Legacy Glossary

This is a glossary of older terms. While many of the definitions are unchanged, some of the definitions may be out of date and some of the terms may no longer be in use in the Data Center industry. This legacy glossary provides definitions for hundreds of information and communications technology (ICT) and data center terms and acronyms. Arranged alphabetically and searchable, the glossary explains common industry vocabulary.
1 A B C D E F G H I K L M N O P R S T U V W Z

The property of a computer program, or program segment, that allows for the parallel execution of parts of the same program. Parallel programming covers a wide range of degrees, from the very small grain (e.g., similar operations on multiple elements of the same array or matrix) to large grain (e.g., simultaneous execution of unrelated procedures)

Pascal (PA)

A unit of pressure equal to one newton per square meter. As a unit of sound pressure, one pascal corresponds to a sound pressure level of 94

Patch Cord

Flexible cable unit or element with connector(s) used to establish connections on a patch panel (from ISO/IEC 11801: 1995)

Patch Panel

A cross-connect designed to accommodate the use of patch cords. It facilitates administration for moves and changes (from ISO/IEC 11801: 1995)


A mechanism for full duplex flow control (see IEEE 802.3, Annex 3_1B)


For SPEC's purposes, a peak configuration is one where the configuration is tuned especially to get the best result for a single, specific workload. Typically, this demonstrates the highest performance levels achievable. Peak is often used in combination with baseline configurations

Perforated Floor Tile

A tile as part of a raised-floor system that is engineered to provide airflow from the cavity underneath the floor to the space. Tiles may be with or without volume dampers

Performance Neutral

Performance neutral means that there is no significant difference in performance. For example, a performance neutral source code change would be one which would not have any significant impact on the performance as measured by the benchmark

Personal Digital Assistant (PDA)

A hand-held computer or personal organizer device

Physical Layer Entity (PHY)

Within IEEE 802.3, the portion of the physical layer between the medium mependent interface (MDI) and the media independent interface (MII), gigabit media independent interface (GMII), or 10 gigabit media independent interface (XGMII) consisting of the physical coding sublayer (PCS), the physical medium attachment (PMA), and if present, the WAN interface sublayer (WIS) and physical medium dependent (PMD) sublayers. The PHY contains the functions that transmit, receive, and manage the encoded signals that are impressed on and recovered from the physical medium (for example, see IEEE 802.3, Clauses 23-26, Clause 32, Clause 36, Clause 40, Clauses 48-54, Clauses 58-63, Clause 65, and Clause 66)


A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system (NFPA definition)

Point of Presence (PoP)

A place where communication services are available to subscribers. Internet service providers have one or more PoPs within their service area that local users dial into. This may be co-located at a carrier's central office


Portability flags or changes are those which are necessary for the correct execution of a benchmark. That is, the benchmark will not run or will produce the wrong output without these flags or changes


In computer terms, portable means that the code in question can be easily taken to a different system and made to work there. Code that is dependant upon quirks or specific resources of a certain system is usually considered not to be portable because of the difficulties in finding means of supporting these dependencies on the new system. The use of standardized definitions and interfaces, e.g., ANSI-C and POSIX, greatly aids portability because the difficult dependencies are hidden behind the standardized interfaces and the difficulties are shifted from the programmer to the system provider


Time rate of doing work usually expressed in horsepower or watts

Power Bus (or Electrical Bus)

See bus, power

Power Distribution Unit (PDU)

The junction point between the UPS and the cabinets containing equipment

Power Usage Effectiveness (PUE)

Globally accepted metric that is described by The Green Grid in several whitepapers. PUE illustrates the total energy used by a data center divided by the energy used by ICT equipment in that data center

Printed Circuit Board (PCB)

Board that contains layers of circuitry used for interconnecting the other components


See central processing unit (CPU)

Psychrometric Chart

A graph of the properties (temperature, relative humidity, etc.) of air. It is used to determine how these properties vary as the amount of moisture (water vapor) in the air changes


Machine for imparting energy to a fluid, causing it to do work
* Centrifugal pump: Pump having a stationary element (casing) and a rotary element (impeller) fitted with vanes or blades arranged in a circular pattern around an inlet opening at the center. The casing surrounds the impeller and usually has the form of a scroll or volute
* Diaphragm pump: Type of pump in which water is drawn in and forced out of one or more chambers by a flexible diaphragm. Check valves let water into and out of each chamber
* Positive displacement pump: Has an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. Examples of positive displacement pumps include reciprocating pumps and rotary pumps
* Reciprocating pump: A back-and-forth motion of pistons inside of cylinders provides the flow of fluid. Reciprocating pumps, like rotary pumps, operate on the positive principle. That is each stroke delivers a definite volume of liquid to the system
* Rotary pump: Pumps that deliver a constant volume of liquid regardless of the pressure they encounter. A constant volume is pumped with each rotation of the shaft and this type of pump is frequently used as a priming pump