The sophistication of the Lisa software (which included a multitasking GUI requiring a hard disk), coupled with the slow speed of the CPU, RAM, lack of hardware graphics acceleration co-processor, and protected memory implementation, led to the impression that the Lisa system was very slow. However, a productivity study done in 1984 rated the Lisa above the IBM PC and Macintosh, perhaps countering the high degree of focus on UI snappiness and other factors in perceived speed rather than actual productivity speed.