SITL vs HITL

SITL and HITL are two ways of testing control software before trusting it with real hardware. Software-in-the-loop (SITL) runs your actual code on an ordinary computer, connected to a simulator that pretends to be the vehicle and its sensors, so you can crash a thousand virtual drones for free. Hardware-in-the-loop (HITL) runs the code on the real flight board, but still feeds it simulated sensor data, which catches problems a laptop hides: timing, limited memory, driver bugs. Neither replaces real-world testing, since a simulator is only as good as its model of reality, but together they catch most mistakes cheaply and safely.