From then on, the system ran Monday morning to Friday afternoon, providing 60 hours of up-time for the users, but requiring 44 hours of scheduled downtime. Nevertheless, it was increasingly used as NASA programmers learned ways to get performance out of the complex system. At first, performance was dismal, with most programs running at about 15 MFLOPS, about three times the average for the CDC 7600. Over time this improved, notably after Ames programmers wrote their own version of FORTRAN, CFD, and learned how to parallel I/O into the limited PEMs. On problems that could be parallelized the machine was still the fastest in the world, outperforming the CDC 7600 by two to six times, and it is generally credited as the fastest machine in the world until 1981.