Step 1: Why saturation slows a transistor down. In ordinary TTL-type switching, the transistor is driven hard into saturation when it turns ON. This means excess minority carriers pile up in the base region, and before the transistor can turn OFF again, all that extra stored charge must first be swept out. This clean-up time is called storage delay, and it is the biggest reason ordinary saturated logic is slow. Step 2: How ECL avoids this problem. Emitter Coupled Logic works on a completely different idea called current steering. A differential pair of transistors shares a constant current source, and instead of switching a transistor fully ON or OFF, the circuit simply steers the same current down one branch or the other. Because the transistors never leave the active region, they never accumulate that extra stored charge in the first place. Step 3: The result on switching speed. With no charge storage to remove, there is no storage delay, so the transistor can change state almost instantly whenever the input changes. This is exactly why ECL is the fastest of the common bipolar logic families. \[ \boxed{\text{the transistors are not saturated when conducting}} \]