The VAX 4000 Model 105A enclosure uses a 460-watt power supply that consists of two regulators. Regulator "A" supplies power for slots 1, 3, 5, 7, 9, and 11 and mass-storage shelves 3, 4, and 5. Regulator "B" supplies power for slots 2, 4, 6, 8, 10 and 12 and mass-storage shelves 1 and 2. When configuring the BAl23 caster- mounted enclosure Use the 12-slot configuration template of VAX 4000 Model 105A for the system building blocks. Write the module and mass-storage device names in the left column beside the slot and shelf numbers. When configuring these systems, please note that quad-height modules use both the "AB" and "CD" portions of a slot. Slots 1 through 4 are limited to either one dual- or one quad-height Q-bus option. However, if an MS630-AA memory option for VAX 4000 Model 105A is installed in the "CD" row of slot two or three then the "AB" rows of that corresponding slot should remain open. Slots 5 through 12 can accommodate either two dual-height or one quad-height options. Enter the 5 V and 12 V currents, power, the ac and dc bus loads and I/O panel inserts required for each module and mass-storage device. Be sure that you enter the power for each option in the columns of the appropriate regulator. The col- umn totals must not exceed the limits listed at the bottom. Due to start-up current limitations in the VAX 4000 Model 105A power supply, if an RD54 disk drive is connected to the same 12 volt power supply regulator as another RD-type disk drive, then only five of the seven amperes provided by that regulator can be used for powering the two disks and any additional options.