Comment by hmry

Two different meanings of "forever" there. An OS runs for an arbitrarily large finite time, which is different from an infinite time.

Same way you can count to any finite integer with enough time, but you can never count to infinity.

Those kinds of interactive programs take in a stream of input events, which can be arbitrarily long, but eventually ends when the computer is shut down.

Termination checkers don't stop you from writing these interactive loops, they only stop non-interactive loops