Operating Systems

Operating Systems

1. User Interface

   • UI
     • The UI allows the user to interact with the machine
     • Graphical or text based
   • GUI (Graphical User Interface)
     • Tiles, icons and/or menus
     • Allows the user to interact with images
       • Keyboard
       • Mouse
       • Touchscreen
   • CLI (Command Line Interface)
     • Text only
       • Feedback from machine is text
       • Input is text
     • Advantages:
       • Faster way to get tasks done
       • More flexible then GUI
       • Uses less memory
     • E.G. Minecraft Commands

2. Managing the CPU

   • Processes:
     • 1. Program is found on the storage
     • 2. a section of RAM is reserved + space is allocated for the program's data
     • 3. The program code is copied from storage into reserved memory
     • 4. The CPU program counter is set to the memory location of the first instruction in the program, and execution begins
   • Multitasking
     • OS makes is possible to run multiple programs at once
       • States:
         • Running
         • Waiting
         • Runnable
         • Only one process can be running at any one time
         • The OS decides the best way to swap between states
           • Swapping happens so fast that it appears as if all processes are running at the same time
           • When the CPU is overloaded it appears as if some or all processes have stopped
       • OS controls which processes are being executed by the CPU at any one time
     • Scheduling: Working out when to swap processes

3. File systems

   • The OS organises files on the storage drive
   • In order to retrieve data from a file, the computer needs to know:
     • Which storage device it is held on
     • Where it is stored on the device
     • How files are organised on the device
     • How much data is on it
     • The protocol needed to communicate with it
     • The OS maintains this information for other programs by providing a file system
       • Provides a uniform way of storing and retrieving data
   • File management
     • OS manages how data is organised into files
       • Makes it easier for the user to see files
       • Organises where and how files are stored, deleted, read, found and repaired
       • Also detects errors such as missing disks or incorrect file names, and informs the user that errors have occured
     • Windows File Explorer
     • Mac OS X Finder
     • Each file has a unique name and the OS maintains a set of look-up tables that relate to file names to locations on storage drives
   • Hierarchies
     • Inside each folder can be sub-folders and files. If you need to access a specific file, you just need to know how to look for it
     • Most files systems are hierarchical and contain directories that contain lists of other files
     • Similar to a tree: the branch point are the directories that lead to other files. Data files are at the ends of the branches and these is include files containing program code
     • File systems can become corrupt if a computer is turned off before a program is copied to a new location

4. Peripheral devices

   • Peripherals are programmed with their own machine codes
     • Machine codes dictate how the peripheral transmits data between the computer and the device
       • This makes up a protocol for controlling and communicating with the device
   • Drivers
     • The OS uses programs called device drivers to manage peripherals
     • - Handles the translation of requests between a device and the computer
     • - Defines where a process must put outgoing data before it can be sent, and where incoming messages will be stored when they are recieved
     • - Wakes up the device when it is needed and put it back to sleep when it is not
     • OS provides basic device drivers to enable it to connect with common peripherals. Some peripherals require their own drivers to be installed
     • Peripherals that use the same protocol may be controlled by the same driver. If a number of identical game controllers are plugged in, each device will store its data in a different place to avoid interfering

5. Managing Memory

   • OS manages main memory
     • How memory is shared between processes
     • What happens when there is not enough main memory to get the job done
   • Different processes running at the same time must not interfere with each other
     • Processes must use different parts of the memory
       • OS handles data transfer between processes
       • Areas in the memory are set aside
   • Buffering
     • Setting aside memory for the temporary storage of data
     • Processes can output data and leave it in the buffer
       • Allows processes to get on with their job at their own rate
       • When the buffer is full, processes have to wait
     • Also used to stream online content

6. Windows

7. Linux

8. Mac OS

9. Android

10. iOS

11. An Operating system is software that manages computer hardware and software. It supplies an interface for the user and important utilities for managing the computer