本文是我在上UCSD的 CSE 120: Principles of Operating Systems (Winter 2020) 整理的笔记，第一课主要介绍了操作系统以及进程的一些基本概念。

1. Definition

   • Abstraction of a running program (dynamic)
   • While program is just static code

2. Resources

   • CPU
     • Processing cycles (CPU time)
     • Execute intstructions
   • Memory
     • Bytes or words
     • maintain state
   • Other resources (I/O)

3. Context of a Process (machine and kernel-related state)

   • CPU context
     • PC (program counter)
     • SP (stack pointer)
     • FP (frame pointer)
     • GP (general pointer)
   • Memory context
     • program code
     • static variables(init, uninit)
     • heap
     • shared memory
     • stack of activation records
   • Other (kernel-related state, …)

4. Process memory structure

   • Text area: code (program instruction)
   • Data
     • Global variable
     • Static variable (local and global)
     • Heap
   • Stack
     • Activation records
     • Automatic growth/shrinkage

5. Process stack

   • Stack of activation records
   • An activation records stores:
     • return address
     • link to previous record
     • local varibale
     • other
   • Stack pointer points to top

6. Multi-Processes

   • Goal: support several processes running “simultaneously” or let one process intentionally yield to another process
   • Method: Context switching
     • Switch process A (running) to process B (waiting) while store context (state) of process A (since it’s not finished)
     • process
       • save context of current process
         • save GP
         • save SP
         • save PC
       • load context of next process
         • load GP
         • load SP
         • load PC (must be last, once PC is loaded, the process B begins to run (PC indicates instruction execution))