12/04/2022, 09:17 Exam/OS Overview – COMP3231/COMP9201/COMP3891/COMP9283
Operating Systems Introduction
Describe the two general roles of an operating system, and elaborate why these roles are important.
Operating systems provide:
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Provide an abstract machine
Provides a standardised abstraction between hardware and userspace software that allows userspace software to be written with little concern for the hardware it is running on. Hides details of hardware to make application code portable.
Extends basic hardware with added functionality, such as higher levels of abstract of memory, files, screens, I/O etc
Provides common core for all applications, making it easier to program for Facilitates communication between I/O and userspace software.
Prevents applications from interfering with each other
Resource allocation to arbitrate between competing users/processes/threads Divides resources amongst competing programs or users according to some system policy to ensure fairness, isolation, and efficiency
Resources include files, memory, cpu runtime, etc.. Enforces resource allocation policies
Not a role: Privileged component of computer
What is the difference between user and privilege modes? Why do both exist?
In user-mode, there is a subset of instructions that can’t be used, in order to prevent applications from performing commands that are critical to the functionality of the OS / other applications (eg removal of interrupts). There is also a subset of usable memory in user-mode, as the kernel does not trust applications not to corrupt their own memory and can run privately with its own stack. The two modes of operation are required to ensure applications (from user- mode) does not bypass, circumvent, or take control of the OS.
Exam/OS Overview (last edited 2019-05-13 08:58:36 by KevinElphinstone)
https://wiki.cse.unsw.edu.au/cs3231cgi/Exam/OS Overview
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