=========
Processes
=========

States
======

Running
-------

Running on the processor.

Blocked
	Waiting for something.

Ready
	Waiting to be allocated CPU time.

State Transitions
=================

Running -> Ready
	Preempted by scheduler

Ready -> Running
	Scheduler selects process

Running -> Blocked
	Process waits for some event.

Blocked -> Ready
	IO finishes.

Process Control Block (PCB)
===========================

- A table containing information about each process.
- Contains enough information to re-start a process if it is stopped.

Context Switch
==============

The process of stopping one process, saving it's state to the PCB, loading the state of another process from the PCB, and running it.

Threads
=======

- Multiple flows of controll inside each process.
- Each thread has it's own PC, registers and stack.
- Threads in the same process share the same code, global variables and FDs.

User-Level Threads
------------------

This is where threads are implemented as a library in the process, so the OS only sees one process with one thread.

- Fast thread creation and scheduling.
- If one thread blocks, the entire process is blocked.
- Can't take advavtage of multiple processors.

Native/Kernel Threads
---------------------

Where threads are scheduled and managed by the kernel.

- Can take advantage of multiple CPUs.
- Slow to start because it involves a system call.