Systems software - paper 1 Flashcards
What is an operating system?
A collection of programs that work together to provide an interface between the user and computer
What functions do operating systems provide?
Memory management
Recourse management
File management
Interrupt management
What is paging?
When memory is split up into equal sized sections known as pages.
Individual or groups of pages can be swapped into main memory when needed
What is segmentation?
The splitting up of memory into logical sized divisions, segments that vary in size.
What is virtual memory?
When there is not enough space in the RAM part of the secondary storage is used to act as RAM. Sections of programs not currently in use are moved to secondary storage temporarily.
What is the issue of using virtual memory?
Disk thrashing- When pages are swapped too frequently between the hard disk and main memory. This causes the system to slow. Becomes worse as memory fills up
What is an interrupt and how are they ordered?
Interrupts are signals generated by the software or hardware to indicate that a process needs attention.
Stored in order of their priority
What is the interrupt service routine?
The processor checks the contents of the interrupt register at the end of each FDE cycle. If an interrupt is there that is a higher priority than the process being executed the contents of the CPU are moved to a stack. The processor then loads the appropriate interrupt service routine into RAM. A flag is set to signal the ISR has begun. Once finished the flag is rest and the interrupt queue is checked again and then the FDE cycle resumes.
What are the different scheduling algorithms?
Round robin
First come first served
Multilevel feedback queues
Shortest job first
Shortest time remaining
What are the features of a round robin system?
Each job is given a time slice which it is allowed to execute within. Once its time is up the next time slice is loaded up and so on.
What are the features of a first come first serve algorithm?
Jobs are processed in the order that they enter the queue- there is no priority.
