Intro

Question 1

What’s an abstract machine?

Answer 1

• Each app sees/gets its own “abstract machine”
  – There are multiple abstract machines, isolated from each other
  – So each app sees the system as if it was dedicated to itself,
  and it’s the job of the OS to juggles resources to support this illusion

Question 2

What are the 4 upsides of an abstract machine?

Answer 2

1. Better than the physical HW, because it allows the OS to
   – Hide physical restrictions, and
   – Support more convenient interfaces
2. Apps often don’t access physical resources directly
   – There’s a level of indirection
3. Making it possible to support e.g bigger virtual address space then there is physical memory.
4. It provides “portability”
   – The ability to correctly run the same exact program in different environments (in terms of source code, not necessarily binary code)

Question 3

What are the 3 different ways to view the OS?

Answer 3

1. By its programming interface
   – Its system calls
2. According to the services it provides
   – Time slicing (how multiprogramming is implemented), filesystems and their operations, etc.
3. According to its internals, algorithms, & data structures