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Unix A 32-bit, multitasking operating system developed in the 1960s for use on mainframes and minicomputers.

unshielded When cabling has little protection of wrapping to protect it from stray electrical or radio signals. Unshielded cabling is less expensive than shielded.

unshielded twisted-pair cable (UTP) Twisted-pair cable consisting of a number of twisted pairs of copper wire with a simple plastic casing. Because no shielding is used in this cable, it is very susceptible to EMI, RFI, and other types of interference. See also crossover cable, electromagnetic interference, radio frequency interference.

upgrade To increase an aspect of a PC, for example, by upgrading the RAM (increasing the RAM), upgrading the CPU (changing the current CPU for a faster CPU), etc.

UPS See uninterruptible power supply.

uptime The amount of time a particular computer or network component has been functional.

URL See Uniform Resource Locator.

user The person who is using a computer or network.

User Datagram Protocol (UDP) Protocol at the Host-to-Host layer of the DoD model, which corresponds to the Transport layer of the OSI model. Packets are divided into segments, given numbers, sent randomly, and put back together at the receiving end. This is a connectionless protocol. See also connectionless transport protocol, Open Systems Interconnect.

user-level security A type of network in which user accounts can read, write, change, and take ownership of files. Rights are assigned to user accounts, and each user knows only his or her own username and password, which makes this the preferred method for securing files.

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