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Computer science - Coggle Diagram

- - - - Manage the hard drive
      - Creates a user interface.
      - Manages the applications stored.
    - - A process is a program being processed by the processor.
      - A single process executes 1 by one after one process and it can be interrupted each at a time.
      - A multitasking OS only allows one process to be executed at a time , yet allows other programs to run by rapidly switching between processes.
    - - When you have a program , it needs to be directly loaded to the ram.
      - The operating system allocates and manages RAM space.
      - If there is not enough memory , the OS may create virtual memory.
      - The bootstrap of an operating system of often stored in ROM.
      - Data and instructions are kept separately within the memory.
    - - Peripheral programs are hardware that can interact with the operating system. The OS creates drivers , which are derivers , to convert between peripheral signals and OS signals.
  - - - Machine code is the least abstracted language ; consisting of 1 and 0 , it only has 2 values to represent the different voltage levels that a computer understands.
      - Everything on a computer must be translated to machine code.
      - Every machine code language is specific to a family of processor as each use different sets.
    - - Assembly code is least abstracted and is still low level.
      - Assembly buse pnemonics to rember an operation. There are differnet assembaly language for different processor.
      - They have a mostly 1 to 1 relationship with machine code.
      - They consist of an operator which tells the computer what operation should be carried out and an operand which addresses the specific register locations.
    - - High level languages are the most abstracted as they use variables and other constructs to represent what is actually going on.
      - High level languages are much more like standard English.
      - They are very portable and could work on different computers.
      - They leave more work to be done at runtime , so the translator has got more work to do ; therefore . it can be slower to execute.
      - They can be easier to optomise.
  - - - Assembler
        
        An assembler translates assembly code into the machine code equivalent. it produces an object code file.
        
        Used because you can program directly . this is important because it does not use that much size.
        
        Optimization can occur.
      - Compiler
        
        A compiler goes through the entire code and converts it into machine code.
        
        Error messages are only shown after the whole code has been executed.
        
        Does not require the source code to run.
      - Interpreter
        
        Works line by line and executes the code.
        
        Requires the source code to run.
        
        The program stop
        
        Slower than a compiler.
  - - - Main memory is any memory that is directly accessible by the CPU.
      - Types.
        
        Cache
        
        Cache stores frequently used data.
        
        Cache sits between the processor and the RAM and is checked in the fetch execute cycle..
        
        Cache is volatile.
        
        ROM
        
        ROM comes in the form of a chip on the motherboard and can only be read. The data can not be changed.
        
        Stores the BIOS and firmware.
        
        The data is voletile.
        
        RAM
        
        Ram comes in sticks and comes in the computer. It stands for random access memory.
        
        Ram is very quick and it stores a copy of frequently used instructions that are currently in use from secondary storage , so it can be accessed quickly.
    - - Memory can either be volatile or non volatile. Volatile means that means that the memory is lost when there is no power supply / ORA.
    - - Secondary storage is memory that has not got a direct connection to the CPU.
      - Secondary storage is used to store programs in the longer term. For this reason, it is non volatile.
      - Types
        
        Binary data is stored on the variations of the height on the disk. The disk then spins at a high frequency. A light is shone on it and depending on weather it is a pit or a land , the binary digits 1 and 0 are returned to a sensor which decodes and interprets the data.
        
        Regions of the plater are either magnetized by the read weather head when it magnetizes or demagnetizes seating regions. this represents the 2 binary digits.
- - - - PAN
        
        A pan is a personal area network. It is a short range network and only exists around an individual person.
      - WAN
        
        A WAN is a network that connects nodes past geographical boundaries ; the largest WAN is the internet.
        
        Some of the infilstructure is owned by an ISP.
      - LAN
        
        A network that connects devices close to each other , usually around homes or schools.
    - - Client server networks
        
        On this network , a lot of clients connect to a server. The clients then connect to the server over a network and the network backs up the data centrally.
      - Perr to peer
        
        No central server.
        
        Each server has equal responsibility.
    - - Latency
      - Bandwidth
      - Errors.
    - - Wired connections are generally faster than wireless.
      - Bandwidth can be shared amongst the wired connections so can become congested.
      - Wireless has a small range and can be can be interfered with.
      - Wireless devices can lead to data collisions.