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
