[en] In the report the authors have presented a job scheduler for determination of optimal degrees of multiprogramming and prediction of processing time for a given set of jobs. It is assumed that the jobs' computational times and input/output frequencies are known beforehand. The jobs are sorted by the scheduler according to a LPT rule before scheduling. A Poisson arrival and a constant service time are assumed with each job's input/output operation. A modified round-robin algorithm is used to schedule a given set of jobs. A computational result of the scheduler is validated by a simulator which resembles closely with round-robin type operating systems. The scheduler is useful for automatic control of computer systems and the simulator is useful for simulations of existing operating systems. Both the scheduler and the simulator are written in Fortran language. (author)