Glossary
Terms, A to Z
The words you'll hear on a data-hall floor, in plain English.
A
- Availability
- The share of time a system or service is working as expected, often tracked per month or year.
C
- Colocation
- A data centre where a provider rents space, power and cooling to many customers, who bring their own IT equipment.
- Concurrently maintainable
- A design where any single component or path can be taken out for planned maintenance without shutting down IT (Tier III).
- Containment
- Physically separating hot and cold air in the data hall (hot-aisle or cold-aisle containment) so cooling works more efficiently.
- CRAH
- Computer Room Air Handler: a cooling unit that uses chilled water and fans to cool the data hall.
D
- Data hall
- The room that holds the racks of servers, storage and network equipment. Also called white space.
E
- Edge
- Small data centres located close to users to reduce latency.
- Enterprise data centre
- A data centre owned and used by a single organisation for its own IT.
F
- Fault tolerant
- A design that keeps running through any single unplanned failure, with independent, separated systems (Tier IV).
G
- Generator
- A diesel or gas engine that produces backup power when the utility supply fails.
- Grey space
- The plant areas that support the IT: electrical rooms, UPS, batteries, generators, chillers and pumps.
H
- Hyperscale
- Very large data-centre campuses built for cloud and AI companies, often tens to hundreds of megawatts each.
I
- IT load
- The electrical power available for, or used by, IT equipment, usually measured in kW or MW.
M
- Meet-me room
- The room where telecom carriers and customers connect their networks inside a data centre.
P
- PDU
- Power Distribution Unit: equipment that distributes power to racks and the devices inside them.
- PUE
- Power Usage Effectiveness: total facility energy divided by IT equipment energy. 1.0 is perfect; lower is better.
R
- Rack density
- How much power one rack uses, in kW. Traditional racks use about 5–10 kW; AI racks can exceed 100 kW.
- Redundancy
- Extra components or paths so the site keeps running when one fails, described as N, N+1 or 2N.
S
- Single point of failure
- Any component whose failure would stop the whole system.
T
- Tier
- The Uptime Institute classification (I to IV) that describes how resilient a data centre's infrastructure design is.
U
- UPS
- Uninterruptible Power Supply: batteries and electronics that keep IT powered instantly during a utility failure, until generators start.
- Uptime
- Time during which a system is running. Also the name of the Uptime Institute, which publishes the Tier standard.
- Uptime Institute
- An organisation that publishes the Tier Classification System and certifies data-centre designs, facilities and operations.
W
- White space
- The area of a data centre that houses IT equipment. See data hall.
- Wholesale
- Colocation where whole halls or buildings are leased to a single large customer.
- WUE
- Water Usage Effectiveness: litres of water used per kWh of IT energy.