I know that a PC can have multiple network adapters each of which with different network identifiers (IP,MAC etc.). 

My question is, can a certain PC have more than one active default gateway? And if so, how does the PC (or better say the OS) knows to what adapter use for any given packet?


Question: Why not have the gears inside the bottom bracket?
Answer: There actually is a 18-Speed IG drive that is on the market: the pinion drive.

Only a few framebuilders incorporate this in their frames, but they do exist...