Response time is actually comprised of the following criteria:
I/O service time: Total time to perform physical reads and writes to disk.
I/O queueing delay: Total time waiting to perform physical reads and writes to disk.
CPU service time: Total time to service a process. e.g. data sorting, logical I/O.
CPU queueing delay: Total time waiting for CPU service.
Physical I/O (i.e. disk) is always slower than logical I/O (i.e. memory).
Therefore disk related time is a significant response time component.
Note: Other components exist from the user perspective. e.g. network delay, delays in the client workstation. For simplicity, examination of response time will be from the database perspective, and row locks will be ignored.
response time = I/O service time + I/O queueing delay + CPU service time + CPU queueing delay