Network & Connectivity
1.6T Ethernet
1.6T Ethernet is a 1.6 terabit-per-second Ethernet interface being defined in the IEEE P802.3dj project alongside 800G, built on higher-rate 200G-per-lane signalling. Targeted at next-generation AI…
IT & Compute Infrastructure
100 kW Rack
A 100 kW Rack is a cabinet provisioned to supply and cool roughly 100 kilowatts of IT load, a density driven by dense GPU and AI…
IT & Compute Infrastructure
19-Inch Rack
A 19-Inch Rack is the standard equipment rack whose mounting rails are spaced so that installed gear presents a 19-inch (482.6 mm) front panel width, with…
Sustainability & Metrics
24/7 Carbon-Free Energy
24/7 Carbon-Free Energy (24/7 CFE) is a procurement goal in which every hour of a data center's electricity consumption is matched with carbon-free generation on the…
Resilience & Availability
2N
2N is a fully redundant configuration that duplicates the entire system, providing two complete, independent capacity sets where either alone can carry the full load. This…
Resilience & Availability
2N+1
2N+1 is a redundancy configuration that provides two full, independent systems (2N) plus one additional spare unit, so redundancy is preserved even during maintenance of one…
IT & Compute Infrastructure
30 kW Rack
A 30 kW Rack is a cabinet provisioned to supply and cool about 30 kilowatts of IT load, a density associated with high-performance and early AI…
Resilience & Availability
3N/2
3N/2 (also called distributed redundancy) is a topology that uses three capacity units to support two units' worth of load, spreading the load and reserve across…
Network & Connectivity
400G ZR
400G ZR is a coherent pluggable optics specification, defined by the Optical Internetworking Forum, that carries a 400 Gigabit Ethernet signal directly over DWDM fiber for…
Power Infrastructure
48V DC Distribution
48-volt DC distribution delivers direct current at 48 volts from a central rectifier or power shelf to servers, eliminating repeated AC-DC conversions and reducing current and…
Design & Engineering
4D BIM
4D BIM links the 3D model to the construction programme, adding time as a fourth dimension so the build sequence can be simulated and visualised against…
Design & Engineering
5D BIM
5D BIM adds cost information to the time-linked model, associating quantities and prices with model elements so budgets and cash flow update as the design and…
Network & Connectivity
800G Ethernet
800G Ethernet is an 800 gigabit-per-second Ethernet interface standardised in IEEE 802.3df, typically implemented as eight 100G electrical lanes in QSFP-DD or OSFP modules. It is…
Network & Connectivity
95th Percentile Billing
95th Percentile Billing is a method of charging for bandwidth in which usage is sampled at regular intervals over the month, the top five percent of…
Power Infrastructure
A-Side and B-Side Power
A-Side and B-Side Power refers to two independent, redundant power distribution paths (A and B) feeding the same equipment from separate sources, so that failure or…
Network & Connectivity
A-Side Demarc
An A-Side Demarc is the first of two independent demarcation points provided for a diversely routed, redundant service, terminating one of the two physical paths into…
Resilience & Availability
A/B Power Path
An A/B Power Path is a design that supplies IT equipment from two independent electrical distribution paths, the A side and the B side, each with…
Fire & Life Safety
Abort Switch
An Abort Switch is a manually operated control that, when held or activated during the pre-discharge countdown, delays or halts the release of a fire-suppression agent.…
Cooling & Environmental Control
Absolute Humidity
Absolute Humidity is the actual mass of water vapor present in a given volume or mass of air, expressed for example in grams per kilogram of…
IT & Compute Infrastructure
Accelerator
An Accelerator is specialized hardware that performs certain computations far faster or more efficiently than a general-purpose CPU, such as a GPU, TPU, FPGA or custom…
Security & Compliance
Access Control List
An Access Control List (ACL) is a defined set of rules specifying which individuals or systems are permitted or denied access to a particular resource, area,…
MEP - Electrical Systems
Access Control System
An Access Control System is an electronic security system that manages and records who may enter defined areas, using credentials such as cards, PIN codes or…
Architecture & Building Envelope
Access Hatch
An Access Hatch is a hinged or removable panel set into a floor, ceiling, roof or wall that provides entry to a concealed space such as…
Colocation & Cloud Services
Access Request
An Access Request is the formal procedure by which a colocation customer authorizes named individuals to enter the facility or their secured space, specifying identity, escort…
Colocation & Cloud Services
Access SLA
An Access SLA is a service level commitment covering how quickly and reliably a customer can gain physical entry to their equipment or space, including 24/7…
Architecture & Building Envelope
Access-Controlled Opening
An Access-Controlled Opening is a door or portal whose use is governed by an electronic access-control system, combining a reader, electric lock, position switch, request-to-exit device…
Architecture & Building Envelope
Acoustic Door
An Acoustic Door is a door assembly designed to attenuate sound transmission, achieving a rated sound reduction index (Rw) through a heavy leaf, perimeter seals and…
Architecture & Building Envelope
Acoustic Louver
An Acoustic Louver is a louver with sound-absorbing blades that permits airflow while reducing the noise passing through a ventilation opening. In data centers acoustic louvers…
Architecture & Building Envelope
Acoustic Partition
An Acoustic Partition is an internal wall designed to attenuate sound transmission between spaces, achieving a specified sound reduction rating through mass, isolation and sealing. In…
Power Infrastructure
Active Harmonic Filter
An active harmonic filter is a power-electronic device that measures load current harmonics and injects an equal, opposite current to cancel them, keeping the supply current…
Network & Connectivity
Active Optical Cable
An Active Optical Cable (AOC) is a fixed assembly with optical transceivers permanently attached to both ends of a fiber, presenting the same electrical interface as…
Cooling & Environmental Control
Active Rear-Door Heat Exchanger
An Active Rear-Door Heat Exchanger is a chilled-water coil mounted on the back of a rack with integral fans that draw server exhaust through the coil,…
Resilience & Availability
Active-Active Site
An Active-Active Site configuration runs two or more sites simultaneously, each handling live production traffic and sharing the workload while backing one another up. Because both…
Resilience & Availability
Active-Passive Site
An Active-Passive Site configuration runs production at a primary site while a secondary standby site remains idle or lightly loaded, ready to take over on failover.…
Planning, Scheduling & Project Controls
Activity
An Activity is the fundamental unit of work in a schedule, a discrete task with a defined duration, logic links to other activities, and often assigned…
Planning, Scheduling & Project Controls
Activity Code
An Activity Code is a user-defined attribute assigned to activities in Primavera P6 to classify, filter, group and report them by dimensions such as area, phase,…
Planning, Scheduling & Project Controls
Activity ID
An Activity ID is the unique alphanumeric identifier assigned to each activity in a schedule, used to reference, sort and track it consistently across updates, reports…
Planning, Scheduling & Project Controls
Actual Cost
Actual Cost (AC) is the total cost genuinely incurred for the work completed to date, drawn from cost accounts and invoices. Also called Actual Cost of…
Planning, Scheduling & Project Controls
Acumen Fuse
Acumen Fuse is a schedule and project analytics tool by Deltek that diagnoses schedule quality, logic issues and risk drivers, running metrics such as the DCMA…
Sustainability & Metrics
Additionality
Additionality is the principle that an emissions reduction or clean-energy purchase only counts if it would not have happened without the buyer's intervention. It is central…
Fire & Life Safety
Addressable Detector
An Addressable Detector is a fire detector with a unique electronic address on a signalling loop, allowing the control panel to identify the exact device and…
Cooling & Environmental Control
Adiabatic Cooler
An Adiabatic Cooler is a dry cooler enhanced with evaporative pre-cooling that wets or humidifies the incoming air to lower its temperature toward the wet-bulb during…
Architecture & Building Envelope
Adjacency Matrix
An Adjacency Matrix is a planning tool, in grid form, that records how strongly each space should be located near or apart from every other space.…
Fire & Life Safety
Agent Concentration
Agent Concentration is the proportion of suppression agent, by volume, achieved in a protected space, which must reach the design level needed to extinguish fire while…
Data Center Facility & Site
AI Factory
An AI Factory is a data center or facility purpose-built to train and run artificial-intelligence workloads at scale, densely packed with GPU or accelerator clusters. Characterized…
IT & Compute Infrastructure
AI Rack
An AI Rack is a cabinet configured for artificial-intelligence workloads, densely populated with GPU or accelerator servers, high-speed networking and often integrated liquid cooling and high-capacity…
IT & Compute Infrastructure
AI Training Cluster
An AI Training Cluster is a large group of interconnected accelerator servers dedicated to training machine-learning models on massive datasets. In data centers it demands extreme…
Operations & DCIM
AIOps
AIOps (Artificial Intelligence for IT Operations) is the application of machine learning and analytics to the streams of telemetry, logs and events a data center generates,…
Architecture & Building Envelope
Air Barrier
An Air Barrier is a continuous system of materials and seals that stops uncontrolled air leakage through the building envelope while still allowing designed ventilation. It…
Power Infrastructure
Air Circuit Breaker
An Air Circuit Breaker (ACB) is a low-voltage breaker that interrupts high currents in air, using arc chutes to stretch and cool the arc, and is…
Security & Compliance
Air Gap
An air gap is a security measure that physically or logically isolates a system or network so it has no active connection to untrusted networks such…
MEP - Mechanical Systems
Air Handling Unit
An Air Handling Unit (AHU) is a packaged assembly of fans, filters, heating or cooling coils, dampers and controls that conditions and moves air through ductwork…
MEP - Mechanical Systems
Air Separator
An Air Separator is a device that removes entrained and dissolved air from circulating water, releasing it through an automatic vent. Eliminating air prevents corrosion, noise,…
Cooling & Environmental Control
Air-Cooled Chiller
An Air-Cooled Chiller is a chiller that rejects heat directly to the atmosphere through integral condenser coils and fans, requiring no cooling tower or condenser-water system.…
Cooling & Environmental Control
Air-Side Economizer
An Air-Side Economizer uses filtered outside air to cool a data center directly when ambient conditions are favorable, reducing or eliminating mechanical refrigeration. Direct systems introduce…
Cooling & Environmental Control
Airflow Management
Airflow Management is the discipline of controlling how cooling air moves through a data center so that cold supply air reaches equipment intakes and hot exhaust…
Cooling & Environmental Control
Airflow Sensor
An Airflow Sensor is a device that measures the velocity or volumetric rate of air movement, often using thermal, vane or pressure-based principles. In data centers…
Architecture & Building Envelope
Airlock
An Airlock is a small chamber bounded by two interlocked doors that are not opened at the same time, maintaining a pressure or contamination barrier between…
MEP - Plumbing & Fire Protection
Alarm Check Valve
An Alarm Check Valve is a one-way valve installed on a wet-pipe sprinkler riser that permits water to flow toward the sprinklers while preventing backflow, and…
Operations & DCIM
Alarm Flood
An Alarm Flood is a burst of alarms arriving faster than operators can read and act on them, typically triggered by a single upstream fault cascading…
Full index — all 1,650 terms
Every term in the DC Encyclopedia, A to Z. Each entry is sourced and dated.