Glossary

The Green Grid 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
Rack (from ASHRAE)

Frame for housing electronic equipment

Rack (from ASHRAE, industry)

Structure for housing electronic equipment. Differing definitions exist between the computing industry and the telecommunications industry
* Computing industry: A rack is an enclosed cabinet housing computer equipment. The front and back panels may be solid, perforated, or open depending on the cooling requirements of the equipment within
* Telecommunications industry: A rack is a framework consisting of two vertical posts mounted to the floor and a series of open shelves upon which electronic equipment is placed. Typically, there are no enclosed panels on any side of the rack

Rack Power

Used to denote the total amount of electrical power being delivered to electronic equipment within a given rack. Often expressed in kilowatts (kW), this is often incorrectly equated to be the heat dissipation from the electrical components of the rack

Rack, Air- and Liquid-cooled

Rack that requires both air and liquid provided by the building

Rack, Air-cooled

System conditioned by removal of heat only using air

Rack, Liquid-cooled

A liquid-cooled rack that accepts conditioned coolant; system conditioned by removal of heat using a liquid

Rack-mounted Equipment

Equipment that is to be mounted in an EIA (Electronic Industry Alliance) or similar cabinet. These systems are generally specified in EIA units, such as 1U, 2U, 3U, etc., where 1U = 1.75 inches (44 mm)

Raised Floor (from ASHRAE)

A platform with removable panels where equipment is installed with the intervening space between it and the main building floor used to house the interconnecting cables, which at times is used as a means for supplying conditioned air to the information technology equipment and the room

Raised Floor (from ASHRAE, industry)

Also known as access floor. Raised floors are a building system that utilizes pedestals and floor panels to create a cavity between the building floor slab and the finished floor where equipment and furnishings are located. The cavity can be used as an air distribution plenum to provide conditioned air throughout the raised floor area. The cavity can also be used for routing of power/data cabling infrastructure

Random Access Memory (RAM)

A configuration of memory cells that hold data for processing by a computer's processor. The term random derives from the fact that the processor can retrieve data from any individual location, or address, within RAM

Rated Current

The rated current is the absolute maximum current that is required by the unit from an electrical branch circuit

Rated Frequency

The supply frequency as declared by the manufacturer

Rated Frequency Range

The supply frequency range as declared by the manufacturer expressed by its lower and upper rated frequencies

Rated Voltage

The supply voltage as declared by the manufacturer

Rated Voltage Range

The supply voltage range as declared by the manufacturer

RC-class

Room-cooling class

Redundancy (from ASHRAE)

"N" represents the number of pieces to satisfy the normal conditions. Redundancy is often expressed compared to the baseline of "N." Some examples are "N+1," "N+2," "2N," and 2(N+1). A critical decision is whether "N" should represent just normal conditions or whether "N" includes full capacity during off-line routine maintenance. Facility redundancy can apply to an entire site (backup site), systems, or components. IT redundancy can apply to hardware and software

Reference Time

The amount of time that a particular benchmark took to run on a specific reference platform

Refrigerants

In a refrigerating system, the medium of heat transfer that picks up heat by evaporating at a low temperature and pressure and gives up heat on condensing at a higher temperature and pressure

Relative Humidity (RH)

* Ratio of the partial pressure or density of water vapor to the saturation pressure or density, respectively, at the same dry-bulb temperature and barometric pressure of the ambient air
* Ratio of the mole fraction of water vapor to the mole fraction of water vapor saturated at the same temperature and barometric pressure at 100% relative humidity, the dry-bulb, wet-bulb, and dew-point temperatures are equal

Releasing Panel

A particular fire alarm control panel whose specific purpose is to monitor fire detection devices in a given area protected by a suppression system and, upon receiving alarm signals from those devices, actuate the suppression system

Reliability (from ASHRAE)

A percentage value representing the probability that a piece of equipment or system will be operable throughout its mission duration. Values of 99.9% (three 9s) and higher are common in data and communications equipment areas. For individual components, the reliability is often determined through testing. For assemblies and systems, reliability is often the result of a mathematical evaluation based on the reliability of individual components and any redundancy or diversity that may be employed

Reliability (from ASHRAE, industry)

Reliability is a percentage value representing the probability that a piece of equipment or system will be operable throughout its mission duration. Values of 99.9 percent (three 9s) and higher are common in data and communications equipment areas. For individual components, the reliability is often determined through testing. For assemblies and systems, reliability is often the result of a mathematical evaluation based on the reliability of individual components and any redundancy or diversity that may be employed

Remote Power Panel (RPP)

A term typically used to describe electrical panels outside of electrical equipment rooms

Reporting Rules

The set of benchmark rules that defines what constitutes a valid full disclosure for that benchmark. Usually these define what parts of the benchmark configuration and the system configuration(s) that need to be detailed and disclosed

Response Time

The amount of time from when an action is requested until the time that the request completes and is returned to the requestor

Result

The value of the primary metric being reported for the benchmark

Return Air (RA)

See air, return

RHI

Return Heat Index

Riser

A vertical pipe in a building

Room Load Capacity

The point at which the equipment heat load in the room no longer allows the equipment to run within the specified temperature requirements of the equipment. The load capacity is influenced by many factors. The primary one is the room's theoretical capacity. Other factors, such as the layout of the room and load distribution, also influence the room load capacity

Room Theoretical Capacity

The capacity of the room based on the mechanical room equipment capacity. This is the sensible tonnage of the mechanical room for supporting the computer or telecommunications room heat loads

Rotary Heat Exchanger

See exchanger, rotary heat

Rotary UPS

See UPS, rotary

Router

A layer 3 interconnection device that appears as a media access control (MAC) to a CSMA/CD collision domain (see IEEE Std 610.7-1995 [B38])

Run Rules

The set of benchmark rules that defines what constitutes a valid test with that benchmark. Usually these define legal configurations, experimental limitations, and any operating constraints