NonStop S-Series System Expansion and Reduction Guide

Glossary
G-Series Common Glossary
Glossary-77
POSIX
POSIX. The Portable Operating System Interface, as defined by the Institute of Electrical
and Electronics Engineers (IEEE) and the American National Standards Institute
(ANSI). Each POSIX interface is separately defined in a numbered ANSI/IEEE
standard or draft standard. The application program interface (API), known as
POSIX.1, has become ISO/IEC IS 9945-1:1990.
power distribution panel (PDP). A group of panel assemblies that composes a single
panel that includes buses and overcurrent protection devices (with or without
switches). A PDP is used for the control of power circuits.
power distribution unit (PDU). An assembly of outlets and fuses that can be installed on
both sides of a modular cabinet. This assembly provides power and over-current
protection for the components installed in the modular cabinet. See also computer-
room power center (CRPC).
power domain. A set of customer-replaceable units (CRUs) and field-replaceable units
(FRUs) that share a set of power rails. For telco Central Office (CO) systems, the
power domain is the entire system.
power factor. The ratio of real power to apparent power (that is, kilowatts/kilovoltamperes).
The power factor for a sinusoidal load is determined by the position of the applied
voltage waveform with respect to the current drawn by the load. When voltage and
current are in phase with each other, the power factor is unity, and the power for the
load is equal to the product of the applied voltage and load current (P=EI). When the
current waveform lags the voltage waveform, the load is inductive. Conversely, when
the current waveform leads the voltage waveform, the load is capacitive. In either case,
the power for the load is equal to the product of the applied voltage, load current, and
the angular displacement between the voltage and current waveforms (P=EIcosf).
Nonlinear (nonsinusoidal) loads also have a power factor. However, the power factor
for a nonsinusoidal load reflects harmonic content and not angular displacement.
power factor correction. The addition of a reactive component to offset the angular
displacement of a sinusoidal load. Traditionally, the normal power factor for a facility is
inductive, so the normal correction involves the addition of capacitors to offset the
lagging power factor. The capacitors offset part or all of the inductive reactance,
making the total circuit more nearly in phase with the applied voltage. The power factor
for nonlinear (nonsinusoidal) loads cannot be corrected through the addition of simple
reactive components. Harmonic filters are required to correct the power factor of
nonlinear loads.
power interface board (PIB). In system enclosures with power shelves, a board mounted
on the bulkhead located behind the power supplies in the power shelf. The PIB
provides electrical connection between the power supplies and DC power cables.
power monitor and control unit (PMCU). A field-replaceable unit (FRU) that connects the
batteries to the DC power distribution bus in an HP NonStop™ S-series enclosure and
provides a means of disconnecting the batteries for powering off the system. The
PMCU also provides a means for the service processor (SP) to diagnose the condition