“ARGOS” (ARGonne Operating System), which runs on a Xerox Sigma 5 hardware configuration, provides a dynamic multiprogrammed environment which supports the following: data acquisition and interactive control for numerous (currently 19) independently running on-line laboratory experiments; three interactive graphics terminals; FORTRAN IV-H executing at each of 23 remote time-shared terminals; a jobstream from open-shop batch processing; long-term low priority computations (100 CPU hours). The system guarantees the protection of each user's interests by the utilization of the hardware memory-protection feature, internal clocks and disallowing the execution of privileged instructions by user programs. The system is interrupt-driven, with each task running to completion, contingent on its priority. System resources are provided on a first come first served basis, except that rotating memory is queued by request position. System CALLs provide users full access to hardware capability, thus providing user-directed file formats and insuring a minimum of system overhead. However, at some sacrifice in overhead, the user can make use of FORTRAN record-blocking. Core memory, disk space and magnetic tape usage, are assigned dynamically. Parametrization of the system is such that terminal characteristics are specified (one parameter card/terminal) at boot-in time (once/week after preventive maintenance).