Hi, I want ask something about digital machine design:

Hi,I want ask something about digital machine design:The major steps in system design could be categorized as Behavioral Modeling, Pre-synthesis Simulation, Model and Equivalence Checking, and Post-fabrication Testing. And what's the unique features of these, and what are the software tools could be used for each categorize. Are all of these steps necessary for any IC design, say CPU, ASIC, ALU etc.?