1.2.1 Systems software - Gurjot Flashcards
what is an operating system
a collection of programs that work together in order to provide an interface between the user and the computer
state some features that an operating system provides
- memory management
- file management
- utility software
- user interface
what is paging
when memory is split up into equal sized sections (called pages). these can be swapped between main memory and hard disk as needed.
what is segmentation
splitting up memory into logical sized divisions (called segment).
what is virtual memory
using a section of hard drive to act as RAM when the space in the main memory in insufficient. sections currently not in use are moved into virtual memory through paging
what are the issues with the 3 ways of memory management
it causes disk thrashing (when the computer freezes as pages are being swapped too frequently between hard disk and main memory.)
what are interrupts
signals generated by software or hardware to indicate to the processor that a process needs attention
describe the steps of the interrupt service routine
- processor checks interrupt register after every FDE cycle
- if an interrupt exists of higher priority than the current process being executed, current content in the registers are transferred into a stack
- the processor loads the appropriate ISR into RAM
- flag is set to signal ISR has begun
- once completed, flag is reset, interrupt register is checked again, if there is something of higher priority, the cycle begins again
- else the content of the stack are transferred back into registers in memory and FDE cycle resumes
what is pre-emptive scheduling
jobs are actively made to start and stop by the operating system
give examples of pre-emptive scheduling
- multi level feedback queues
- shortest time remaining
- round robin
