Data Center Electrical Power and Energy Management 133
Electrical power is generated, transmitted, and used as either alternat-
ing current (AC) or direct current (DC). Utility-provided electricity is AC.
Most commercial and consumer electronics operate on supplied AC power
that is converted to DC, if necessary, internally. For example, servers and
storage devices are supplied with AC power that is then converted to DC by
internal transformers. Items that operate off battery power either use DC
natively or require conversion using a DC-to-AC inverter. AC electrical
power voltages may be supplied as 120, 208, 240, or 480 volts, depending
on the type of service and number of phases (one, two, or three). Frequency
varies with location: North America ...