"Audio Engine" is terminology frequently used by digital audio software companies to describe their software - eg "superior audio engine.....". Out of pure interests sake - what is this "audio engine"? Can one software app be better than another or does the software just make use of the applicable OS and sound card? Can anyone hear a difference?

What also puzzles me is some apps are 3MB and others 100MB or more - not taking loops, realtracks etc into account. Is this a function of the features in the program or just efficient programming?

Thanks for helping me to understand these observations.
Roy