19. A computer center has two identical computers for batch processing. The computers are used as parallel processors. Job times are estimated by the user, but experience has shown that an exponential distribution gives an accurate description of the actual job times. Suppose that at a point in time there are eight jobs remaining to be processed with the following expected job times (expressed in minutes):

Job 1 2 3 4 5 6 a 8 Expected time 4 8 | 50 1 30 20 6

a. In what sequence should the jobs be processed in order to minimize the expected completion time of all eight jobs (1.e., the makespan)?

b. Assume that computer A is occupied with a job that has exactly two minutes of processing time remaining and computer B is idle. If job times are deterministic, show the start and end times of each job on each computer using the sequence derived in part (a).