There's three kinds of control flow model, single threaded, virtual process and multithreaded process. this is what has designed in the energy point that we study form

Virtual processes. This is dependant on a single threaded model but provides the appearance of concurrent execution. a controller component agendas the execution from the other components and provides them control. The arranging can be carried out periodically or according to occasions. This model is dependant on a logical decomposition of activities in easy steps whose execution requires only short times of your time.

I could not comprehend it and could not comprehend the distinction between multithreading process and vice president. can someone help?

EDIT here the chapter from the book that we mention the section above form http://www.mediafire.com/?ru82i0nvp12qw6t

This term "virtual process" is unusual but according to your description I'm able to give 2 real-world good examples of utilizing each.

For multithreading, imagine you've got a large amount of data in memory and wish to carry out some information onto it... you are able to split that data up and also have seperate threads (1 per CPU core, ideally) concurrently focusing on different portions from the data. By doing this, the information is going to be done faster according to the number of threads you create.

For 'virtual process', imagine you have to retrieve 20 files from remote servers... the majority of the CPU 'work' involved with case hanging out awaiting bytes to reach in the remote network. Creating separate threads to download all these files wouldn't result in the files arrive any faster. Contrary, getting extra threads the OS must constantly switch between (and it'll switch a great deal because more often than not each thread will just say 'im still waiting' after which cede control). So, within this situation it's better to possess a single thread doing all the installing, cycling internally between each one of the download tasks to see incomming data from their buffers.

Your virtual process looks in my experience like event driven programming. Google for eg. 'threads vs events', the first link you receive is very fine comparison.

EDIT: Here's another comparison I have present in bookmarks.