HP rp7440 Installation Guide, Fourth Edition - HP Integrity rx7640 and HP 9000 - Page 18

board can be selectively powered off for adding processors, memory, or for maintenance of the cell board, without affecting the other cell board in a configured partition. Figure 1-7 Cell Board The server has a 48 V distributed power system and receives the 48 V power from the system backplane board. The cell board contains DC-to-DC converters to generate the required voltage rails. The DC-to-DC converters on the cell board do not provide N+1 redundancy. The cell board contains the following major buses: • Two front side buses (FSB), each with up to two processors • Four memory buses (one going to each memory quad) • Incoming and outgoing I/O bus that goes off board to an SBA chip • Incoming and outgoing crossbar bus that goes off board to the other cell board • PDH bus that goes to the PDH and microcontroller circuitry All of these buses come together at the CC chip. Because of space limitations on the cell board, the PDH and microcontroller circuitry resides on a riser board that plugs into the cell board at a right angle. The cell board also includes clock circuits, test circuits, and de-coupling capacitors. PDH Riser Board The PDH riser board is a small card that plugs into the cell board at a right angle. The PDH riser interface contains the following components: • Microprocessor memory interface microcircuit • Hardware including the processor dependant code (PDH) flash memory • Manageability microcontroller with associated circuitry The PDH obtains cell board configuration information from cell board signals and from the cell board local power module (LPM). 18 HP Integrity rx7640 Server and HP 9000 rp7440 Server Overview