of bits to store data about each sample
         • File size in bits = samples per second x bit depth x duration in seconds x number of channels
   • Bit
     • Nibble = 4 bits
       • Byte = 8 bits
         • Kilobyte = 1024 bytes
           • Megabyte = 1024 KB
             • Gigabyte = 1024 MB
               • Terabyte = 1024 GB
   • Place values for 8 bits = 128, 64. 32, 16, 8, 4, 2,1
     • Maximum value stored in 8 bits is 255
       • Range of values in 8 bits is 0 to 255
         • Maximum number of combinations in 8 bits is 256
   • Storage
     • Compression
       • Removing data
         • Reduces file size
           • Speeds loading or file access
       • Lossy
         • Permanent data loss
           • Some loss of quality
             • Usually unnoticed by human eye or ear
         • JPEG - lossy image file type
         • MP3 - lossy audio file type
       • Lossless
         • Data compressed on saving, restored on re-opening
         • Run Length Encoding
           • Patterns or runs of the same data next to each other are coded in a different way, saving space
             • EG. A run of blue pixels in a photo containing sky
           • Not good for text as few repeated letters so file size may not get smaller & may even get bigger
         • PNG lossless image file type
         • FLAC lossless audio file type
     • Secondary storage
       • Magnetic hard disc drive
         • Magnets to represent the 2 states
       • Optical discs
         • CD
         • DVD
         • Bluray
         • Pits and lands burnt on the disc & read with a laser
         • Cheap
       • NAND flash/ solid state drives
         • use electron pools to represent the 2 states
         • Solid state hard drive
           • Internal
           • External
         • SD memory card
         • USB memory stick
       • Cloud Storage
         • Server farms
           • Accessed via the Internet
   • Binary maths
     • Addition
       • 1+1 = 0 carry 1
         • 1+1+1 = 1 carry 1
       • Overflow error
         • As a result of a sum, there aren't enough bits to hold the result
           • Program crashes
     • Multiplcation
       • Left logical shift
         • used with unsigned binary numbers
         • shift 1 place = multiply by 2
         • shift 2 place = multiply by 2^2
         • shift 3 places - multiply by 2^ 3
           • etc
     • Division
       • Right logical shift
         • shift 1 place = divide by 2
           • etc. as per multiplication
     • Signed numbers
       • Indicates if a binary number is +ve or -ve
         • left-most bit = Most Significant Bit (MSB)
           • If MSB = 1, the number is negative
             • If MSB is 0, the number is positive
       • Two's Complement
         • Most common method for showing -ve numbers in modern computers
         • To find the Two's Complement of a binary number:
           • Flip the bits, and add 1
         • Checking a Two's Complement number
           • Add the Two's Complement number to its positive & the result should be 0
     • Hex number system
       • Base 16
         • 0 to 9, then A to F
           • To convert from binary
             • Split the 8 bits into 2 nibbles
               • Work out the denary of each nibble. eg. 1010 = 10
                 • Convert the denary to hex
                   • 10 in hex = A
       • Used for IPv6 addresses
       • Used as easier for humans than dealing with large binary numbers
       • Used for colour codes

2. Networks

   • Toplogies
     • Means how a network is connected
     • Bus
       • Simplest & cheapest
       • Easy to add new devices
       • Gets data collisions which is a -ve
       • If one node fails, the whole network fails
       • 1 cable
       • East to set up and manage
     • Ring
       • 2 cables
       • Removes data collisions
       • Cheap
     • Star
       • Data goes through a switch (board)
       • If 1 device fails, the whole network doesn't go down
       • Needs specialist equipment & management
       • More expensive as needs more hardware & expertise to run it
     • Mesh
       • Internet is a mesh network
   • LAN
     • Local Area Network
       • On one site
   • WAN
     • Wide Area Network
     • Across a wide geographical area
     • Internet is a mesh network & a WAN
       • The Internet
         • Protocols - rules for sending & receiving data
           • Application Layer
             • Web
               • FTP
                 • File Transfer Protocol
                   • Uploading & downloading files
               • HTTP
                 • Hypertext Transfer Protocol
                   • Sending and receiving of web pages in HTML
                     • Hypertext Markup Language
                       • Defines how web pages will look
               • HTTPS
                 • Secure HTTP
                   • Data is encrypted before sending
                     • Data is secure as can't be decrypted if intercepted by hackers
             • Email
               • SMTP
                 • Simple Mail Transfer Protocol
                   • For sending emails only
               • POP
                 • Sending & receiving emails
                   • Emails are deleted from the server when read
                     • Only exist on the device that first accessed it
               • IMAP
                 • Internet Message Access Protocol
                   • Sending and receiving of emails
                     • Emails aren't deleted from the server
                       • Can be read again from anotjher device
           • Transport/Internet Layer
             • TCP
               • Transmission Control Protocol
                 • checks no data is missing from sent packets
                   • Uses checksums
             • IP
               • Internet Protocol
                 • Splits data into packets
                   • Addresses packets
                   • Header
                     • Sender & receiver address. Number of packets and packet number
                       • Like the envelope on a letter
                   • Body
                     • The message
                       • Like the contents of the letter
                   • Footer
                     • 'End of packet info
                       • Like the signature on a letter
               • IP addresses
                 • unique to each device on the internet
                 • IPv4
                   • 4 sets of decimal numbers
                 • IPv6
                   • 8 blocks of 16 bit hex numbers
           • Another Truck Is Late
           • Link Layer
             • Network layer
               • How data travels on the local network
                 • Ethernet protocol
                 • WiFi protocol
   • Client-Server
     • Client/Node
       • Any device on a network
     • Server
       • computer dedicated to 1 job. eg. media, printing, email
   • Peer-To-Peer
   • Hardware
     • Switch
       • Connect clients to a server without data going through all devices
     • Hub
       • Connects clients to a server but data goes through all other clients.
     • Router
       • Connects networks together
       • Routes data packets along a network
   • Network Security
     • Threats
       • Hacking
         • Unauthorised access to data
       • Viruses
         • Aim: to disrupt a network
       • Spyware
         • Keyloggers
           • Aim to steal passwords & other personal data
             • Unauthorized access to data
       • Social Engineering
         • Predicting how people will act
           • Phishing emails/texts
             • AIM: to capture personal data or to download a keylogger or virus on to a device
       • Ransomware
         • AIM: to get money
         • Encrypts data on a device & demands money to decrypt
     • Protection
       • Antivirus software
       • Anti spyware
       • Firewall
         • Hardware or software designed to prevent hackers
       • Education
         • No memory sticks
         • Do not download from unknown emails
       • Ethical hackers
         • Hack for good
       • Penetration Testers
         • Test networks for weaknesses
   • Transmission Media
     • Ethernet
       • Copper wire
     • Fibre Optics
       • Light along fine glass cables
         • Very fast
       • Most expensive
     • Wireless
       • no cables
         • cheaper
       • less reliable
       • 3G/4G/5G
       • WiFi
       • Bluetooth
     • Wired
   • Network Data Speed
     • bits per second bps
     • kilobits per second kbps
       • 1 kilobit = 1000 bpss
     • megabits per second mbps
       • 1 megabit = 1000 kbps
     • gigabits per second
       • 1 gigabit = 1000 mbps

3. Logic Gates

   • AND
   • OR
   • NOT
   • TRUE or FALSE
   • Truth tables

4. SOFTWARE

   • Operating system
     • Manages inputs/outputs
     • Manages files & folders
     • Manages application software
     • Runs the GUI
     • Manages scheduling
       • Use of the CPU by programs
     • Manages paging
       • Virtual memory
       • Switching between RAM & hard disc
   • Application software
     • eg. Word, Powerpoint, Graphics software
     • Tasks previously done on paper
   • Utility Software
     • Basic tools
       • eg. text editor, calculator, command prompt
     • File management
       • Back up
       • Defragmenter
       • Compression Tools
     • Security
       • Antivirus
       • Anti spyware
       • Firewall

5. Hardware

   • Von Neumann architecture
     • CPU
       • Fetch - Decode - Execute cycle
         • Fetch
           • Gets the instruction from a memory address
         • Decode
           • Analyses the instruction & sends signals
         • Execute
           • Instruction is carried out by CPU
       • ALU - arithmetic logic unit
         • calculations & logic operations
         • Accumulator - holds results of ALU operations
       • Registers
         • Memory locations
           • Accumulator
           • Program Counter
             • Holds address of next instruction
       • Control Unit
         • Controls & organises other parts of the CPU
       • Clock
         • synchronises the actions of other parts of the CPU
           • Speed measured in GHz
       • Buses
         • connections between devices in a computer
         • Bus width - sets how many binary numbers can be transmitted
           • 8-bit can send up to 256 values
           • More bits = faster data transmission
     • Memory
       • RAM
         • Volatile
         • Running programs. eg. the OS
       • ROM
         • Non volatile
         • Firmware/ BIOS
       • Cache
         • faster memory, accessed by CPU
     • Input/Output
       • Peripherals
         • Mouse, keyboard, printer, scanner etc.
   • Embedded systems
     • Single-purpose computer system
     • Usually part of a bigger system. eg. car, washing machine
     • Cheap, low power, simple
     • Often use sensors as input devices

6. Programming Languages

   • Low Level Language
     • Instruction set
       • list of commands the CPU can carry out
     • Machine code
       • the binary codes making up the instruction set
         • Instruction set
     • Assembly language
       • Written using mnemonics
   • Translators
     • Translate program code into machine code
       • Machine code
     • Assembler
       • Translates assembly language
         • Assembly language
   • High Level Languages
     • eg. Python, Java, C+
     • need translating into machine code to run
       • Compiler
         • Translates program all in one go
           • Saves as a .exe executable file
         • Code must be error-free to be compiled
       • Interpreter
         • Translates line by line as the program runs
         • Finds errors as program runs
         • eg. Python Shell

7. The Bigger Picture

   • Green issues
     • E-Waste
     • Energy use
     • Use of raw materials
     • Negatives
     • Positives
       • Sensors monitoring climate change
       • Early warning systems. eg. tsunamis
       • Tracking animals for conservation
   • Privacy
     • Data Protection
       • GDPR
         • Secure
         • Relevant
         • Accurate
         • Up to date
         • Specific use only
     • Surveillance
       • CCTV
       • Tracking services
   • Cyber Security
     • Computer Misuse Act
       • Against hacking
   • Digital Inclusion
     • Access to tech for all
       • Disability, rural areas, 'third world', age, income
     • Important for education, democracy, economy, not feeling isolated
   • Legal Issues
     • Copyright Law
       • Patents
       • Creative Commons Licensing
     • Piracy
     • Proprietary v open source software