slr4 - operating systems Flashcards
What is the purpose of the operating system
Create an interface for the user to interact with hardware
How do computers handle multitasking
Each program is given a small amount of time to execute an instruction before it switches to another program
What is the purpose of user management
Allows multiple users to log on to the same computer
The OS will save settings as well as controlling what files they can access
What is a WIMP interface
An interface that features windows, icons, menus and pointers
What is the role of a scheduler
Managing which process to execute next and how long it shoud execute for
What are the 5 scheduling algorithms
First Come First Served (FCFS)
Shortest Job First (SJF)
Shortest Remaining Time (SRT)
Multi-Level Feedback Queue (MLFQ)
Round Robin
Describe FCFS
Processes are executed in the order that they arrive in the queue
They are executed until they are completed
Describe SJF
Picks the process with the least time remaining and runs it until it is finished
Describe the round-robin scheduling algorithm
Each program is given the same amount of time to run before exiting the CPU
Describe the SRT scheduling algorithm
The program with the least amount of time is selected however it is pre-emptive so can suspend currently running programs if one with a shorter time becomes available
Describe process blocking
When a process requires certain conditions, it is put into a blocked state until the conditions are met
Describe MLFQ
When multiple queues are used for different cores
What are the 2 methods of dividing programs stored in RAM
Paging and segmentation
Describe Paging
Programs are split into pages of fixed sizes
Give a disadvantage of paging
It doesn’t account for how the program is split. this could mean that the program runs less efficiently
Describe segmentation
Programs are split into logical divisions
What is virtual memory
When the OS uses secondary storage to store programs instead of RAM
what is an interrupt
When another process signals to the processor that it wants attention
What is the ISR
The intercept service routine is a program with its own set of instructions that need to be fetched, decoded, and executed to carry out the interrupt
What does the contents of the program counter need to be changed to at the start of an interrupt
The address of the interrupts first instruction
What happens to the values stored in registers after an interrupt is received
The values are pushed into a stack
What happens to the stack after the interrupt is completed
The frame of the stack is “popped” off, meaning that all the original values are retrieved and loaded back into the necessary registers
Give some examples of high priority interrupts
PSU failure
Moving the pointer
Arithmetic overflow
What are the 5 types of operating system
Multitasking
Multi-user
Distributed
Embedded
Real-time
