Operating Systems 2015F Lecture 2 - Revision history

Soma at 21:38, 8 September 2015

2015-09-08T21:38:06Z

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	==Video==		==Video==

			The video for this lecture [http://homeostasis.scs.carleton.ca/~soma/os-2015f/lectures/comp3000-2015f-lec02-09Sep2015.mp4 is now available]. Note that this lecture was pre-recorded.
	==Notes==		==Notes==

2015-09-08T12:25:19Z

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	* executes a special CPU instruction (software interrupt)		* executes a special CPU instruction (software interrupt)
	* cannot be done outside of assembly language without special support from the compiler		* cannot be done outside of assembly language without special support from the compiler

			Concepts that I think are unclear:
			* mounting
			* strace
			* system calls

2015-09-08T12:08:43Z

Notes

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	[[File:Call-flow-process.svg]]		[[File:Call-flow-process.svg]]


			'''Key Questions:'''

			* What is a system call, really?
			* How are programs separated from each other?
			* What is this "scheduler" anyway?

			System calls are the interface between a process and the operating system kernel. They are like function calls, but they are not function calls (although they may be wrapped in library function calls).

			Classic system calls:
			* files: open, read, write, close
			* process control: fork, execve, exit
			* memory: sbrk
			* networking (socket calls)


			Key idea: CPU privilege levels
			* applications run in "user mode", lowest level of privileges
			** no direct access to I/O devices
			** no ability to change amount of RAM
			** cannot control how often it has the CPU

			* Operating system runs at higher privilege
			** gets privileges because it runs first (at boot)
			** specifically, the OS kernel runs in "supervisor mode"
			** can control CPU, RAM, and I/O devices
			** kernel maintains control by setting interrupt registers (will explain more later)

			So why isn't a system call a function call?
			* function calls involve references to specific memory locations
			* processes cannot directly see kernel memory

			So what does an application do instead to make a system call?
			* executes a special CPU instruction (software interrupt)
			* cannot be done outside of assembly language without special support from the compiler

2015-09-08T11:31:09Z

Notes

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	==Notes==		==Notes==

	~~Figures referred to in the lecture~~:		Very abstract view of a computer:

			[[File:Abstract-computer.svg]]

2015-09-08T11:29:53Z

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	==Notes==		==Notes==

	[[File:~~call~~-flow-process.svg]]		Figures referred to in the lecture:




			Flow of control for a system call:

			[[File:Call-flow-process.svg]]

2015-09-08T11:12:57Z

Notes

2015-09-08T11:11:22Z

Notes

2015-09-08T10:58:32Z

Created page with "==Video== ==Notes=="

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==Video==

==Notes==