I/O Velocity Plot

SRM uses the I/O velocity plot to keep track of the relationship between the number of channel paths connected to a subsystem (along with the channel path's utilization) and the I/O velocity of that subsystem. There is one I/O velocity plot for each I/O subsystem (control unit).

If there is a single channel, the contention factor equals the channel utilization. If there are multiple channels, the contention factor is the utilization a single channel would have to have to be equivalent to the channels connected to the control unit, given the number of channels and their average utilization. In this case, “equivalent” means that an I/O operation would have the same probability of experiencing delay.

The I/O velocity plots are recorded in the subtype 9 records.