Complex sentence: Lisp Machines ran the tests in parallel with the more conventional single instruction additions-if the simultaneous tests failed, then the result was discarded and recomputed; this meant in many cases an increase by several factors.
Split into simpler sentences: Lisp Machines ran the tests in parallel with the more conventional single instruction additions. If the simultaneous tests failed, then the result was discarded and recomputed; this meant in many cases an increase by several factors.