Available power for the mainframe is the maximum power available for mainframe usage including fans, backplane, monitor and display circuits (standard and option 1M), and slots 0 - 12 usage. Usable power (power used by the modules in slots 0 -12) is equal to the available power minus the mainframe usage.  Test system integrators are mostly concerned about the useable power ratings listed below.   Chassis Maximum Available power (W) Maximum Usable power (W) VX1411A 750 700 VX1410A 925 875 VX1420A 1000 875