HTML Java script MYSQL programmers dev..(elmo)

I got an exam question and didn't know answer.
The task was:

----------

A programmer would like to create a very fast application, hence it organizes its software in 13 processes (a parent and 12 children), all running in parallel. <br/>
Child threads are very :

 1. I/O-intensive, hence make very frequent use of system calls (read/write from files/pipes/sockets, write on standard output, etc.)
 2. CPU intensive, hence make very frequent use of system calls: <br/>

Describe when this would be a good choice, when this would be a bad choice, and motivate your answer.

----
Number 1 and 2, are different questions. So answer should be for both. Good and bad sides of I/O intensive, good and bad sides of CPU intensive. <br/>
* Sorry for inappropriate topic, I changed it. <br/>
* "Child Threads" was on exam paper. So I copied it. I think, my professor wanted to write "process"

----
Thank you