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Glossary 299

UESC (Utility Energy Service Contract)
An incentive envisioned by the U.S. federal government for efficiency
upgrades for data centers.
UNIX
The operating system originally designed by AT&T and enhanced by the
University of California at Berkeley and others. Because it was powerful and
essentially available for free, it became popular at universities. Many ven-
dors made their own versions of UNIX available—for example, IBM’s AIX,
based on OSF/1. The UNIX trademark and definition have since come
under the control of X/Open, which will issue a unifying specification.

UPS (Uninterruptible Power Supply)
UPS, also known as a battery backup, provides emergency power. A UPS
typically protects computers, telecommunication equipment, or other
electrical equipment where an unexpected power disruption could cause
injuries, fatalities, serious business disruption, or data loss. A UPS can
provide uninterrupted power to equipment, typically for 5–15 minutes,
until a generator can be turned on or utility power is restored.
ptg
URL (Universal Resource Locator)
World Wide Web name for a document, file, or other resource. It
describes the protocol required to access the resource, the host where it
can be found, and a path to the resource on that host.
VMware
A developer of virtualization software. The company is based in Palo
Alto, California. VMware's enterprise software, VMware ESX Server,
runs directly on server hardware without requiring an additional under-
lying operating system.

WAN (Wide Area Network)
A long-distance network for the efficient transfer of voice, data, and
video between local, metropolitan, campus, and site networks. WANs
typically use lower transfer rates (64Kbps) or higher-speed services such
as T3, which operates at 45Mbps. WANs also typically use common-
carrier services (communications services available to the general public)
or private networking through satellite and microwave facilities.

watt
A basic unit of electric power. Electric energy used is measured in kilo-
watt hours (KHW) that equate to using 1,000 watts of power for one
hour.