What Is the Bottleneck in the Following System Setup, the CPU

Essay

What is the bottleneck in the following system setup, the CPU, memory bus, or the disk set?
$\bullet$ The user program continuously performs reads of 64KB blocks, and requires 2 million cycles to process each block.
$\bullet$ The operating system requires 1 million cycles of overhead for each I/O operation.
$\bullet$ The clock rate is 3GHz.
$\bullet$ The maximum sustained transfer rate of the memory bus is 640MB/sec
$\bullet$ The read/write bandwidth of the disk controller and the disk drives is 64MB/sec, disk average seek plus rotational latency is 9ms.
$\bullet$ There are 20 disks attached to the bus each with its own controller. (Assume that each disk can be controlled independently and ignore disk conflicts.)