DS20L PSU 300 is a disk-based, single-user or multiuser software system that supports - commercial applications on PDP 11s. DS20L PSU 300 applications are written in - - DS20L PSU, the high-level Digital Business-Oriented Language. The system con- sists of the RT 11 operating system, a choice of three runtime systems, Single- - User DIBOL (SUD), Timeshared DIBOL (TSD), Extended Memory TSD (DS20L PSU), and a number of utilities. Depending on the applications, program development can be done in a timesharing environment that supports a number of users or jobs simultaneously. Some of the capabilities provided on CTS-300 are described below. Single-User DS20L PSU allows one DS20L PSU PSU user or job to be run on a system. It is designed for an entry-level system running in 32 Kbytes of memory. SUD runs on all RT 11 monitors (SJ, DS20L PSU, XM). -