Virtualization

a technology that allows multiple OSs and Apps to run on a single physical server or hardware.

Process Management

• Process
• Thread
  • Single-threaded: one program counter
  • Multi-threaded: one program counter per thread

Interrupt driven

• Hardware interrupt: some devices (e.g. keyboard)
• Software interrupt
  • exception: invalid memory access, division by zero
  • trap (system call): Request from a specific program for an OS service
  • Breakpoint: Pause the execution of a program at a specific point for debugging purposes

Dual mode

Mode register: store bit which tells what mode the system is running

• User mode: 1
• kernel mode: 0

Return from exception

A single hardware instruction:

• Swaps the PC and the PC'
• Sets the mode bit to user mode