The correct answer really is going to depend on brand and model of slide you have, I sat through a 2 day seminar on Lipert products much of which was on slide maintenance a few weeks ago, and in their products alone there are at least 3 styles of control systems for slide operation. Some use limit switches, some use current sensing limiting, and some use rotational counting on the motor shafts. Some have simple manual overrides, some don't, it really just depends on what type of slide you have.