The combination of hardware and software to be used for the library system provides an average direct access time of 20 msecs. The system specification states that a Loan transaction should be...

The combination of hardware and software to be used for the library system provides an average direct access time of 20 msecs. The system specification states that a Loan transaction should be processed within 0.5 seconds, 95 per cent of the time, even if five Loan transactions arrive simultaneously from different library counter terminals. An active borrower has, on average, three books on loan when a further loan is requested. No borrower has more than ten books on loan. On average a borrower borrows two books at the same time. Compare the merits of the first- and second-level designs (Figs 14.2, 15.2).