Question about spawn percentages??

[Gel Mibson]

Sorry for the noob question.

When the wiki says a mob such as Ancient Cyclops has a 1% chance to spawn, does the game code perform a "/random 1 100" to determine if he will spawn?

So lets say to spawn an Ancient Cyclops the winning number is "7". If the dice hits before he spawns, then profit?

Is it that simple or is it something entirely different?