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Computer science, 1.5 systems software, addressing - Coggle Diagram

- - - - common CPU components and their functions
        
        ALU (Arithmetic Logic Unit)
        
        CU (Control Unit)
        
        cache
        
        registers
        
        The fastest component in the CPU
        
        hold specific data for the fetch-decode-execute cycle
        
        PC (Program counter)
      - the purpose of the CPU
        
        the fetch decode execute cycle
        
        fetch
        
        the next instruction is fetched from the RAM
        
        decode
        
        the instruction is decoded so that it can be performed
        
        execute
        
        any processing is done by the ALU
      - Von Neumann architecture
        
        MAR (Memory Address Register)
        
        stores the address of data which is either being sent to or being fetched from RAM
        
        MDR (Memory Data Register)
        
        Program counter
        
        accumulator
        
        Here results from the ALU are stored
    - - common characteristics of CPUs which can affect the performance
        
        clock speed
        
        The number cycles the CPU can execute per second
        
        clock speed is generally faster in newer devices
        
        cache size
        
        cache is a small amount of high speed RAM built directly within the processor
        
        the bigger the cache, the less time the computer has to wait for its instructions to be fetched
        
        number of cores
        
        the more cores a computer has, the more instructions it can process in a given space of time
        
        most modern computers are dual or quad core processors
    - - purpose
      - examples
  - - - the need for primary memory
        
        so that data can be written to and read from a location extremely quickly
      - virtual memory
        
        located in the hard drive
      - differences between RAM and ROM
        
        RAM - volatile
        
        ROM - non volatile
      - the purpose of RAM
        
        a platform that can be constant written to and read from
      - purpose of ROM
        
        to store data that is not lost when the electricity is turned off
    - - the need for secondary storage
        
        required to keep programs and data indefinitely
      - common types of storage
        
        optical
        
        examples - Blu ray DVDs
        
        uses lasers
        
        is damaged easily
        
        magnetic
        
        example - Hard Disk Drive (HDD)
        
        least expensive
        
        has moving parts
        
        solid state
        
        currently the most expensive
        
        really fast
        
        example - memory stick
      - advantages and disadvantages of different storage devices
        
        capacity
        
        speed
        
        highest to lowest - Solid state, magnetic, optical
        
        portability
        
        durability
        
        highest to lowest : solid state, magnetic, optical
        
        reliability
        
        most to least - solid state, magnetic, optical
        
        cost
    - - bit - 1
      - nibble - 4 bits
      - byte - 8 bits
      - kilo byte - 1024 bytes
        
        1 * 10 ^3
      - megabyte - 1024 kilobytes
        
        1 * 10^6
      - gigabyte - 1024 megabytes
        
        1 * 10^9
      - terabyte - 1024 gigabytes
        
        1 * 10^12
      - petabyte - 1024 terabytes
        
        1 * 10^15
      - converting denary to binary
        
        denary is base 10, which requires conversion into binary, which is base 2. starting at 1, ones are written underneath numbers which sum to the denary number being converted. see below for a diagram
        
        link to www.google.com
      - data capacity - practice data capacity calculations
    - - numbers
        
        converting positive denary numbers to binary
        
        see explanation in 1.2.3 'units'
        
        adding two binary integers together
        
        1 + 1 = 0 (and 1 carried over to the next column)
        
        1 + 0 = 1
        
        1 + 1 (+ a carried one from the previous column) = 1 (and 1 carried over to the next column)
        
        converting positive denary numbers to 2 digit hexadecimal numbers and vice versa
        
        first you must convert the denary number to its binary equivalent
        
        then split the eight bit binary number into two, with four bits each. if the first, or second, or both parts are above 9, letters are used:
        
        hexadecimal binary values for letters
        
        A - 1010
        
        B - 1011
        
        C - 1100
        
        D - 1101
        
        E - 1110
        
        F - 1111
        
        converting binary whole numbers to hexadecimal and vice versa
        
        if there is a number less than or equal to 9, treat it as a denary number and find its binary equivalent
        
        if there is a letter, calculate its denary number, with A being 10, and convert that to binary
        
        binary shifts
        
        division (right shift)
        
        by 2 (one shift)
        
        by 4 (two shifts)
        
        by 8 (three shifts)
        
        all binary digits are shifted one, two or three places to the right, with the empty spaces filled in with 0s
        
        multiplication (left shift)
        
        by 2 (one shift)
        
        by 4 (two shifts)
        
        by 8 (three shifts)
        
        all binary digits are shifted one, two or three places to the left. the empty spaces left are filled with 0s
        
        overflow errors
        
        when a calculation is performed, but the computer cannot hold that amount of information correctly, as a result of it being outside of their predefined value range
      - characters
        
        as computers work in binary, all characters are represented as binary codes
        
        character set
        
        all the characters a computer can use
        
        e.g American Standard Code for Information Interchange (ASCII)
        
        uses 7 bits of binary, providing 128 different characters
        
        e.g Unicode
        
        uses 16 bits, providing over 65,000 different characters
        
        is used to store characters from every language, for example in Chinese or Arabic
        
        Extended ASCII
        
        uses 8 bits, which provides 256 different characters
        
        allows for special characters, such as accented letters in French or Spanish
      - images
        
        represented as a series of pixels, each with a separate binar code
        
        metadata
        
        means 'the data about data'
        
        can be things such as:
        
        the type of file:
        
        JPEG
        
        or GIF
        
        the resolution
        
        colour depth
        
        the effect of colour depth and resolution on
        
        quality
        
        the higher the resolution and colour depth, the better the quality of the image
        
        size
        
        the higher the resolution and colour depth, the larger the total size of the image
        
        resolution
        
        the level of detail the image contains, as a result of the small or large number of bits stored in each pixel
        
        colour depth
        
        the number of bits available for colours in an image
        
        are either
        
        bitmap
        
        vector
      - sound
        
        how sound is sampled and stored digitally
        
        sound recorded on a computer exists as digital info encrypted into an audio file
        
        how
        
        microphone measures change in air pressure
        
        microphone translates air pressure into electrical voltage
        
        the Analogue to Digital Converter (ADC) digitises the electrical voltage to bytes of data
        
        computer displays the digitised sound for manipulation
        
        effect of sample rate, duration, bit rate and depth on
        
        playback quality
        
        size of sound file
        
        duration
        
        for how long the file runs
        
        sample rate
        
        the number of audio samples taken per second
        
        bit depth
        
        the number of bits available for each clip
        
        bit rate
        
        the number of bits used per second of the audio
    - - types of compression
        
        lossy
        
        removes some of the file's original data to reduce size of file
        
        can result in small loss of quality of image or sound file
        
        lossy compression may reduce the number of colours in an image, for example
        
        lossless
        
        does not reduce quality of file at all
        
        no data is lost, and the file is recreated exactly as it when when originally formed
  - - - types of networks
        
        WAN (Wide Area Network)
        
        typically arranged over a large geographical area, such as a country
        
        LAN (Local Area Network)
        
        typically arranged over a small geographical area, such as an office block
        
        factors which affect the performance of networks
        
        Number of users
        
        Error rate
        
        Transmission media
        
        Bandwidth
        
        Latency
        
        Modes of connecting computers over a network
        
        Client-server
        
        Separates computers into clients and peers
        
        Roles of computers are acting both as servers and clients
        
        Client - a computer that relies on the servers to provide and manage data
        
        Server - a computer which manages and stores files
        
        Peer-to-peer
        
        Roles of the computer
        
        Store their own files , which can be accessed by other peers on the network. Computers act as both peers and clients
      - hardware needed to connect stand alone computers into a LAN
        
        Wireless Access Points (WAPs)
        
        connects computers to a network using Wi-Fi
        
        routers
        
        one of the most commonly used connection devices
        
        used to send data signals across the internet
        
        allow LANs to be connected to the Internet (a big WAN)
        
        switches
        
        allows packets of data to be transmitted to computers
        
        remembers which computers are connected to which ports (smarter than a hub)
        
        Network Interface Card (NIC)
        
        provides an interface port for wired connections
        
        often found built into the motherboard
        
        transmission media
        
        copper
        
        fibre optic
        
        carry data signals from one node to another
        
        are either wired or wireless
      - the internet as a wide collection of networks (WAN)
        
        Domain Name Server (DNS)
        
        Domain name servers receive domain name requests from the users, such as ‘bbc.co.uk’ and emit the network address, which consists of 4 sets of three digits and is difficult for the user to remember.
        
        hosting
        
        The storing of files and data on a web server
        
        The host is included on the URL of a website
        
        the cloud
        
        Servers can be used to store data and programs which are available to access over the internet
        
        The location in which these accessible programs are stored is called ‘the cloud’
        
        web servers and clients
        
        The internet largely works on the client-server model
        
        Web servers store and maintain web content, which is downloaded upon request by clients
        
        Star and partial mesh topologies
    - - modes of connection
        
        wired
        
        wireless
        
        encrption
        
        IP and MAC addressing
        
        standards
      - common protocols
        
        POP
        
        Post Office Protocl
        
        TCIP/IP
        
        Transmission Control Protocol
        
        Internet protocol
        
        Must follow the rules of:
        numbering the packets
        Doing an error check
        
        Enables communication over the internet
        
        SMTP
        
        Simple Mail Transfer Protocol
        
        Sends emails between mail servers
        
        HTTP
        
        Hyper Text Transfer Protocol
        
        Used to load pages of a website
        
        Governs communication between the web server and a client
        
        HTTPS
        
        Hyper Text Transfer Protocol Secure
        
        Includes secure encryption to allow transactions to be made over the internet
        
        FTP
        
        File Transfer Protocol
        
        Used to transfer files from a computer to a website
        
        IMAP
        
        Internet Message Access Protocol
        
        Governs retrieving emails from email servers
      - the concept of layers
  - - - Forms of attack
        
        Denial of service attacks
        
        When a hacker attempts to prevent a user form using a network by flooding it with useless data traffic to slow down network or make it completely inaccessible
        
        Passive attack
        
        When a criminal monitors and intercepts data travelling between networks. This is hard to detect as the attack it isn’t very obvious
        
        the best defence against this is encryption
        
        active attack
        
        When someone attacks a network with malware, which is easily detected
        
        Forms of malware access
        
        Virus
        
        Attach to files by copying themselves. Users spread viruses by opening and copying them
        
        worms
        
        Similar to viruses, by can self replicate without user help of data platforms, such as files. They spread at an extreme rate and exploit weaknesses in a network’s security.
        
        trojans
        
        Malware disguised as legitimate software, to trick receivers into opening infected files and installing viruses onto their device
        
        the best defence against active attacks are firewalls
        
        Insider attack
        
        When someone from inside an organisation exploits their position and steals information from the network.
        
        to defend your network against this type of attack, user access levels can be used
        
        brute force attack
        
        A type of active attack, using trial and error to attempt to crack passwords in order to gain information
        
        use automated software, which produces hundreds of likely passwords, for example, commonly used combinations of numbers
        
        if accounts are locked after a certain amount of attempts at the password, brute force attacks can be prevented. Strong passwords are also extremely helpful in prevention.
      - Actions of malware
        
        Scareware
        
        Telling the user that their computer is infected with viruses to scare them into paying for problems to be fixed or to follow dangerous links.
        
        spyware
        
        Secretly monitors the user’s actions to gain personal info, for example tracking keyboard inputs for passwords
        
        Rootkits
        
        Software which alters access permissions in order to gain administrator level on devices
        
        Ransomware
        
        Encrypts files on a computer, in order to charge the user for the decryption key to unlock all of their files now in cipher text
        
        Deleting or modifying files
    - - Common preventative methods
        
        Anti-malware software
        
        Designed to find and stop malware from destroying a device or network. An example is a firewall, which examines all data that enters and leaves the network.
        
        There is a wide variety of anti malware software, including anti virus programs which can isolate and eliminate viruses inside networks or computers
        
        User access levels
        
        Control which parts of the network different users can access.
        
        this prevents insider attacks, as those of lower authority don’t have access to sensitive data.
        
        Passwords
        
        Help prevent unauthorised users gaining access to the network and stealing sensitive information
        
        a strong password will have a large number of characters, and should consist of a random combination of letters, numbers and symbols
        
        Encryption
        
        When data is translated into cipher text to which only the user with the key can decipher, meaning that unauthorised users can’t read it
        
        Physical security
        
        Protects the physical hardware of the network, with components such as security cameras and padlocks
        
        Penetration testing
        
        When employees from outside an organisation check the security of a network by stimulating false attacks
  - - - user interface
        
        operating system provides a user interface which allows the user to interact with the machine. There are four different types.
        
        Graphical User Interface (GUI)
        
        very interactive based, has Windows, Images, Menu and Pointers (WIMP)
        
        most commonly used and is user friendly
        
        interactive and intuitive
        
        Natural Language (NL)
        
        lacks reliability
        
        responds to spoken commands
        
        Command Line (CL)
        
        only has the option for the user to enter specific commands for whatever action they desire the computer to perform
        
        for more advanced users, and those who have a limited amount of memory on their device
        
        only uses text
        
        Menu
        
        displays single choices for the user to manually enter in
        
        an example is a card machine
      - user management
      - peripheral management and device drivers
      - memory management and multitasking
        
        when the RAM runs out of space to store programs which are running, the operating system activates virtual memory to store background programs
      - purpose
        
        manage the hardware and software resources
- - - - Principles
        
        Abstraction
        
        Picking out the important parts of the problem and ignoring the insignificant details
        
        Decomposition
        
        Breaking the bigger problem into lots of smaller problems so that they are easier to solve individually
        
        algorithmic thinking
        
        A logical way of getting from the problem to the solution in a series of steps
    - - identify:
        
        inputs
        
        outputs
        
        processes
        
        common errors
      - structure diagrams
      - create, interpret, correct complete and refine algorithms using
        
        flowcharts
        
        Diamonds - decisions
        
        Rectangles with rounded edges - start/end (terminals)
        
        rectangles with pointed edges - processes
        
        Trapeziums - inputs/outputs
        
        Can be shown as:
        
        Sequences
        
        selections
        
        Iterations
        
        Pseudocode
        
        The simplest programming language used for writing programs simply when designing
        
        high level programming language (python)
      - trace tables
    - - standard search algorithms
        
        binary search
        
        Searches in an ordered list
        
        finds the middle item, compares it to the desired value and splits accordingly
        
        linear search
        
        Used on an un ordered list
        
        checks each item at a time
        
        better for shorter lists
      - standard sorting algorithms
        
        insertion
        
        Sorts the values as it goes, comparing each item to those behind it.
        
        merge
        
        Splits the list into pairs, then merges it back together, creating slightly bigger sun lists each time
        
        smaller lists are easier to sort than larger lists in this way
        
        it’s easier to merge two order lists than two unordered lists
        
        bubble
        
        Compares pairs of items
        
        are swapped if they’re in the wrong order.
        
        when following this process, the largest number ‘bubbles’ up to the top
        
        Easy to program
        
        not very efficient in large lists
  - - - Operators
        
        Assignment
        
        Used to assign values to constants or variables
        
        =
        
        comparison
        
        Greater than - >
        
        less than - <
        
        Basic arithmetic
        
        Addition - +
        
        subtraction - -
        
        multiplication - *
        
        division - /
      - Casting
        
        The action of converting a data type from one to another while the prgram is running
      - Data values
        
        Constants
        
        Variables which can not change whIle the program is running
        
        Variable
        
        Values which can be changed while the program is running
    - - Integer
        
        Whole numbers only
      - Boolean
        
        Can only take one of two values, generally true or false
      - floats
        
        Numbers which have a decimal part
      - characters
        
        Single letters numbers or symbols
      - strings
        
        Used to represent text as a collection of characters
    - - Boolean logic
        
        AND
        
        Both values have to be true to output true
        
        NOT
        
        Switches the output from its logical value
        
        e.g NOT(3=3) would be False
        
        OR
        
        If either values are true, the output Is true
- - - - rename
      - delete
      - copy
      - and move files
- - - - intuitive
      - resource heavy
      - easy to use - visual
      - has WIMP - Windows, Icons, Menus and Pointers
  - - - text-based
      - for advanced users
      - more efficient
- - - - defines how emails can be sent from a mail server to devices and other servers
      - stands for Simple Mail Transfer Protocol
      - used to send emails
    - - also used to retrieve emails from a server
      - server does not keep the original or a copy of the email - the email is deleted from the server after it has been downloaded
      - stands for Post Office Protocol
    - - keeps the original email on the server - therefore more preferable, as users can sync devices and use email on more than one node
      - stands for Internet Message Access Protocol
      - used to retrieve copies of emails from the server
  - - - sets rules for how device connects
      - splits data into packets
      - reassembles data once it reaches destination
      - checks data is correct
      - is the data's mother - manages it
    - - directs packets across the network
      - is the sat nav
  - - - used by web browsers to access websites and communicate with web servers
      - stands for Hyper Text Transfer Protocol
    - - stands for Hyper Text Transfer Protocol Secure
      - also used by web browsers, but encrypts the data to make it more secure
    - - used to access, edit and move files between a device and a network
      - most commonly used for the downloading of files from the server
- - - - split in 16 bit chunks
      - each chunk given a hex value
      - has 2^128 possibilities
      - chunks separated by colons
    - - split into 8 bit chunks
      - each chunk given by a denary num
      - has 2^32 possibilities
      - chunks separated by periods (.)