OSC

Process 1

Memory Image

flowchart TD
    Process --> Code["Code (Text)"]
    Process --> Data
    Process --> Stack
    Process --> Heap

    Code --> MemoryImage[Memory Image]
    Data --> MemoryImage
    Stack --> MemoryImage
    Heap --> MemoryImage

• Process
• Memory Image

Process Control Block

flowchart LR
    ProcessId[Process Identification] --> PCB
    PCtrl[Process Control Information] --> PCB
    PState[Process State Information] --> PCB

    PCB --> ProcessTable[Process Table]

• Process Identification
• Process Control Information
• Process State Information
• Process Control Block (PCB)
• Process Table
• Process States

Process Status

flowchart TD

New(New)
Ready(Ready)
Running(Running)
Blocked(Blocked)
Terminated(Terminated)

    New-- Admit the process and commit to execution -->Ready
    Running-- Wait for input or syscall -->Blocked
    Ready-- Chosen by process scheduler -->Running
    Blocked-- Waited event finished -->Ready
    Running-- Surrender the processor -->Ready
    Running-- Finish or exception occurred -->Terminated

• New
• Ready
• Running
• Blocked
• Terminated
• Suspended

Interrupts and syscalls drive the transitions of process status.

Context Switching & Time Slices

The system saves the state of the old process and loads the state of the new process. (Overhead)

Time Slices

• Short
  • good response time
  • low effective
• Long
  • poor response time
  • better effective utilization

1. Save process registers
2. Update PCB (Running -> Ready / Blocked)
3. Move PCB to queue accordingly
4. Run scheduler to select next process
5. Update new PCB to Running state
6. Update memory manage unit (MMU)
7. Restore process