Hardware

Hardware

1. Graphical user interface (GUI)

   • The OS on most computers and smartphones provides an environment with tiles, icons and/or menus. This type of interface is called the graphical user interface (GUI) because the user interacts with images through a mouse, keyboard or touchscreen.

2. Command line interface (CLI)

   • An OS also provides a method of interaction that is non-graphical, called the command line interface (CLI). This is a text-only service with feedback from the OS appearing in text. Using a CLI requires knowledge of the commands available on a particular machine.

3. Multitasking

   • The OS makes it possible to run several programs at once. Several programs can be stored in RAM at the same time, however only one program at a time is processed by the CPU. Programs can be in one of three states:
   • running, waiting, runnable. Only one process can be running at any one time. CPUs are extremely fast, so if a program is processed for even a short time it can do quite a lot. The OS decides the best way to swap between running, runnable and waiting processes. It controls which process is being executed by the CPU at any point in time, and shares access to the CPU between processes. The job of working out when to swap processes is known as scheduling.
   • Swapping happens so fast that it appears that all processes are running at the same time. When there are too many processes, or some of them are making the CPU work especially hard, it can look as though some or all of them have stopped

4. Managing memory

   • The OS manages how main memory is used. It decides: 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 one another. This means they have to use different parts of the computer’s memory.
   • The OS handles the transfer of data between processes. This is done by setting aside areas in memory where data values can be shared. The OS uses buffering to set aside memory for the temporary storage of data. A process may output data and leave it in the buffer. This means that processes can each get on with their jobs at their own rate. It is only when the buffer is full that processes will need to wait. Buffers are also used when you stream online content.

5. Peripheral devices

   • Each peripheral is programmed with its own machine code. Each has its own rules that dictate how it transmits data values between the computer and the device. These rules make up a protocol for controlling and communicating with the device.
   • The protocol dictates the structure, speed and timing of the messages that are sent and received.
   • Drivers
     • The OS uses programs called device drivers to manage connections with peripherals.
     • A device driver: 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 received wakes up the device when it is needed and put it back to sleep when it is not
     • An OS will have generic device drivers to enable it to connect to most common peripherals. Some peripherals, however, will have their own drivers that need to be installed before use. 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 so they do not interfere with each other.