Functions Of An Operating System Flashcards
What is an operating system?
A program or set of programs that manages that manages the operations of the computer to the user
Where is the operating system stored?
Permanent storage
What is the part of the operating system that is responsible for loading programs and libraries?
Loader
Where is the loader held?
ROM
What dies the operating system do when the computer is turned on?
The loader in the ROM sends the instruction to load the operating system by copying it from storage to RAM
What are the functions of the operating system?
User interface, memory management, interrupt service routines, processor scheduling, backing store management, input and output management
What will memory management do if the user wishes to switch from one application to another in a separate window?
Each application must be stored in memory simultaneously
What does paging and segmentation do?
Making the optimum use of memory by splitting it into small section
What does a paging system do?
Divides memory into fixed size pages of 4Kb each and a process currently in memory may be held in several non-contiguous pages
What is segmentation?
The logical division of address space into varying length segments which depend on the program structure
What is virtual memory?
Using secondary storage as an extension of memory to make room for the next job which has a share of the processor time
If more virtual memory is used what happens to performance?
Performance deaerates
What is an interrupt?
A signal from a software program, hardware device or internal clock to the CPU
When does a software interrupt occur?
When an application program terminates or request certain services for the operating system
When does a hardware interrupt occur?
When an I/O operation occurs or an error like ‘the printer is out of paper’ occurs
Why are interrupts also triggered by a timer?
To indicate that it is the turn of the next process to have processor time
How is multi-tasking possible?
Because a processor can be interrupted
When is an interrupt service routine used?
When the CPU receives an interrupt signal, suspending execution of the running program or process and disables all interrupts of a lower priority
What is meant by processor scheduling?
The role the operating system plays by allocating processor time to each one as they compete for the CPU
What is meant by multi-tasking?
Carrying out smaller parts of multiple larger tasks in turn, the processor can give the appearance of carrying out several tasks simultaneously
What is the scheduler?
The operating system module responsible for making sure that processor time is used as efficiently as possible
What are the objectives of the scheduler?
Maximise throughput, be fair to all users on a multi-user system, provide acceptable response time to all users and ensure hardware resources are kept as busy as possible
What are the different scheduling algorithms?
Round robin, first come first served, shortest remaining time, shortest job first, multi-level feedback queue
How does round robin scheduling work?
Processes are despatched on a first in first out (FIFO) basis, with each process in turn being given a limited amount of CPU time called a time slice or quantum and if the process does not complete before it time expires or before a higher priorty interrupt occurs, the despatcher gives the CPU to the next process
How does first come first served work?
Jobs are processed in the order in which they arrive, with no system of priotires
in round robin how does the scheduling generate interrupts at specific times?
The operating system sets an interrupting clock or interval timer
What does a round robin scheduling help guarantee?
Guarantee a reasonable response time to all users of the system
How does shortest remaining time scheduling work?
The smallest estimate time to completion is run next
What does shortest remaining time scheduling do?
Reduces the number of waiting jobs, and the number of small jobs waiting behind big jobs
What is a disadvantage of shortest remaining time scheduling?
requires knowledge of how long a job will take, so the user has to estimate the job time
How does shortest job first scheduling work?
The process of smallest estimated running time is run next
what is multi-level feedback queues scheduling designed to?
Give preference to short jobs, give preference to I/O bound processes and separates processes into categories based on their need for the processor
How does multi-level feedback queues scheduling work?
The algorithm implements several job queues and job can move between queues, depending on how much processor time they use
What is the aim of multi-level feedback queues scheduling?
Maximise processor use
What is the operating system required to store to know where files are stored so they can be quickly accessed?
A directory of files
What system, that comes with you desktop operating system, enables a user to moves files and folders, delete files and protect others from unauthorised access?
File management system
What is a buffer?
The data to be sent to an input or output device will then be transferred to an area of memory, so that the CPU can continue with another task
What is peripheral management?
The operating system needing to communicate with input or output systems which their are a lot of different types of
What is the purpose of a buffer?
To compensate for the difference in speed between the output device and the CPU
