Soma at 01:51, 17 September 2026

2026-09-17T01:51:51Z

← Older revision		Revision as of 01:51, 17 September 2026
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	* [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02a-20260915.mp4 September 15th video]		* [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02a-20260915.mp4 September 15th video]
	* [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02b-20260916.mp4 September 16th video]		* [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02b-20260916.mp4 September 16th video]

			==Notes==


			<pre>
			Lecture 2B
			----------

			* We're not doing assigned TAs
			* Please try to go to your assigned tutorial, but you may go to any tutorial if needed
			- in general there is more room in the B tutorials
			* You have until Sept 22nd to get T1 done

			I'll be posting the list of TAs and their office hours by next week.


			Textbook
			- after today, go read (or at least skim) Chapter 1
			- contains much more than I'm covering, but is a good supplement

			Today we're starting with a historic approach

			It starts with Moore's law
			- number of transistors on a chip doubles every 2 years, so exponential growth

			exponential growth never continues forever
			- Moore's law is mostly done now?

			key ideas of operating systems were developed in the 1960's and 1970's

			We keep using them because
			- they work (sort of)
			- our software depends on those ideas

			Modern computing is full of illusions
			- we call them abstractions, but it goes further

			Examples
			- speculative execution
			- old CPUs executed one instruction at a time
			- most programming languages are built around this idea (mostly)
			- but modern CPUs are pipelined & superscalar
			- they execute more than one instruction at a time, even
			for sequential code
			- pipelining is just an assembly line applied to CPU instructions
			- because there are multiple stages to executing an instruction
			- speculative execution happens because of branches (if/then statements,
			while loops)

			Modern CPUs are so complicated that they have little operating systems in them!
			- used to set up all the hardware & other things

			I/O devices <-> CPU <-> RAM (volatile memory)

			How many programs would an Apple II run at a time?
			- only one!

			Modern operating systems have two key tasks:
			- resource management (managing sharing)
			- abstraction

			How much sharing are we talking about today?
			- many many programs
			- many users (sometimes)
			- THE NETWORK

			So in other words, the OS is abstracting and managing the resources provided by
			- the CPU, RAM, and I/O devices

			But how do we share these?
			- I/O devices: make programs take turns or share, abstract
			- keyboard: one at a time
			- screen: shared between windows (GUI)
			- disks: filesystems
			- CPU: take turns
			- RAM: everyone gets some RAM

			Most efficient path is to make all code cooperate
			- but if any behave badly, it all falls apart

			So how do we enforce proper sharing in the face of bugs or just misbehaved code?

			operating systems enforce resource sharing through raw power
			- they are the dictator of their systems, with absolute authority

			But operating systems are just code
			- how can some code rule over other code?

			Basically, the operating system runs first
			- because the hardware is waiting to be controlled when first started

			So what mechanisms does hardware have to facilitate managed sharing of resources?
			- Interrupts
			- virtual memory

			Virtual memory means that every address a program uses is a virtual address
			- has to be translated to a physical address on every memory access


			Applications
			-----------
			Kernel
			-----------
			Hardware


			With virtualization:

			Applications
			-----------
			Kernels
			-----------
			Hypervisor
			-----------
			Hardware
			</pre>

Soma: Created page with "==Video== Video from the lectures given on September 15th and 16th, 2026 are now available: * [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02a-20260915.mp4 September 15th video] * [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02b-20260916.mp4 September 16th video]"

2026-09-17T01:49:36Z

Created page with "==Video== Video from the lectures given on September 15th and 16th, 2026 are now available: * [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02a-20260915.mp4 September 15th video] * [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02b-20260916.mp4 September 16th video]"

New page

==Video==

Video from the lectures given on September 15th and 16th, 2026 are now available:
* [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02a-20260915.mp4 September 15th video]
* [https://homeostasis.scs.carleton.ca/~soma/os-2026f/lectures/comp3000-2026f-lec02b-20260916.mp4 September 16th video]

Operating Systems 2026F Lecture 2 - Revision history

Soma at 01:51, 17 September 2026