Operating Systems 2019W Lecture 1
Video
Video from the lecture given on January 7, 2019 is now available.
Notes
In class
Lecture 01
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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"?
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OS kernel
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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