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15 Midplane: Description/Voltages
This chapter describes the midplane.
Warnings and Cautions
Only a qualified service technician is authorized to remove the server covers and to access any
of the components inside the server. Before removing the covers, see “Safety Guidelines” on
page 115.
Midplane Features
The midplane distributes the power load—CPU and PHP I/O baseboards, memory modules,
peripheral bays, and hot-swap hard disk backplane—among two or three 750 watt autoranging
power supplies. It also provides a bus interface for the CPU and PHP I/O baseboards, memory
modules, and the hot-swap hard disk backplane. The midplane provides the following voltages
and maximum currents:
Voltage Maximum Current
+12 V 56 A
+5 V 68 A
+3.3 V 61 A
5 V standby 1 A
-12 V 1 A
+24 V Bias 100 mA
I
2
C Bus
The private I
2
C bus monitors failures and voltage margining in the server. The 5 V standby
voltage provides power for the bus, and it is available even when the server power is off.