The elapsed time to retrieve a required page varies considerably depending on where it is coming from.

These elapsed times for the 3380 and 3390 are quite generous and more closely approximate upper acceptable limits rather than the optimal times that are 20 and 16 Ms respectively.

Most installations still have poor overall DASD performance that impacts the online applications. Some of the primary causes are lack of staff time to properly place objects to reduce contention, and the ever larger capacity devices...so there are fewer physical devices to spread the objects and I/O workload across.