systems software Flashcards
what is an operating system
collection of programs that provide an interface between the user and computer
operating system functions
user interface
security
utility software
paging
memory is split into equal sized sections called pages that ca be swapped between main memory and hard disk
segmentation
splitting up memory into logical sizzed division which cqn vqry
virtual memory
uses section of hard drive to act as ram when there isnt enough space to store programs being used
when not being used they are moved to virtual memory using paging to free up space in ram
disadvantages of virtual memory
disk thrashing - computer feezes because of pages being swapped too often between hard disk and memory
so more time gets spent transferring these pages
what is an interrupt
signals generated by soft or hardware to indicate to processor that a process needs attention
interrupt service routine stages
ir checked at end of each fde cycle
if interrupt exits with higher priority to current process, the registers contents are transferred to a stack
isr is loaded into ram
flag signals isr has begun
flag is reset when isr finishes
ir checked again if no interrupts with a higher priority, stack contents are placed back into registers
fde cycle continues
what is scheduling
function of the operating system to ensure all sections being run recieve a faie amount of processing time
pre emptive meaning
jobs are made to start and stop by operating system
non pre emptive meaning
once job is started, left alone till completed
5 different scheduling algorithms
round robin
first come first served
shortest job first
shortest remaining time
multilevel feedback queues
round robin
each job is assigned a time slice to execute. after using its time slice job moves to back of queue and process is repeated till job is completed.
advantages and disadvantages of round robin
advantages
ensures fairness
disadvantages
longer jobs take more time to finish
doesnt consider job priority which can lead to inefficiency
first come first served
jobs are processed by which they entered the queue
