Process

Process is the abstraction for executing a program with limited privileges

• it needs permission from kernel to access the memory, disk, anything
• Process is Instance of program
  • ex. many process for same program
• Program = part of Process state
  • ex. program can invoke more than one process

Segments of Application

1. Code
   • instructions
2. Data
   • initialized global variables
3. Stack
   • Local varibles
   • arguments
4. Heap
   • dynamic allocation (malloc, free)

Exceptions handling

• some codes should be restricted, because of its potential danger.
  • Simple approach: run instruction in simulator (ex. JVM)
  • faster approach: run directly in CPU user mode, take exceptions to maintain safety
• Exceptions
  1. System calls = protected procedure call
     • intentional, request by program to OS
     • limited, carefully coded
  2. Interrupts (Async)
     • Timer, I/O
     • manage with interrupt vector table
  3. Exceptions (Sync)
     • div0, segfault, …

Two Components of process

1. Execution Thread
   • sequence of execution
   • single thread, no concurrency
2. Address Space
   • execution environment
   • CPU registers, main memory, IO, File system, …

Shell

Job Control System

• create, manage set of programs to do some task.

Process Control