The use of the slowest-clocked version of Motorola's 68000 was a cost-cutting measure, as the 68000 was initially expensive. By the time the price had come down, Apple had already designed the Lisa software around the timing of the 5 MHz processor. Lisa had been in development for such a long time that it was not initially developed for the 68000 and much of its development was done on a pre-chip form of the 68000, which was much slower than the shipping CPU.