Operating Systems 2019W Lecture 1
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Video from the lecture given on January 7, 2019 is now available.
Lecture 01 ---------- What is an operating system? * resource management * abstraction Software that turns the computer you have into the system you want to program Linux - operating system "kernel" "GNU/Linux" - because an OS is a kernel + other stuff, and GNU made a lot of the other stuff Security Threat model - every defense has limits - threat models capture the kinds of attacks a defense defends against Problem models - what problem are you trying to solve? - what are you assuming about the world? What happens when a program crashes? - program "misbehaves" and is shut down MS-DOS et al - "operating systems", but not modern operating systems - yes: abstracts disk access - no: no support for running multiple programs safely - TSRs like sidekick allowed "multiple" programs to run at once (actually, allowed you to switch programs, in a hack-y way) Modern computers must multitask, because they have to deal with - user input/output - network input/output Someone has to be in charge on a modern operating system - allocate resources - deal with misbehaving programs The operating system kernel is what does the above The kernel runs first, so it gets the "high ground" - it gets first access to the hardware - hardware distinguishes between what is first run and the rest - hardware has "modes" for running different kinds of code How safe is it to depend on the "who came first"? F | E | i | m | r | a | e | c | f | s | o | | x | | ------------ OS kernel ------------ hardware running program on a modern OS: process requests from a process to the kernel: system calls system calls often look like function calls When you make a function call, the CPU jumps to the address of the function called (and arguments + return address are pushed on the stack) System calls require you to jump to a new address space and change CPU modes