We propose a set of scheduling procedures for dealing with the sporadic task scheduling in a dynamic periodic system. For this we mean a system in which periodic tasks change their parameters dynamically (at run-time), in an unpredictable way. So, the off-line periodic task set will be different from the current periodic task set. It means that the task schedulability tests in such systems have to be made on-line. On the other hand, on-line evaluations in hard real-time systems must be done in a fast way, once the overhead incurred in these evaluations may jeopardize the tasks timing requirements. As it is common that exact tests, providing necessary and sufficient conditions for validating the schedule, are intractable algorithms (EXPTIME), they can not support on-line decisions. Then, our goal is to provide a sufficient condition for on-line scheduling tests which is fast (PTIME) and can be reasonably useful compared to the exact condition. We present a series of simulation runs that confirm the usefulness of our approach. © 1994 IEEE. 186191Baruah, S.K., Mok, A.K., Rosier, L.E., Preemptive scheduling Hard-Real-Time Sporadic Tasks on One Processor (1990) Proc. 11st IEEE Real-Time Systems Symposium, Orlando, FA, pp. 182-190Baruah, S.K., Rosier, L.E., Howell, R.R., Algorithms and Complexity Concerning the Preemptive Scheduling of Periodic, Real-Time Tasks on One Processor (1991) Real-Time Systems JournalCarlow, G.D., Architecture of the Space Shuttle Primary Avionics Software System (1984) Communications of the ACM, 27 (9), pp. 926-936Chetto, H., Chetto, M., Some Results on the Earliest Deadline Algorithm (1989) IEEE Transactions on Software Engineering, 15 (10), pp. 1269-1280Kuo, T.W., Mok, A.K., Load Adjustment in Adaptive Real-Time Systems (1991) Proc. 12th IEEE Real-Time Systems Symposium, San Antonio, TXLeung, J., Merril, M., A note on the preemptive scheduling of periodic, real-time tasks (1980) Information Processing Letters, 11, pp. 115-118Liu, C.L., Layland, J.W., Scheduling Multiprogramming in hard real-time environment (1973) Journal of the ACM, 20 (1), pp. 46-61Mok, A.K., (1983) Fundamental Design Problems for Hard Real-Time Environment, , PhD Dissertation, Dept. of Electrical Eng. and Computer Science,MIT, Cambridge, MASchwan, K., Zhou, H., Dynamic Scheduling of Hard Real-Time Tasks and Real-Time Threads (1992) IEEE Transactions on Software Engineering, 18 (8), pp. 736-748Sheppard, T., Gagne, M., A Model of the F18 Mission Computer Software for Pre-Run-Time Scheduling (1990) Proc. 10th IEEE Int. Conf. on Distributed Computing Systems, pp. 62-69Xu, J., Parnas, D.L., On Satisfying Constraints in Hard-Real-Time Systems (1991) Software Engineering Notes, 16 (5), pp. 132-145