Data Center Terms
2N
A redundancy model that ensures that every component has a backup such that the data center has no single point of failure.
AC
Alternating Current, the designation given to power that is delivered in the form of a sinusoidal wave form. AC won out over DC as the preferred method of delivering and using power in the industrial age due to the ease of voltage transformation using static devices (transformers).
ACAE
Air Conditioning Airflow Efficiency, the amount of heat removed per standard cubic foot of airflow per minute.
Acme
This is a test of the dictionaries.
AHU
Air Handling Unit.
Air-sampling
Sampling smoke detector, sometimes called a VESDA system, is capable of detecting microscopic particles of smoke.
Airside Economizer
A device consisting of fans, ducting and a control which utilizes outside air directly to cool the data center when environmental conditions allow. Air is typically filtered, brought into existing distribution system and then exhausted back to the atmosphere.
Aisle
The open space between rows of racks. Best-practice dictates racks should be arranged with consistent orientation of front and back to create ?cold'and ?hot'aisles.
Amps
ampere (A, amp) A unit of measurement of electric current. One ampere is equal to the current produced by one volt flowing through a resistance of one ohm.
AMS
Asset Management System.
BACnet
A data communication protocol for building automation and control networks.
BAS
Building Automation System.
Blanking Panel
A device mounted in unused U spaces in a rack that restricts recirculation airflow, also called blanking or filler plates.
BMS
Building Management System, synonymous with BAS, AMS and other computer-based tools used to manage data center assets.
BTU
British Thermal Unit, a unit of energy. 1kWh = 3412btu. Cooling equipment capacity is commonly specified in btu/hr.
Burn-in
A test in which a system or component is made to run for an extended period of time to detect problems.
Bypass Airflow
Conditioned air that does not reach computer equipment. With fixed speed fans (common in DX equipment), some bypass air is inevitable and without containment, some bypass air is prudent. Unintended bypass air can occur by escaping through cable cut-outs, holes under cabinets, misplaced perforated tiles or holes in the computer room perimeter walls.
C/H
Cooling/Heating.
Cabinet
Device for holding IT equipment, also called a rack.
CAC
Cold Aisle Containment system that directs cooled air from air conditioning equipment to the inlet side of racks in a highly efficient manner.
CADE
Corporate Average Data Center Efficiency.
Calibrated Vectored Cooling (CVC)
An air-cooling technology developed by IBM for serversystems with high component density. CVC optimizes the path of air flow through the equipment, increasing the efficiency with which heat is removed.
CapEx
Capital Expense, the cost of purchasing capital equipment.
Carobn Footprint
A measurement of the volume of Carbon Dioxide generated by business operations, units are commonly metric tons.
Category 6 Cable
Commonly referred to as Cat-6, is a cable standard for Gigabit Ethernet and other network protocols that is backward compatible with the Category 5/5e and Category 3 cable standards. Cat-6 features more stringent specifications for crosstalk and system noise. The cable standard provides performance of up to 250 MHz and is suitable for 10BASE-T / 100BASE-TX and 1000BASE-T / 1000BASE-TX (Gigabit Ethernet). It is expected to suit the 10GBASE-T (10Gigabit Ethernet) standard, although with limitations on length if unshielded Cat 6 cable is used. Category 6 Cable can be identified by the printing on the side of the cable sheath.
CCTV
Circuit television (CCTV) A private television system, typically used for security purposes, in which the signal is transmitted to a limited number of receivers.
Ceiling to Deck Height
The space between a suspended or false ceiling and the structural surface above used as a distribution system that provides a pathway for cables serving the work area outlets from above.
CFD
Computational Fluid Dynamics, a numerical analysis technique commonly used in the analysis of airflow in data centers.
CFM
Cubic Feet per Minute, a unit of flow rate, commonly used to specify airflow.
Checkpoint
A snapshot of the state of a virtual machine. Like a restore point in Windows operating systems, a checkpoint allows the administrator to return the virtual machine to a previous state.
Chilled Water Pumps
A type of precision cooling system widely used in mid-sized to large IT environments. A chilled water system uses water as a cooling medium. Cold water is pumped from a chiller to computer room air handlers designed to cool the space. A chilled water air conditioner can be thought of as similar to a car radiator with a fan, with hot air being cooled by being blown through a cool radiator. In a chilled water system cooling an IT facility, the chilled water may be provided as a utility in the building, or special dedicated water chillers may be installed.
Chiller
A unit consisting of a compressor, a condensing section and an expansion section. The condensing and expansion sections nearly always have water or glycol as the heat transfer agent to the rest of the system; primary water/glycol on the condensing side and secondary water on the expansion side.
Chiller Feeds
A type of precision cooling system widely used in mid-sized to large IT environments. A chilled water system uses water as a cooling medium. Cold water is pumped from a chiller to computer room air handlers designed to cool the space. A chilled water air conditioner can be thought of as similar to a car radiator with a fan, with hot air being cooled by being blown through a cool radiator. In a chilled water system cooling an IT facility, the chilled water may be provided as a utility in the building, or special dedicated water chillers may be installed.
Close-Coupled Cooling
Cooling technology that is installed adjacent to server racks, minimizing the path that air must flow from the cooling unit through the IT equipment and back to the cooling unit.
Cloud Computing
A general term for anything that involves delivering hosted services over the Internet. These services are broadly divided into three categories: Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS).
cloud storage API
An application program interface that connects a locally-based application to a cloud-based storage system, so that a user can send data to it and access and work with data stored in it. To the application, the cloud storage system is just another target device, like tape or disk-based storage.
Coefficient of Effectiveness
Uptime Institute metric based on the Nash-Sutcliffe model efficiency coefficient.
Cold Aisle
An aisle where rack fronts face into the aisle. Chilled airflow is directed into this aisle so that it can then enter the fronts of the racks in a highly efficient manner.
Cold Spot
An area where ambient air temperature is below desired levels. Typically caused by ineffective airflow management necessitating a temperature set point lower than that which would be required with proper airflow management.
Colocation
Colocation allows multiple customers to locate network, server, and storage gear- and connect them to a variety of telecommunications and network providers with a minimum of cost and complexity.
Colocation Center
A type of data center where colocation services are provided.
Condensate Piping
Water that results as a by-product of dehumidification. Condensate is usually pumped out of the IT room or data center (via a condensate pipe) into the building drainage system. Since maintaining humidity is a desired goal of a computer room air conditioning system, dehumidification is typically not a desired function. However, dehumidification and the resultant production of condensate commonly occur as a result of suboptimal design.
Content Delivery Network (CDN)
A system of computers containing copies of data placed at various nodes of a network. When properly designed and implemented, a CDN can improve access to the data it caches by increasing access bandwidth and redundancy and reducing access latency. It is often used for web objects, downloadable objects, applications, live streaming media, and database queries.
Converged infrastructure
An approach to managing a modular data center that relies on a specific vendor and the vendor?s partners to provide pre-configured bundles of hardware and software.
Cooling Tower
A device which cools water via the direct evaporation of some of the water. Water is pumped into the top of the cooling tower and allowed to run down over the fill, typically pads or strips into a sump at the bottom of the cooling tower. Air is drawn in from the sides over the fill by fans in the top of the tower, evaporating some of the water which cools the remaining water. The temperature of the water in the sump is controlled by varying the speed of the fans. The water in the sump is then used to cool the condensing section of a chiller or to cool the secondary loop directly via a heat exchanger (see water side economizer).
CRAC
Computer room air conditioner (pronounced crack) which uses refrigerant and a compressor. Cooling of the air in the data center is accomplished by airflow over the evaporation coils where the refrigerant is being "directly expanded" (see DX).
CRAH
Computer Room Air Handler (pronounced craw) which uses chilled water passing through a heat exchanger to cool air flowing over the heat exchanger.
Critical Load
Computer equipment whose uptime is critical, typically supported by a UPS.
Critical Power Distribution
Critical Load Equipment that must have an uninterrupted power input in order to prevent damage or loss to a facility, itself, or to prevent danger of injury to operating personnel.
CSI
Cold Supply Infiltration index, quantifies the amount of hot air mixing with cold inlet air prior to entering the rack.
CUE
Carbon Usage Effectiveness, a metric defined by the Green Grid, which is a measure of data center sustainability in terms of data center specific carbon emissions. CUE is calculated by dividing the ?total CO2 emissions caused by total data center energy? by the ?energy consumption of the IT computing equipment?. An alternative way to calculate CUE is by multiplying the data center?s annual PUE by the Carbon Emissions Factor for the region as determined by the EPA. The units of CUE are kilograms of carbon dioxide per kilowatt-hour.
Cutout
An open area in a raised floor that allows airflow or cable feeds.
CW
Chilled Water.
D/H
Dehumidifying/Humidifying.
Data Center Design Capacity
Capacity Planning is an essential aspect to creating, expanding, or optimizing a Data Center.
Data protection management (DPM)
The administration of backup processes to ensure that tasks run on schedule, and that data is securely backed up and recoverable. Good data protection management means having effective processes and methodologies in place to maintain data integrity.
DC
Data center.
DC
Direct Current, a non-time varying method of delivering power. While slightly more efficient then AC if utilized between the DC portion of the UPS and the power supplies in IT equipment, it has not won wide acceptance in modern data centers.
DCiE
Data Center infrastructure Efficiency, a metric developed by the Green Grid, data center infrastructure efficiency is an efficiency measure that is calculated by dividing the IT equipment power consumption by the power consumption of the entire data center. This measure is the inverse of PUE.
Dead Band
A control technique which prevents oscillation or unnecessary cycling of a controlled variable. In data center cooling, it typically applies to the action of the CRAC or CRAH relative to the set point. A certain amount of dead band around the set point prevents unnecessary cycling of the compressor or chilled water valve.
Delta T
The difference in temperature across a device. Examples include the temperature difference between the inlet and outlet of piece of IT equipment or between the inlet and outlet of a cooling unit (CRAC or CRAH). Delta T, airflow and thermal dissipation are related: thermal dissipation = airflow x delta T x specific heat of air.
Demand signal repository (DSR)
A database that aggregates sales data at the point of sale (POS). DSR systems capture, clean and harmonize large data sets so the data can be queried. The goal of a DSR system is to allow a business user without technical knowledge to be able to identify what products are selling, where they are selling best or worst and how often they are being sold. This information can then be applied to determine how an organization can be more responsive to customer's needs.
Dewpoint
The temperature at which air reaches water vapor saturation. Dewpoint is constant for a specific amount of water in a specific amount of air while relative humidity varies with temperature. The latest ASHRAE spec for data center environmental conditions includes an upper limit for humidity based on dewpoint.
Distributed Copper Infrastructure
When networking gear is pushed out to copper connectivity to centralized switch instead of using distributed switches.
Distributed Switch Infrastructure
When networking gear is pushed into individual cabinets instead of providing copper or fiber connections back to a centralized switch.
Distribution Cell
The cellular floor sections from which cables emerge into work areas.
Distribution Frame
A structure with terminations for connecting the cabling of a facility in such a manner that interconnection or cross-connections may be readily made. (TIA)
Distribution Panel
A wiring board that provides a patch panel function, and mounts either in a rack or on a wall.
Dry Cooler
A liquid-to-air heat exchanger that is a radiator over which air is blown via fans. Typically used as the heat rejection device for water or glycol cooled condensers, may also be used as the heat rejection device for liquid cooled coils in an AHU under proper environmental conditions.
Dry-Bulb Temperature
The temperature of the air measured using a dry-bulb thermometer such that evaporative cooling has no effect. Typically taken in conjunction with a wet-bulb reading which does include the evaporative cooling effect in order to determine relative humidity.
DX
An abbreviation for direct expansion. This refers to the use of refrigerant directly expanded into evaporation coils in the supply air stream of an air conditioning unit.
Economizer
A mechanical device used to reduce energy consumption. Economizers recycle energy produced within a system or leverage environmental temperature differences to achieve efficiency improvements. Economizers are commonly used in data centers to complement or replace cooling devices like computer room air conditioners (CRACs) or chillers.
EFC
Equivalent Full Cabinets, the number of full cabinets that would exist if all the equipment in the data center were concentrated in full cabinets.
Electrical Generator
a device that converts mechanical energy to electrical energy, generally using electromagnetic induction. The reverse conversion of electrical energy into mechanical energy is done by a motor; motors and generators have many similarities. A generator forces electric charges to move through an external electrical circuit, but it does not create electricity or charge, which is already present in the wire of its windings.
Electrical Service
The wiring that connects the electric utility's cables in the street to the building. Specifically, electrical service is the wiring from the street, through the meter and up to the panelboard, but no farther. Electrical service can be provided directly from the utility company's transformer or though service laterals. Besides referring to the physical wiring, the term electrical service also refers in an abstract sense to the provision of electricity to a building.
Enterprise Server
A computer containing programs that collectively serve the needs of an enterprise rather than a single user, department, or specialized application.
Enterprise Storage
A centralized repository for business information that provides common data management and protection, as well as data sharing functions, through connections to numerous (and possibly dissimilar) computer systems.
ESD
Electrostatic Discharge, more commonly ?static discharge'.
Evaporative Cooling (EC)
A strategy for cooling air that takes advantage of the drop in temperature that occurs when water that's exposed to moving air begins to vaporize and change to gas.
Firewall
A continuous barrier used to prevent fire spreading from one fire zone or area to another. One or more security mechanisms (hardware and/or software) designed to prevent, detect, suppress, and/or contain unauthorized access to a network.
Floor Drains
A fixture that provides an opening in a floor that drains water into a plumbing system.
Generator Electrical Feeds
Wires that feed from the electrical generator into the building structure.
GPM
Gallons Per Minute, a unit of flow rate.
Green Computing
The environmentally responsible use of computers and related resources. Such practices include the implementation of energy-efficient central processing units (CPUs), servers and peripherals as well as reduced resource consumption and proper disposal of electronic waste (e-waste).
Green Data Center
A repository for the storage, management, and dissemination of data in which the mechanical, lighting, electrical and computer systems are designed for maximum energy efficiency and minimum environmental impact. The construction and operation of a green data center includes advanced technologies and strategies.
HAC
Hot Aisle Containment, system that directs heated air from the outlet side of racks to air conditioning equipment return ducts in a highly efficient manner.
Hall-POD
Module or a room, segmented area of a datacenter.
Halon
Any of several compounds consisting of one or two carbon atoms combined with bromine and one or more other halogens. Halons are gases and are used as fire-extinguishing agents. They are between three and ten times more destructive to the ozone layer than CFCs are.
Hard Drive Overwriter
In e-cycling, a hard drive overwriter is a program or utility that repeatedly overwrites the data on a computer's hard drive with gibberish. Once data is saved to a hard drive, it's surprisingly persistent. Simply deleting files makes them more difficult to access, but doesn't actually get rid of them. The data remains in the hard drive until it is overwritten. By overwriting the entire hard drive with gibberish, the user ensures that their information remains inaccessible no matter where the computer might eventually wind up.
Harmonic Distortion
Distortion in the line voltage waveform. Any cyclical waveform can be described as the sum of sine waves of various magnitudes which are integer multiples of the root frequency (60 Hz, 120 Hz, 180 Hz, etc.). Harmonics are often the result of the non-linear loading of the power distribution system due to the nature of solid state power supplies. Harmonics are detrimental to the efficiency and capacity of power delivery equipment and rotating equipment due to increased eddy current losses and non-fundamental frequency torques.
HDG
Hot Dipped Galvanized.
Heat Exhanger
A device used to transfer heat energy from one medium to another. Common uses of heat exchangers are water to air heat exchangers in air handling units, plate and frame heat exchangers in economizers, etc.
Horizontal Pathways
Horizontal Cabling connects telecommunications rooms to individual outlets on the floor.
Hot Aisle
An aisle where rack backs face into the aisle. Heated exhaust air from the equipment in the racks enters this aisle and is then directed to the CRAC return vents.
Hot Spot
An area, typically related to a rack or set of racks, where ambient air temperature is above acceptable levels. Typically caused by poor airflow management (insufficient cool air supply or an excess of recirculation).
Hp
Horsepower.
HPDC
High-Performance Data Center, a data center with above average kW loading, typically greater than 10kW/rack.
HVAC
Heating, Ventilation and Air Conditioning system, the set of components used to condition interior air including heating and cooling equipment as well as ducting and related airflow devices.
In-Row Cooling
Cooling technology installed between racks in a row that draws warm air from the hot aisle and delivers cool air to the cold aisle, minimizing the path of the air (see close coupled cooling).
Incident Management (IcM)
Incident management (IcM) is an area of IT Service Management (ITSM) that involves returning service to normal as quickly as possible after an incident, in a way that has little to no negative impact on the business. In practice, incident managment often relies upon temporary workarounds to ensure services are up and running while the incident is investigated, the root problem identified and a permanent fix put in place.
Infrastructure as a Service (IaaS)
Also known as cloud intrastructure services. Delivers computer infrasturcture, typically a platoform virtualiation environment, as a service. Rather than purchasing servers, software, data center space or network equipment, clients instead buy those resources as a fully outsourced service.
Inlet Air
The air entering the referenced equipment. For air conditioning equipment this is the heated air returning to be cooled, also called return air. For racks and servers this is the cooled air entering the equipment.
Intelligent Power Management (IPM)
A combination of hardware and software that optimizes the distribution and use of electrical power in computer systems and data centers. While the installation of IPM involves up-front cost and ongoing maintenance, the technology can save money in the long term as a result of reduced electric bills, reduceddowntime and prolonged hardware life.
Internet Service Provider (ISP)
A company that provides access to the Internet.
Intrusion Detection
A network intrusion detection system (NIDS) is an intrusion detection system that tries to detect malicious activity such as denial of service attacks, port scans or even attempts to crack into computers by monitoring network traffic.
IP
Internet Protocol, a communications technology using the internet for communications.
IP Surveillance
A digitized and networked version of closed-circuit television (CCTV). In an IP surveillance system, an IP camera records video footage and the resulting content is distributed over an IP (Internet protocol) network.
IR
Infrared spectrum used by thermal imaging technologies.
JVM
Java Virtual Machine, Java interpreter. Software that converts the Java intermediate language into executable machine language.
kBTU
Kilo British Thermal Unit, one thousand BTU (see BTU).
kCFM
Kilo-Cubic Feet per Minute, one thousand CFM (see CFM).
kV
Kilovolt, one thousand volts, (see V).
kVA
Kilovolt Amperes = voltage x current (amperage) (see VA).
KVM
Keyboard, Video, Mouse, an interface technology that enables users to access multiple servers remotely from one or more KVM sites. More obscurely, can also mean Kernel-base Virtual Machine: a version of the Java Virtual Machine for small devices with limited memory.
kW
Kilowatts, one thousand watts (see W).
kWh
Killowatt-Hour, one thousand watt hours (see Wh). kWh is a common unit of electrical energy.
Latent Cooling
The process of condensing water out of air, then evaporating the water later. Energy is given up by the water during condensation. If the water is then later evaporated (such as from a drip tray), the amount of energy used to evaporate the water is the same as the amount of energy given up by the water vapor to the cooling equipment when it was condensed. Cooling is occurring later in time, hence the name "latent cooling". In a system where condensed water is pumped or drained away, the cooling that may occur from evaporation does not cool the environment where the condensation took place so the cooling capacity spent condensing the water vapor is wasted energy.
Latent Cooling Capacity
Cooling capacity related to wet bulb temperature and objects that produce condensation.
Line Noise
Distortions superimposed on the power waveform that may cause electromagnetic interference.
Liquid Cooling
A general term used to refer to cooling technology that uses a liquid evacuate heat. In data centers, the two prevalent forms of heat evacuation are liquid (chilled water) and refrigerant (DX).
Load
The demand placed on a system, typically used to describe the electrical demand on the electrical supply system or the cooling demand on the cooling system. Units are power such as kW, BTU/hr, Tons, etc.
Load Balancing
A methodology to distriubute workload across multiple computers or a computer cluster, network links, center processing units, disk drives, or other resources, to achieve optimal resource utilization, mixmize throughput, minimize response time, and avoide overload.
Logical Network
A network that appears to the user as a single, separate entity although it might in fact be either an entity created from mutliple networks or just a part of a larger network. A logical network is defined by its IP addressing scheme.
Low Voltage System
Low voltage is an electrical engineering term that broadly identifies safety considerations of an electricity supply system based on the voltage used. While different definitions exist for the exact voltage range covered by "low voltage", the most commonly used ones include "mains voltage". "Low voltage" is characterized by carrying a substantial risk of electric shock, but only a minor risk of electric arcs through air.
MAH
Makeup Air Handler, an air handler that conditions and delivers outside air into an occupied space.
Make-Up Air
The conditioned air delivered by a MAU or MAH.
Managed File Transfer (MFT)
A type of software used to provide secure internal, external and ad-hoc data transfers through a network. MFT products are built using the FTP network protocol. However, because federal regulations require that MFT products meet strict regulatory compliance standards, they include mechanisms to ensure a higher level of security and help keep information private.
MAU
Makeup Air Unit, synonymous with MAH.
Maximum Temperature Rate of Change
An ASHRAE standard established to ensure stable air temperatures. The standard is 9 degrees F per hour.
Memory Overcommit (Overcommitment)
A hypervisor feature that allows a virtual machine (VM) to use more memory space than the physical host has available.
MERV
Minimum Efficiency Reporting Value, ASHRAE 52.2, for air filtration measured in particulate size.
Modular, non-scalable UPS
based on incriminated growth based on size rating, can modularly increase power capacity.
N+1
Need plus one, a redundancy concept where capacity is configured to include used capacity plus one additional device to enable continued operations with the failure of one system in the configuration.
NEBS
Network Equipment-Building System design guidelines applied to telecommunications equipment.
Network Cabinets
A cabinet designed to hold a series of controllers, all connected via a telecommunications cable.
Network Engineer
One who handles all of the "plumbing" for a company's computers, connecting offices with T1 lines, hooking them up to the Internet, and configuring all internal systems such as net routers and firewalls.
Network Operations Center (NOC)
A network operations center (or NOC, pronounced "nock") is one or more locations from which control is exercised over a computer, television broadcast, or telecommunications network. Large organizations may operate more than one NOC, either to manage different networks or to provide geographic redundancy in the event of one site being unavailable or offline. NOCs are responsible for monitoring the network for alarms or certain conditions that may require special attention to avoid impact on the networks performance. For example, in a telecommunications environment, NOCs are responsible for monitoring for power failures, communication line alarms (such as bit errors, framing errors, line coding errors, and circuits down) and other performance issues that may affect the network. NOCs analyze problems, perform troubleshooting, communicate with site technicians and other NOCs, and track problems through resolution. If necessary, NOCs escalate problems to the appropriate personnel. For severe conditions that are impossible to anticipate ? such as a power failure or optical fiber cable cut ? NOCs have procedures in place to immediately contact technicians to remedy the problem.
Nominal Cooling Capacity
The total cooling capacity of air conditioning equipment, includes both latent cooling and sensible cooling capacities.
OpEx
Operating Expense, the ongoing expenses related to operating the data center.
Overcooling
A situation where air is cooled below optimum levels. Typically used in reference to rack inlet temperatures.
Packet Acceleration
TCP acceleration is the name of a series of techniques for achieving better throughput on an Internet connection than standard TCP achieves, without modifying the end applications. It is an alternative or a supplement to TCP tuning.
PDU
Power Distribution Unit, this typically refers to one of two pieces of equipment in the power delivery chain. One is the combination transformer/breaker panel that is often used between a UPS supplying voltage higher than that used by the IT equipment and the cabinets. The other is the smaller "power strip" like device that is used inside the rack to distribute power to the IT equipment.
Peltier Effect
A temperature difference created by applying a voltage between two electrodes connected to a sample of semiconductor material. This phenomenon can be useful when it is necessary to transfer heat from one medium to another on a small scale. The Peltier effect is one of three types of thermoelectric effect; the other two are theSeebeck effect and the Thomson effect.
Perimeter Cooling
A solution that enables monitoring and maintenance of temperature and humidity design conditions which is critical to the smooth operation of a data center or computer room. Tight tolerance temperature control is essential as temperature fluctuations can cause thermal stresses and premature failures in IT equipment. Low humidity can cause static discharge and high humidity can cause condensation ? both extremes creating treacherous conditions for IT and networking equipment. Additionally, Perimeter Cooling solutions are highly manageable with controls to ensure optimized operation, alarms to provide visibility into the health of the unit, and an easy-to-use display allowing the operator to select options from the device's menu-driven interface to control and monitor the connected air conditioning system.
PF
Power Factor represents the portion of the apparent power that is real power. The source of power factor is non-resistive components (inductors and capacitors) in the load on an AC power system. These components draw current that is 90 degrees out of phase with the voltage across them resulting in zero real power being delivered. While the power delivery system must carry this current (as well as all the current which does result in real power being delivered), it does no useful work. Power companies often charge a penalty for loads which have a power factor that is significantly far away from 1.0 since the size of the equipment that must be in place is dependent upon the total current delivered, but normal billing is based on real power delivered.
PH
Phase, a term that describes the relationship between multiple time-varying waveforms which have a constant frequency but differ in their position relative to time. It is also used to refer to the number of sinusoidal voltages that make up the power delivery to a device. Most common are three-phase and single-phase. Single-phase consists of 2 conductors between which a sinusoidal voltage is present. Three-phase is a set of 3 or 4 conductors. In the case of 3 conductors, a sinusoidal voltage of a constant magnitude and frequency but differing relationship with respect to time exists between any 2 conductors. In a 4 wire system, the same voltage as in the 3 wire case exists between any of the three "hot" conductors and in addition, between any of the three "hot" conductors and fourth neutral conductor there exists a voltage that is smaller by a factor of the square root of three than the voltage between any of the "hot" conductors. An example of this is a 208/120 three-phase system. 208 volts exists between any of the three "hot? conductors and 120 volts exists between any of the "hot" conductors and the neutral conductor.
Phase-change Cooling (Vapor Cooling)
A microprocessor-cooling technology that works according to the same principles as a conventional refrigerator, freezer or air conditioner.
Plate and Frame
A type of heat exchanger commonly used in water-to-water systems. It is a series of plates held in a frame through which exists 2 paths for water which are adjacent but separate. Plate and frame heat exchanges are simple to size via the addition of additional components and maintenance is straight-forward via disassembly.
Platform as a Service (PaaS)
A way to rent hardware, operating systems, storage and network capacity over the Internet. The service delivery model allows the customer to rent virtualized servers and associated services for running existing applications or developing and testing new ones.
Plenum
A receiving chamber for air used to direct air flow.
Pole
A row of power receptacles with power supplied from a PDU.
Pole Position
A power receptacle on a pole.
Power
Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt. Electrical power is distributed via cables and electricity pylons like these in Brisbane, Australia. When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work. Devices convert electrical energy into many useful forms, such as heat (electric heaters), light (light bulbs), motion (electric motors), sound (loudspeaker) or chemical changes. Electricity can be produced mechanically by generation, or chemically, or by direct conversion from light in photovoltaic cells, also it can be stored chemically in batteries.
Power Density
Electrical power used in a space divided by the area of the space.
Power Factor
Amount of power loss due to the amount of power conversion.
PreAction
An Action involved in a dry system prior to actually flooding the pipe with water and potentially discharging into the protected space.
Pressure Differential
The difference in pressure between two locations in the data center. Air flows from higher pressure areas to lower pressure areas. Often times, the pressure differential between the under-floor plenum and the above-floor space is controlled by varying the speed of the fans supplying air to the under-floor plenum. This allows the addition of vented floor tiles to occur without affecting the air delivered to existing vented floor tiles so that additional IT load may be placed on the floor without disturbing the tuning of the existing floor.
Primary Core Switch and Redundant Core Switch
Each PCR room has two core switches, one is primary and the other is redundancy. Between PCR room's core switches, every building's core switch has two links to other building's core switches. One link to core switches of primary and the other link to core switches of redundancy.
Primary Loop
Refers to the water loop which cools the condenser side of a chiller. This loop is cooled by dry coolers or cooling towers.
Private Cloud (Internal cloud or corporate cloud)
A proprietary computing architecture that provides hosted services to a limited number of people behind a firewall.
PU
Packaged Unit, an air handler that is a complete device shipped ready for use rather than a custom device that is assembled on-site from components.
PUE
Power Usage Effectiveness, a metric defined by the Green Grid, which is a measure of data center efficiency calculated by dividing the total data center energy consumption by the energy consumption of the IT computing equipment. This measure is the inverse of DCiE.
Pumps
A pump and enclosure used to circulate condenser water or glycol on applicable systems. Pump packages are specified based on desired flow rate and piping losses for each application.
Rack
Device for holding IT equipment, also called a cabinet.
Rack Unit (RU)
a unit of measure of vertical space in an equipment rack. One rack unit is equal to 45 mm (1.75 in).
RAH
Recirculation Air Handler, a device that circulates air but does not cool the air.
Raised Floor
Metal flooring on stanchions that creates a plenum for airflow and cabling, synonymous with RMF.
Recirculation
Air which exits IT equipment and then re-enters either the same IT equipment or another piece of IT equipment without being cooled. Typically caused by poor control of airflow due to missing blanking panels, gaps in rows, insufficient air supply, etc.
Redundancy
The duplication of critical components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe.
Remote Data Backup
The process of backing up data created by remote and branch offices (ROBOs) and storing it securely. Businesses with ROBOs require backup and recovery solutions that can support the company's data protection policies and business service levels.
Remote Replication
The process of copying production data to a device at a remote location for data protection or disaster recovery purposes.
Return Air
The heated air returning to air conditioning equipment.
RFI
Radio Frequency Interference.
Rh
Relative Humidity.
RMF
Raised Metal Floor, an alternate term for the more commonly used term ?raised floor'.
ROI
Return on Investment, a measure of the money that an entity earns as a percentage of the total value of its assets that are invested.
Router
Router An internetworking device, operating at the Network layer of the Open Systems Interconnection model, used to direct packets from one network to another.
Row-based cooling
Row-Based Cooling solutions provide cooling directly to multiple adjacent cabinets. These solutions are typically deployed in locations that do not have traditional computer room air conditioning. They may also be implemented to augment existing cooling, especially in areas where cabinets are densely populated. Options range from medium-density (5 to 7kW per cabinet) to high-density (20+ kW per cabinet).
RPM
Revolutions per Minute, a unit of angular velocity.
RPP
Remote Power Panel.
RTU
Rooftop Unit, an air handler designed for outdoor use mounted on a rooftop.
S+S
System plus system.
Satellite Head End System
An equipment rack filled with active electronics capable of receiving, processing and delivering digital satellite TV signals to an entire community over coaxial cable and/ or fiber optic infrastructure. Head end systems are used by both franchised and non-franchised cable companies to provide video, Internet and telephone services to customers.
SCFM
Standard Cubic Feet per Minute, the volumetric flow rate of a gas corrected to standardized conditions of temperature, pressure and relative humidity.
Secondary Loop
Refers to the water which is used to cool the heat exchangers in AHUs and is cooled via the expansion unit in a chiller.
Seebeck Effect
A phenomenon in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances.
Sensible Cooling
The action of lowering the dry bulb temperature of air without condensation taking place.
Server Cabinets
A cabinet designed to hold a network device that combines hardware and software to provide and manage shared services and resources on the network.
Server Core
A bare-bones installation option for computers running the Windows Server 2008 operating system. The installation results in a server environment that is easy to manage and maintain but offers less functionality than more complex options.
Set Point
In a control system, this is the value against which the variable that is being controlled is compared. Temperature and humidity set points are common in the cooling system for a data center.
Short Cycling
Chilled airflow returning to cooling units without passing through IT equipment, also referred to as bypass.
Softcooling (Software Cooling)
A software-based method of computer component cooling, conducted either by adjusting component settings or by using softcooling products. The practice reduces system heat by decreasing the power used by the CPU, graphics card andmotherboard when the computer is idle or under light use.
Standard Temperature and Pressure (STP)
Standard temperature and pressure, abbreviated STP, refers to nominal conditions in the atmosphere at sea level.
Step Down Transformers
A transformer that reduces voltage - an electrical device by which alternating current of one voltage is changed to another voltage
STS
Static Transfer Switch, a solid state device which transfers the feed of power from one source to another source such as from the incoming utility to a generator.
Sub-Floor
The open area underneath a raised computer floor, also called a sub-floor plenum.
Supply Air
The cooled airflow emitted from air conditioning equipment.
Switch 1
A network access device that provides a centralized point for LAN communications, media connections, and management activities where each switch port represents a separate communications channel. Sometimes referred to as a multi-port bridge. See also bridge. 2. A voice communications device that utilizes switching technology to establish and terminate calls.
Switchgear
Electrical Distribution hat breaks out power from high to medium to low voltage.
Switching 1
Networking protocol in which a station sends a message to a hub, which then routes the message to the specified destination station. 2. Establishing a direct signal path form one device to another. Establishing a direct signal path from one device to another.
TCE
Triton Coefficient of Effectiveness, a data center efficiency metric developed by the Uptime Institute synonymous with UCE. (see also CoE)
Telco
In the United States and possibly other countries, "telco" is a short form for Telephone Company. Sometimes it means a local telephone company, such as a Bell operating company or an independent local telephone company. Sometimes it means any telephone company, including one offering long-distance services.
Telephony
The general use of equipment to provide voice communication over distances, specifically by connecting telephones to each other.
Thermistor
A type of resistor with resistance varying according to its temperature.
Thermoelectric Cooling
Thermoelectric cooling is a way to remove thermal energy from a medium, device or component by applying a voltage of constant polarity to a junction between dissimilar electrical conductors or semiconductors.
Thin Client (Lean Client)
A low-cost, centrally-managed computer devoid of CD-ROM players, diskette drives, and expansion slots. The term derives from the fact that small computers in networks tend to be clients and not servers. Since the idea is to limit the capabilities of these computers to only essential applications, they tend to be purchased and remain "thin" in terms of the client applications they include. As software as a service (SaaS) gains popularity, it is expected that thin clients and blade PCs will replace desktop PCs in many work and educational environments.
Tier I
Composed of a single path for power and cooling distribution, without redundant components, providing 99.671% availability.
Tier II
Composed of a single path for power and cooling distribution, with redundant components, providing 99.741% availability
Tier III
Composed of multiple active power and cooling distribution paths, but only one path active, has redundant components, and is concurrently maintainable, providing 99.982% availability
Tier IV
Composed of multiple active power and cooling distribution paths, has redundant components, and is fault tolerant, providing 99.995% availability.
Tons
Ton (Cooling) A measurement of heat energy commonly used historically to measure heat loads in data centers and IT rooms in North America. A ton is equal to 12,000 BTUs and is the amount of heat energy required to melt 2000 pounds (907kg) of ice in one hour. This is an archaic term typically used to specify heat output when expressed in Tons/day, where the use of the more modern term Watts is the simpler and more universal measure that should be used.
Traditional, non-scalable UPS
Based on a particular size rating. It is fixed and cannot be increased or decreased.
Transformer
Designed to increase or decrease available voltage by electromagnetic conversion. (Exception: can also convert AC- DC)
Transition Operating System
An operating system (commonly abbreviated to either OS or O/S) is an interface between hardware and user; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer. The operating system acts as a host for applications that are run on the machine. As a host, one of the purposes of an operating system is to handle the details of the operation of the hardware. This relieves application programs from having to manage these details and makes it easier to write applications. Almost all computers, including handheld computers, desktop computers, supercomputers, and even video game consoles, use an operating system of some type. Some of the oldest models may however use an embedded operating system, that may be contained on a compact disk or other data storage device.
TVSS
Transient volt surge suppression; shunt to ground over volt spikes to prevent electrical fires and/or system failures.
U
A unit of space in a rack, equal to 1.75". The vertical dimension of racks and IT equipment is often specified in "Us" such as 42U.
UCE
Upsite Coefficient of Effectiveness, a data center efficiency metric developed by the Uptime Institute synonymous with UCE. (see also CoE)
Unified Computing System (UCS)
A unified computing system (UCS) is a data center architecture that integrates computing, networking and storage resources to increase efficiency and enable centralized management. When UCS is sold as a product, hardware and software are designed or configured to work together effectively.
Uninterruptible Power Supply (UPS)
A device that allows your computer to keep running for at least a short time when the primary power source is lost. It also provides protection from power surges. A UPS contains a battery that "kicks in" when the device senses a loss of power from the primary source. If you are using the computer when the UPS notifies you of the power loss, you have time to save any data you are working on and exit gracefully before the secondary power source (the battery) runs out. When all power runs out, any data in your computer's random access memory (RAM) is erased. When power surges occur, a UPS intercepts the surge so that it doesn't damage your computer.
UPS
Uninterruptible Power Supply, a device placed in series with the supply of power from the utility which contains energy storage such that the supply of power from the UPS is continuous even when the utility supply is removed. While battery-based energy storage is the most common, flywheel-based energy storage is gaining in popularity due to the reduced maintenance cost.
Usable KVA per Circuit
De-rating of available Kilo-volt-amps to usable amps to prevent circuit overloads and fires.
Usable kW pwer Circuit
De-rating of available Kilo-watts to usable amps to prevent circuit overloads and fires.
Usable VA per Circuit
De-rating of available volt-amps to usable amps to prevent circuit overloads and fires.
Utility Storage
A service model in which a provider makes storage capacity available to an individual, an organization or a business unit on a pay-per-use basis. The utility model is sometimes called metered services or storage on demand.
V
Volt, a unit of electrical potential.
VA
Volt-Amp, a unit of apparent power. In AC circuits, the magnitude of the voltage across a circuit times the current through the circuit is the apparent power. Including a representation of the angle between the two waveforms in the form of power factor (see PF) yields the real power.
VFD
Variable Frequency Drive, a device which supplies AC power of varying frequency, typically used to control the speed of induction motors. In the data center, it is common to vary the speed of fans, pumps, and chillers.
Virtual Desktop
An individual user's interface in a virtualized environment.The virtualized desktop is stored on a remote server rather than locally. Desktop virtualization software separates the physical machine from the software and presents an isolated operating system for users.
Virtual SAN Sappliance (VSA)
A software bundle that allows a storage manager to turn the unused storage capacity in his network's virtual servers into a storage area network (SAN). The SAN provides a pool of shared storage that can be accessed by the virtual servers as needed.
Virtualization Sprawl
Virtualization sprawl occurs when the number of virtual machines on a network reaches a point where the administrator can no longer manage them effectively.
Vmware Backup
VMware backup is the copying of data on a virtual machine (VM) in a VMware environment to prevent data loss. VMware backup, and virtual server backup in general, is a common challenge for storage and backup administrators.
W
Watt, a unit of power, commonly used in electrical discussion, watts are the product of potential (volts, see V) and current (amps, see A). If the current and voltage are AC, the relationship between watts, volts and amps includes power factor (see PF), watts = volts x amps x PF.
WAN Accelerator
An appliance that optimizes bandwidth to improve the end user's experience on a wide area network (WAN).
WAN connection
A wide area network (WAN) is a computer network that covers a broad area (i.e. any network whose communications links cross metropolitan, regional, or national boundaries). Less formally, a WAN is a network that uses routers and public communications links. Contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs), which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively. The largest and most well-known example of a WAN is the Internet. A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. wide area network (WAN) A data communications system that uses telecommunications circuits to link LANs that are distributed over large geographic distances.
Water Cooling
Water cooling is a method used to lower the temperatures of computer processors, and sometimes other components such as graphics cards, using water rather than air as the cooling medium.
Waterside Economizer
A system which uses a source other than a chiller to cool the secondary loop water used by the AHUs. This typically consists of either a dry cooler or cooling tower, piping, valves and in the case of a cooling tower, it also includes a heat exchanger since the secondary loop water is treated completely differently than the primary loop water and is typically much "better" water.
Wet-Bulb Temperature
The temperature of the air measured using a wet-bulb thermometer, that is, the temperature to which a wet surface can be cooled by evaporation. This temperature is affected by both the dry bulb temperature and the dew point of the air. Dryer air has a lower wet bulb temperature. This is a design constraint when utilizing cooling towers or evaporative pads in the cooling process.
Wg
Inches of water column, a unit of pressure based on the height of a column of water supported by the pressure differential between the top and bottom of the column. 1 inch wg = .036 psi.
Work Cell
The area of a rack and the related area immediately in front of and behind the rack. Standard racks are 2 feet wide and 4 feet deep. Standard aisles are 4 feet wide, so half of that space is workspace for a given rack. This results in a standard work cell of 16 square feet. Actual work cell size varies with data center design.
WPSF
Watts per Square Foot, a unit of power density. In a data center this is a bulk term that refers to the total load in a particular space divided by the total area of that space. This is a design parameter for total capacity of the cooling and power systems and is used in conjunction with point load (the amount of load in a small space such as a rack).
Zero Client
A server-based computing model in which the end user's computing device has no local storage. A zero client can be contrasted with a thin client, which retains the operating system and each device's specific configuration settings in flash memory.