The operating system has several roles:
- Manage memory
- Schedules Programs to run
- Mangaes interrupts
- Provides a interface between the user and the computer
There are two ways of managing memory
- Paging – Memory is divided into equal fixed physical sized units called pages. Pages can be moved from main memory to virtual memory
- Segmentation – Memory is divided logically. Modules are shared between Programs
What is virtual memory?
When memory is full, the operating system dedicates some area of the hard drive area to memory. This increases the capacity of memory however virtual memory is very slow to send data.
How are interrupts processed?
Interrupts take place because of:
- Power Failures
- Driver Failure
An interrupt is sent to the CPU. All contents in the registers are stored in the interrupt register. The interrupt service routine takes place. The contents are put back into the register
What is scheduling?
There are five methods of scheduling tasks
- Round Robin
- First come first served
- Shortest job first
- Shortest time first
- Multi-level queu
What is round robin?
Each task is processed for the same amount of time
What is First come first served?
The first task that comes is processed first
What is Shortest job first?
The task that is smallest in size will be processed first
What is the shortest time first?
The task that will take the shortest amount to complete is processed first
What is multi-level queue?
The operating system assigns priorities to different tasks the tasks that have a higher prority are processed first