Operating systems Flashcards
what is the list of things the operating system povides
manages peripherals
provides security
controls access
provides a platfrom to run software
utilities for system management
allows multi-tasking
what are the types of UI
CLI
GUI
how to does a GUI provide a user interface
windows
icons/images
menus
pointers
How does a CLI provide a user interface
command lines in termals and etc
how does an OS provide security
usernames and passwords
priviledge policys i.e student can only view their files but teacher can view their students files.
What is the kernal
the centre of the operating system directly interacts with the hardware
what are the 5 types of operating system
distributed
multi-user
multi-tasking
embedded
real time
what is a distrubuted system
a distributed system uses multiple processors physicallly seperated to split tasks among them more powerful tasks completed quicker
what is a multi-user system when is it used
allows multiple users to be on he server at once without security issues
used when resources need to be accessed simulatneously
what is a multi-task system
allows multiple programs to run at once
never actually at once but appears like it
what is paging in memory management
pages are all fixed sizes
physical divisions
i.e splits memory into 4Kbs and splits the program in the same intervals
what is segmenting in memory management
segments are sections of the program
logical divisions
in order to fit free spaces
what is scheduling
scheduling controls how the processor time is allocated which allows for multi-tasking
what are the types of scheduling needed to know
round robin
first come first server
shortest job first
shortest time remaining job
shortest time remaining
multi-level feeback queue
How does round robin work
processor time divided equally among jobs
given time slices
pros and cons of round robin
low wait time
doesnt scale well more taskes smaller time slices less efficient
how does first come first serve scheduling work
first job in is processed then move ot the next
cons of first come first seve
processes may have to wait a long time
what is shortest job first
the job that requires the shortest processor time is completed first
what is shortest job remaining first
the job which requires the shortest processor time left is completed first
pros and cons to shortest job first
reduces wait time (the long jobs are done last)
can cause starvation
pros and cons to shortest time remaining
more efficient than shortest job first
can still lead to starvation
what is multi-level feedback queue
uses queues where each task has a priority
if a process uses to much processor time given low priority
if sat idel for too long priority is moved up
what is an interrupt used for
an interrupt is a way to signal to the CPU that a task needs the CPUs processor time
what is the interrupt service routine
complete the FDE cycle
check priority of the interrupt is higher than the priority of the current application
if yes contents fo the registers stored as a stack
the address of the interrupt is coppied into the registers
when the ISR is complete the previous stack is popped back into the registers
explain interrupt service routine [6]
completes current FDE cycle
interrupt register is checked
priority is checked
if higher
contents of registers are stored on the stack
Program counter is set to the address of the first interrupt instruction
when finished previous register stores are restored
FDE cycle resumes
two people need to access the same device explain how operating sytems can allow that
[6]
multi user operating system
different username and passwords for each of them to log in
different settings
personalise their experience
access control rights can be allocated to each user
only access their own files
improve security
state two sources of interrupts and why these sources have different priorities [4]
peripheral needs attention (i.e key board press)
power button / shutdown has been pressed
the shutdown must be handled immediately
it is important to provide a reponsive user experience
some interrupts are more important than other interrupts
state two similarities between paging and segmentation
both a form of dividing up a program in order to be stored in Main memory
both allow more data to be stored when there is an insufficient amount of free RAM i.e by splitting up or using VM
why is scheduling necarssary
in order to process as many jobs as possible
in as little time as possible
emsures all jobs are processed
efficient use of resources
why is Memory managing necarssary
organise main memory
by changing logical addresses into physical addresses
allowing the computer to run when RAM is full
protect programs from each other
split up Tasks
allocates memory to tasks
describe an embedded operating system [3]
any three from
Low level operating system
Stored in ROM
Designed to do a certain function
A system embedded into another device
describe the term utility software
Specialist system software
Often with the OS
designed to help maintain the program
What is the purpose of Anti-virus software [2]
prevents harmful program being ran or installed
if a virus is installed can be detected and removes it safely
