Help me on Computer simulation course

What do you understand by independent and identically distributed (IID) random variables? in a manufacturing facility, parts arrive to a drilling center for processing. After processing, the parts leave the drilling center. If a part arrives and finds the drill press idle, its processing at the drilling center starts right away, otherwise it waits in a FIFO queue. Two students conducted simulation experiments with the system described student B doubled the arrival times in comparison to student A. the results of the simulation experiments are shown in Tables 1 and 2. for the data shown in Tables 1 and 2, compute the sample mean, sample standard deviation, and half widths of 95% confidence intervals on the expected performance measures Compare the performances of the systems as simulated by student's A and B