ibm z's pr/sm and hardware attributes allow compute resources to be dynamically changed to meet workload demands. cpu and memory resources can be non-disruptively added to the system and dynamically assigned, recognized, and used by lpars. i/o resources such as ip and san ports can also be added dynamically. they are virtualized and shared across all lpars. the hardware component that provides this capability is called the channel subsystem. each lpar can be configured to either "see" or "not see" the virtualized i/o ports to establish desired "shareness" or isolation. this virtualization capability allows significant reduction in i/o resources because of its ability to share them and drive up utilization.