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computing paper 2 - Coggle Diagram

- - - - inputs can either be on(1) or off(0)
    - - 2 inputs and 1 output
      - output is on(1), only is BOTH inputs are on(1)
      - symbol = A.B = C
      - truth table / AND gate
    - - if either input is on(1), the output is on(1)
      - 2 inputs and 1 output
      - symbol = A+B = C
      - truth table / OR gate
    - - 1 input and 1 output
      - outputs the opposite of the input
      - truth table / NOT gate
      - symbol = Ā
    - - multipul inputs and 1 output
      - if there is an ODD amount of on(1) inputs, the output is on(1)
      - symbol = A⊕ B = C
      - truth table / XOR gate
  - - - eg: CPU, motherboard, power supply
    - - eg: keyboards, speakers, printers
      - 3 catergories of external hardware
        
        input devices
        
        any piece of hardware that provides an input to the coputer
        
        eg:a mouse or keyboard which click/type
        
        output devices
        
        hardware that outputs a result from the computer
        
        eg: a printer which prints information
        
        storage device
        
        hardware that saves data for use at a later date
        
        eg: USB stick, CD
  - - - eg: word processors, spreadsheets, we browsers
    - - operating system
        
        communicates with the hardware and allows programs to run - user inteface, file and security management
        
        CPU management
        
        manages time allocated to each application on the CPU
        
        memory management
        
        manages memory allocated to program - also deals with virtual memory and swapping pages in and out of RAM
        
        peripheral management
        
        the OS has different device drivers which communiate with the hardware
        
        applications
        
        the OS allcates memory for an app, loads the application into RAM and begins executing the program
        
        security
        
        the OS is responsible for user management tasks (accounts, usernames and passwords)
      - utility software
        
        maintains the computer system - tend to run in the background or be used by applications in order to get tasks done (eg: anti-virus software)
        
        firewall
        
        a network seurity device that moniters and filters incoming and outgoing network traffic
        
        defragmentation
        
        the process of reorganising the data stored on the hard drive so that related pieces of data are put back together, all lined up
        
        system diagnosis
        
        a computer utility which is used to test a computer system for the purpose of identifying weak point
  - - - volatile memory - only stores information to run programs while the computer is on - requires electricity to store data usig transistors and capasitors
      - non volatile - can retain data even when computer is switched off (eg: ROM and secondary storage)
    - - can directly access any memory location in a random order
      - data from the secondary storage is COPIED onto the RAM for execution
      - data is constantly being read from and written onto the RAM
      - data is stored temporarily - volatile
    - - used to store BIOS information on computer
        
        loading the device drivers (checking hardware and peripherals)
        
        leads up to loading the default OS
      - the special program stored in ROM is called the bootstrap loader
      - read only cannot be edited
      - where data is stored permanantly - non volatile
    - - all basic information nedded to load progams and application
    - - part of seconday storage
      - extention to RAM
      - temporary / volatile
      - when there is no more room on the RAM the applications not being used are moved onto virtual memory until app is needed and is moved back onto RAM to be used
      - the process of moving the data of the application back and forth between RAM and virtual memory is called swapping or paging
  - - - capacity - how much disk space oe or more storage devices provide - how much data is can contain
      - speed / data rate - the speed at which data is transfered within the computer, measured in bytes per second
      - portability - the ability of software to be transferred from mone system to another / how easily is can be transported
      - cost - cost of purchasing or maintaining the device
      - reliability - how long a device will work without breaking down
      - durability - how robust / strong it is
    - - solid state drives (USB)
        
        use flash memory
        
        built from special types of transistors that do not lose their state when power is switched off
        
        control gate selectors - for rows / similar to sectors
        
        writing info - add electrons - lots of electrons = 0 - fewer electrons = 1 - 000 --> 111
        
        stored in stacks - 3D format
        
        memory cell - 1 charge trap flash - trap pushes out electrons
      - optical storage devices (CD,DVD,blu-ray)
        
        use a laser to scan the surface of a spinning disk made from metal and plastic
        
        the disk surface is divided into tracks, with each track containing many flat areas and hollows
        
        the flat areas are known as LANDS
        
        hollows are known as PITS
        
        when the laser shines on the disc durface, lands reflect the light back while pits scatter the laser beam
        
        a sensor looks for the reflected light this is then represented using a '1' (lands = '1') while when no light is detected it is represented as a '0' (pits = '0')
        
        different types of optical media
        
        ROM media - pre written data that cannot be overwritten (eg: music, films software and games)
        
        read media - blanc discs where optical device writes data onto them by shining a laser onto teh disc - burns pits to represent '0' - can only be written once but can be read many times
        
        read/write - similar to read media but can be rewritten more than once
        
        ADVANTAGES
        
        can transfer easily between computers
        
        relatively cheap for small amounts of data
        
        DISADVANTAGES
        
        can scratch easily - not durable
        
        not much storage compared to others
        
        limited writes to hard drives - not reiable
        
        reflective surface
        
        laser beam - smaller wave length = smaller diameter of pit - more info stored
        
        photo electric cell - captures light reflected by land which can be processed by computer
        
        lands and pits
      - magnetic storage devices (hard disk drives - HDDs)
        
        use magnetic fields to magnetise tiny individual sections of a metal spinning disk
        
        each tiny section represents 1 bit - a magnetised section represents '1' and a demagnetised section = '0'
        
        sections are so small that disks can contain terabytes of data
        
        when the disk is spinning a read/write head moves across its surface
        
        to write data
        
        the head magnatises or demagantises a section of the disk that is spinning under head
        
        to read data
        
        the head makes a note of whether the section is magnetised or not
        
        tracks / sectors of disc
        
        actuator arm - allows access to data
        
        head - magnetises secors of disc / reads info
        
        disc platter - stores all discs together
        
        ADVANTAGES
        
        cheaper than other types of secondary storage
        
        capacity - can store lots of data
        
        DISADVANTAGES
        
        reliability - contains moving parts so can get damaged easily
        
        speed - read/write of info is slow
        
        electromagnetic surge can corrupt/damage the data stored
  - - - emmbedded computer
        
        actuator output
        
        feedback
    - - sensorts - takes in input
      - analogue to digital converter (ADC) - converts input signal into digital data
      - actuators - mechanical device that carries out the processed info
    - - smaller - takes up less space
      - inside main system
      - easier to replace if broken
      - uses less power
      - no moving parts - more robust
      - cheaper to produce
      - efficient software
    - - if emebedded stystem breaks so does whole system
      - specialised skills needed to fix / make
  - - - considered the brain of the computer system - processed all data and instructions that make the system work
        
        main parts of CPU: ALU (Arithmetic and Logic Unit) / Control Unit (manages data) / the clock (number of instructtions the can be performed ) / buses (moves data around)
        
        ALU
        
        responsible for performing all calculations and logic expressions in the computer
        
        Control Unit
        
        overall control of CPU - main job is to execute program instructions - controls the flow of data in and out of the CPU
        
        clock
        
        determines when instructions are processed - ticks at a specific rate - each tick allows one instruction to be processed by CPU - Hz
        
        buses
        
        collection of wires through which data is transmitted from one component to another
      - input device
        
        CPU
        
        memory unit (RAM)
        
        output device
    - - fetch - the next instruction is fetched from RAM to CPU
        
        decode - instruction is decoded to work out what it means
        
        exectute - the instruction is executed
      - (1) program counter - increases by 1 each time
        
        (2) MAR - address that will be fetched is stored
        
        (3) main memory - holds data (RAM)
        
        (4) MDR - holds value of data
        
        (5) cache - copy of repeated data/instructions
        
        (6) control unit - decpodes instruction/data and decides what to do with it
        
        1 more item...
      - registers
        
        MAR - memory address register
        
        holds the address of the current instruction that is to be fetched from memory, or the address in memory to which data is to be transferred
        
        MDR - memory data register
        
        holds the contents found at the address held in the MAR, or data which is to be transferred to main memory
        
        CIR - current instruction register
        
        holds the instruction that is currently being decoded and executed
        
        ACC - accumulator
        
        holds the results of processing
        
        PC - program counter
        
        holds the memory address of the next instruction to be fetched from main memory
      - inproving performance of CPU
        
        clock - the faster it ticks the more instructions are executed per second
        
        by increasing clock speed it increases speed of CPU - however if clock ticks too fast (over ticking) it causes overheating of motherboard and computer crashes
        
        multi core CPU - internal compnents of CPU duplicated so 2 instructions can be executed every tick
        
        slight delay in buses so not exactly twice as fast but still faster
        
        cache - tmporarily stores data and instructions that CPU is likely to reuse
        
        means CPU does not need to go back through the whole cycle if the instruction is in the cache - speeds up performance
        
        L1 cache - very fast but cannot store that much data (8 - 64 kb) - this is because of size limitations and expensiveness
- - - - 1011(11) x 2 = 10110(22)
    - - -1 if the last digit is a 1
      - 10111(23) / 2 (-1)= 1011(11)
  - - - 7 bits - can store 128 characters
    - - 8 bits - 256 characters
    - - 24 bits - over 16 million characters
  - - - 1 bit = 2^1 = 2 colours
        
        2 bits = 2^2 = 4 colours
        
        3 bits = 2^3 = 8 colours
        
        16 bits = 2^16 = 65,536 colours
      - 2^number of bits/colour depth = number of colours
  - - - analogue wave --> measure height of sound wave at regular intervals (number of bits) --> this is then stored in a computer as binary code --> digital waves/data
  - - - lossy
        
        reduces size of file bupermanently deleating data - ;ower quality
        
        PRO
        
        very effective
        
        can make file as small as you want
        
        CON
        
        cannot be reversed
      - lossless
        
        uses an algorithm to represent repeated data to reduce file size
        
        PRO
        
        reversable
        
        CON
        
        not suitable for all files - needs to have a lot of repetition
        
        run length encoding (RLE)
        
        AAAAAHHH!!!!
        
        5A
        
        largest frequency
        
        3H
        
        4!
        
        ASCII = 7 bits
        
        original file size = 12 characters x 7 bits = 84 bits
        
        compressed file
        
        5 (largest frequency) = 101 (as a binary number) = 3 bits --> only 3 bits needed to represent frequency
        
        (3 bits (frequency) + 7 bits (ASCII)) x 3 characters = 30 bits
        
        saved file = 84 - 30 = 54 bits saved
        
        :blue_heart::blue_heart::blue_heart::blue_heart::<3::<3::green_heart::green_heart::green_heart::green_heart::<3::<3:
        
        4 blue
        
        largest frequency
        
        4 = 100 = 3 bits - number of bits needed to store frequency
        
        2 red
        
        4 green
        
        2 red
        
        colour depth = 3 colours = 11 (binary) = 2 bits
        
        compressed file = (3 frequency +2 colour depth) x 4 groups = 20 bits
        
        huffaman coding
        
        a type of lossless data compression - uses a lower number of bits to represent data that appears more often
        
        ABRACADABRA
        
        A: 5
        
        = 11
        
        B:2
        
        C D B R A
        
        1 1 2 2 5
        
        3 more items...
        
        R:2
        
        C: 1
        
        D: 1
        
        11 charcters x 7 bits (ASCII) = 77 bits - original file size
- - - - field = a column - must have a data type
        
        integer - whole number
        
        float/real/decimal - decimal number
        
        char - fixed length string up to 8,000 characters
        
        varchar - variable length string up to 8,000 charaters
        
        text - variable length string up to 2GB of data
      - record = a row
      - table
      - table name
      - field name
    - - stores a single table of data inside a single text file (usually CSV format)
      - each record appears as a separate line
      - each field is separated by a comma
      - issues with flat file databases
        
        we often have to repeat data in each record
        
        this leads to inconsistencies in data - harder to search/sort data
        
        also leads to redundant data (repeated data) - so database uses more memory/storage than it needs - longer to search
    - - has more than 1 table, each linked via relationships
        
        relationships = made by linking the primary key to foreign key - primary key in one table = the foreign key in the other table +another primary key in that table
      - often used to avoid data inconsistencies and redundancies
    - - one to many
      - one to one
      - many to many
  - - - BETWEEN - between an exclusive range
      - LIKE - search for a pattern/character or word