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edge switch 2/16 service manual Glossary–51
Glossary
UNIX
A popular multi-user, multitasking operating system originally designed to be a small, flexible
system used exclusively by programmers. UNIX was one of the first operating systems to be
written in a high-level programming language, namely C. This meant that it could be installed
on virtually any computer for which a C compiler existed. Due to its portability, flexibility, and
power, UNIX has become the leading operating system for workstations. Historically, it has
been less popular in the personal computer market, but the emergence of a new version called
Linux is revitalizing UNIX across all platforms.
upper level protocol
ULP. Protocols that map to and run on top of the Fibre Channel FC-4 layer. ULPs include
Internet protocol (IP) and small computer system interface (SCSI).
UPS
See uninterruptable power supply.
user datagram protocol
UDP. A connectionless protocol that runs on top of Internet protocol (IP) networks. User
datagram protocol/Internet protocol (UDP/IP) offers very few error recovery services, instead
providing a direct way to send and receive datagrams over an IP network. UDP/IP is primarily
used for broadcasting messages over an entire network. Contrast with transmission control
protocol/Internet protocol.
V
VAC
See volts alternating current.
VDC
See volts direct current.
virtual machine
VM®. (1) A virtual data processing system that appears to be at the exclusive disposal of a
single user, but whose functions are accomplished by sharing the resources of a real data
processing system. (2) A functional simulation of a computer system and its associated
devices, multiples of which can be controlled concurrently by one operating system (D, T).