The average seek time and rotational delay in a disk system are 6 ms and 3 ms, respectively. The rate of data transfer to or from the disk is 30 Mbytes/sec, and all disk accesses are for 8 Kbytes of data, stored in contiguous sectors. Data blocks are stored at random locations on the disk. The disk controller has an 8-Kbyte buffer. The disk controller, the processor, and the main memory are all attached to a single bus. The bus data width is 32 bits, and a single bus transfer to or from the main memory takes 10 nanoseconds.
(a) What is the maximum number of disk units that can be simultaneously transferring data to or from the main memory?
(b) What percentage of main memory accesses are used by one disk unit, on average, over a long period of time during which a sequence of independent 8-Kbyte transfers takes place?