The Node.js Event Loop: Not So Single Threaded

gistfile1.txt

https://www.youtube.com/watch?v=zphcsoSJMvM
1. single threaded process

2. co-operative multi tasking
    Application running on the operating system should yield the OS. 
    Once the application has yielded then the OS run the other tasks.
    This has a big flaw if the application doesn't yield, then the OS will wait for long time.

3. pre-emptive multi tasking 
    OS has the ability to pause the application and execute its commands.
    Which means that OS reloads the other application and runs it without knowing anything about the application.
    This means that OS is saving the current State of running application and reloads other application. This causes the applications are interleaved for processing. 
    This means that if the application crashes OS won't crash.

4. Symmetric Multi Threading
    Instructions in OS are executed in stages which are break into down into steps.
    Steps in the processor is called pipeline.

Task is same thing as process

Process Vs Threads

Process                                 Threads
--------------------------------------------------------------
Top level execution container           Runs inside process
Separate Memory Space                   Shared Memory Space
Communicate via IPC                     Pleathora of options available that depends on runtime

Node consists of JS, V8, chrome V8 and C++. 
When node code calls synchronous method it C++ runs in main thread.
When node code calls asynchronous method it C++ may run in main or other thread.