Effective utilization of IBM 3090 large virtual storage in the numerically intensive computations of ab initio molecular orbitals

A new level of storage hierarchy, called Expanded Storage and available on the IBM 3090 system, is utilized by the MVS/XA™ operating system as high-speed paging equipment, allowing a user to hold application data in large virtual storage. To exploit the large virtual storage capability of the IBM 3090, a new application technique was developed for numerically intensive computations of inline ab initio off molecular orbitals where high-speed transfer of a vast amount of intermediate data is a common requirement of most application programs. An application program running under MVS/XA was modified so that it could handle a vast amount of intermediate data in large virtual storage combined with Expanded Storage, achieving a 4- to 10-fold improvement in turnaround time at a CPU rate-determining step (SCF step) in medium-sized molecules.