The Lisa operating system features protected memory, enabled by a crude hardware circuit compared to the Sun-1 workstation (c. 1982), which features a full memory management unit. Motorola did not have an MMU (memory-management unit) for the 68000 ready in time, so third parties such as Apple had to come up with their own solutions. Despite the sluggishness of Apple's solution, which was also the result of a cost-cutting compromise, the Lisa system differed from the Macintosh system which had no protected memory until OS X, released eighteen years later. (Motorola's initial MMU also was disliked for its high cost and slow performance.) Based, in part, on elements from the Apple III SOS operating system released three years earlier, the Lisa's disk operating system also organizes its files in hierarchical directories, as do UNIX workstations of the time which were the main competition to Lisa in terms of price and hardware. Filesystem directories correspond to GUI folders, as with previous Xerox PARC computers from which the Lisa borrowed heavily. Unlike the first Macintosh, whose operating system could not utilize a hard disk in its first versions, the Lisa system was designed around a hard disk being present.