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.)

Question

Quizplus · Accepted Answer

The Answer is Amount of time CPU takes to process each 64 KB block
= ((2 * 106)/ (3 * 109)) * 103
= 0.67 ms
Amount of time spent in memory transfer for 64 KB block
= ((64 * 210)/(640*220)) * 1000 = 0.097 ms
Amount of time spent in I/O transfer for a 64 KB block
= seek time + rotational delay + transfer time + controller overhead
= 9 + ((64*210)/(64*220))*103 + ((106 * 3)/109)*103
= 12.97 ms
The main bottleneck is I/O in the above system.

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