Flashcards in 1.2.1 Systems Software Deck (32)
What is an operating system?
A program that manages the operations of the computer for the user in order to act as a bridge between the hardware and the user.
What are the six functions an operating system performs?
Providing a user interface
Management of all I/O.
What are the two memory management techniques?
Paging and segmentation.
How does paging work?
Memory is divided into "pages" of 4kb each, a program can be stored in several non-contiguous pages. A page table uses mapping to store the link between the physical and logical page locations.
How does segmentation work?
Memory is divided logically into segments according to its contents.
What is an interrupt?
A signal from software, hardware, internal clock or peripherals.
Why does a software interrupt happen?
When an application terminates or requests certain services from the OS.
Why might a hardware interrupt happen?
A hardware interrupt will occur when an I/O operation is complete or an error arises.
If there are no errors and nothing being completed or terminated why might an interrupt still take place?
Interrupts are triggered regularly by a timer in order to interrupt a process to allow the next process to have processor time.
What happens when the CPU receives an interrupt?
The CPU suspends the current process and disables all interrupts of a lower priority. it then clears the program counter and all other registers by sending their values into the system stack. and the appropriate ISR is called to deal with the issue.
What is an example of a high priority interrupt?
What is an example of a low priority interrupt?
I/O operation termination.
When does the test for interrupt presence occur in the fetch decode execute cycle?
at the end, if the presence is detected then control is transferred to the appropriate ISR.
What does multitasking mean?
A single processor computer carrying out small parts of multiple larger tasks to give the appearance of simultaneous processing.
What are the objectives of the scheduler?
Be fair to all users
Provide acceptable response time for users
Ensure hardware is in as much use as possible.
What are the five scheduling algorithms?
RR - Round robin
FCFS - First come first serve
SJF - Shortest job first
SRT - Shortest remaining time
Multilevel feedback queues.
How does RR work?
Processors are dispatched in a first in first out basis, each process is given the same time slice with the processor, regardless whether the process has been completed or not, the next process will be given its time slice, this continues until the processes have been finished.
How does FCFS work?
Jobs are processed in the order in which they arrive in their entirety.
How does SJF work?
The process with the smallest estimated time is run next.
How does SRT work?
The process with the smallest estimated time is run next since that will always be the one currently executing processes will be completed in full.
How do multilevel feedback queues work?
The algorithm implements multiple queues all with their own scheduling algorithm and each queue is organised based on priority.
What are the five types of OS?
What is a distributed OS?
A form of parallel processing which spreads a workload over multiple servers but appears to the user as if it were a single system handling the workload.
What is a real-time OS?
An operating system designed to give a response within a guaranteed time frame
What is an embedded OS?
An OS with a minimal user interface used to control devices based on input from sensors.
What is a multitasking OS?
An OS that allows the user to run multiple programs at once and can switch between them to give the appearance only one is running.
What does BIOS stand for?
Basic Input Output System.
Where is the BIOS stored?
What is the purpose of the BIOS?
To initialise the PC and to test the system hardware as well as to load the operating system from the hard disk to RAM.