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
multilevel feedback queues
makes use of multiple queses, orded based on different priority
difficult to implement based on combination of priorities
shortest job first
jobs processed based on time required to complete.
most suited for batch systems
processor has to calculate how long each job takes and isnt always possible
shortest remaining time
jobs processed based on how much time is left for completion with jobs taking least amount of time first.
types of operating system
distributed
embedded
multi tasking
multi user
real time
distributed
run across multiple devices, load is spread across multiple processors
multi tasking
user can carry out tasks simultaneously
done by time slicing to switch between programs and applications in memory
multi user
multiple users make use of one computer
scheduling algorithm must be used to ensure processor time is shared fairly between jobs
real time
performs task within guaranteed time frame
time critical computer systems
bios
basic input output sstem
first program run when computers switched on
carries out three tests
3 tests of bios
post - power on sef test checking all hardware are connected and functional
checks spu, clock, memory and processor is operational
tests for external memory deviced connected to compute
device drivers
computer programs provided by os and allow os to interact with hardware
what does device driver do
communicates hardwares request to os which produces output
specific to computers architecture
virtual machine
theoretical computer that is a software implementation of a compuer system
intermediate code
halfway between machine and object code
can be used across different machines and os
uses of virtual machines
development enviroment for programmers
protection from malware
running incompatible software
uses of virtual machines
development enviroment for programmers
protection from malware
running incompatible software
