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"High Nines"     Traditionally, you achieve reliable power with an electrical system design that uses the local utility AC
of Reliability   power grid, standby diesel generators, and an uninterruptible power supply (UPS). Operating as part of
Mean             a high reliability system, a typical UPS system offers 99.9% reliability, or three nines. Adding more
                 redundant features can boost a UPS system up to four nines of reliability.

                 While this may sound like an exceedingly high degree of reliability for many firms, three nines of
                 reliability translates into 53 minutes of downtime per year. i

3-phase          The power plant produces three different phases of AC power simultaneously, and the three phases are
power            offset 120 degrees from each other. There are four wires coming out of every power plant: the three
                 phases plus a neutral or ground common to all three. It is simply three single phases synchronized and
                 offset by 120 degrees.

Blade Server     A blade server is a thin, modular electronic circuit board, containing one, two, or more microprocessors
                 and memory, that is intended for a single, dedicated application (such as serving Web pages) and that
                 can be easily inserted into a space-saving rack with many similar servers.

brick server     A compact computer server module without a chassis that can come in various processor, RAM, I/O,
                 and storage configurations and is designed to fit into rack locations similar to those for blade servers.
                 Like blade servers, brick servers are intended to fit in multiple numbers into a rack that provides a
                 shared back plane. Blade and brick servers allow more servers to be contained in the same floor space
                 than the more conventional pizza box servers with a chassis. The term, used by Dell and others,
                 suggests that a brick server, when available, will be more brick-like in shape than a blade server. Dell
                 refers to it as a "super-blade server."ii

Computer         A room whose primary function is to house computer equipment.

CRAC             Computer Room Air Conditioner – An air conditioner specifically designed to provide cool air for
                 computer rooms.
Data Center   A building or a portion of a building whose primary function is to house a computer room and its
              related support areas.

Hot Aisle /   Refers to a layout scheme for arranging cabinets and floor tiles in a coordinated fashion when the
Cold Aisle    raised access floor is being used as a plenum area. The objective is to facilitate the front to rear
              cooling scheme of the servers. In essence, cabinets are aligned front-to-front and back-to-back. The
              floor tiles in the aisles facing the cabinet front are perforated to allow it to fill with cool air (hence cold
              aisle). The floor tiles in the aisles facing the cabinet rears are solid with the CRAC air returns located
              above the aisle in the ceiling (the hot aisle).

Hot           Sometimes referred to as “Hot Pluggable”. Describes a feature of a component of a device (e.g. power
Swappable     supply of a server, or a blade from a switch) where that component can be disconnected from the
              chassis and replaced while the chassis is „live‟.

KVM           Keyboard / Video / Mouse – typically refers a switch which allows an operator to monitor, control, and
              administer multiple servers from a single workstation by allowing him / her to toggle from server to

Media Strip   Also called a Vertical Patch Panel – a device from Hubbell Premise Wiring that allows all low voltage
              connections (primary / secondary data & KVM) to be located in the same rack position as the server
              they work for. This allows the use of the shortest jumper length possible, which in turn minimizes
              airflow congestion in the rear of the cabinet.

NOC           Network Operating Center – The area of a data center where operators can monitor the performance
              network devices and administer equipment in need of maintenance. Almost always, the NOC is located
              in a room separate from the computer room.

PDU           Power Distribution Unit – A device that takes a connection of higher power (e.g. 30A single phase
              circuit) and provide receptacles for many lower power branch circuits or power strips. They typically
              provide circuit breaker protection for each of the branch circuits.
pizza box      The term refers to the shape of a computer server enclosed in a rectangular and horizontally-arranged
server         chassis and often installed in a rack with similar servers. In any country where Italian pizza can be
               ordered for home or office delivery, it comes in a box of roughly the same size as one of these servers.

Raised floor   A false floor analogous to dropped ceiling where utilities like power and data are run from sources to
               destination cabinets.

Redundancy     The practice of building in back up sources and pathways to maintain operation in the event of failure.

SAN            Storage Area Network – a dedicated network connecting servers with specialized storage devices that
               are used to back up data and store high volume content such as video.

Server         A machine whose sole purpose is to supply data so that other machines can use that data. This also
               describes any software process that runs on a server machine and responds to client processes or
               programs locally or across a network. See also client/server. iii

Server Farm    A group of servers usually located in a secure area, and sometimes collocated at an ISP. These servers
               all serve a single purpose (such as serving Web pages, for example) and have some sort of load
               balanced across them. If one server in the farm dies, business carries on as usual. If performance is
               slow, you add more servers. This term is popular when dealing with Web-based applications, where a
               group of webservers all serve up the same content or pull data from a database server or group of
               database servers.

Site PDU       A large PDU that serves an entire or large portion of a data center. Typically, a Site PDU performs one
               or more of the following functions:

                   1. Convert for primary to secondary power source in the event of a failure.

                   2. Provide battery backup.

                   3. Provide power conditioning (filtering and surge suppression).

                   4. Provide protection (circuit breaker panel) for the area served.
UPS             Uninterruptible Power Supply - A device that contains a battery and some circuitry to supply your
                computer with power for a limited time (depending on the battery) if there is any sort of interruption in
                the outlet power. It must switch to battery power fast enough to keep the computer running during an
                outage. Large UPS‟s typically use lead-acid batteries like the one in your car. iv