operating systems

operating systems

1. Desktop Devices: Windows, Mac OS, Linux, Unix. Portable Devices: Android, iOS/Apple OS ,Chrome OS

   • Machine code instructions are different for each piece of hardware Each PC has a different combination of CPU, hard disk, memory manager, graphics card etc. Writing software to talk directly to every different piece of hardware on every different configuration of PC would be almost impossible
     • If we programmed directly for the hardware, we would have to implement all of these things manually An operating system deals with all the things mentioned above, leaving the program to only focus on its own functionality
   • The OS manages many parts of the computer so that the applications don’t have to, including: CPU multi-tasking interrupts memory backing store peripherals Security interface

2. CPU

   • Modern processors can execute 4 billion instructions every second. This is more than memory and secondary storage can keep up with While a processor waits for other components to catch up, it is not doing anything An OS will make use of this dead time by allocating CPU time to different processes A process is a running application Each application can run as if it is the only program on the system, and the operating system can allocate processor time as necessary, allowing multitasking

3. Multi-tasking

   • Multi-tasking is where a processor appears to be doing two tasks simultaneously In reality the processor runs commands from each task separately, filling in the time when it is waiting for other components.
   • This is a complex task – simply alternating the instructions will result in memory being overwritten The OS has to keep the tasks separate and manage use of the accumulator and memory locations.

4. Graphical User Interface (GUI)

   • A GUI is used by most PC and phone operating systems. Graphical representations of the computer’s functions are shown to the user and controlled by touchscreen or a mouse and keyboard. Programs often run in windows and several can be shown at the same time.
     • Advantages of GUI
       • Easy to learn. Lots of information shown at once
     • Disadvantages of GUI
       • Uses a lot of system resources. Complexity means there is more to go wrong

5. Command Line Interface (CLI)

   • A CLI is a text-based interface. The user types commands, and the result is shown as text. Nearly every operating system provides a CLI. These are harder to use, but are very lightweight and robust – they use few system resources and are very unlikely to crash or break
     • Advantages of CLI
       • Few system resources required. Easy to automate (commands can be stored in file)
     • Disadvantages of CLI
       • Hard to learn. Difficult to compare outputs of different programs