U Interface — A 2-wire ISDN circuit, essentially today's standard 1-pair telephone company local loop made of twisted-wire. The U interface is the most common ISDN interface and extends from the central office

UAM — See user authentication module.

UDF — Universal Disk Format. A file system developed by the Optical Storage Technology Association for storage of data on optical media

UDP — User Datagram Protocol. Protocol in a Host-to-Host layer which provides a low overhead, connectionless datagram delivery service. It is a fast, but unreliable, service for delivering datagram because there is no end-to-end error detection or correction and no acknowledgments of the receipt of data.

UIMPORT — A NetWare 4 command-line utility to import user information from other database formats into an NDS database.

UltraPack — A file and folder compression format that offers better compression than standard or HiPack compression

Unavailable — An unavailable button or command is displayed in light gray instead of black, and it cannot be clicked.

Unbinding — The process of removing the communication protocol from network boards and LAN drivers.

UNC name — Acronym for universal naming convention name, a full Windows NT name of a resource on a network. It conforms to the \\servername\sharename syntax, where servername is the server’s name and sharename is the name of the shared resource. UNC names of directories or files can also include the directory path under the share name, with the following syntax: \\servername\sharename\directory\filename.

Undersized Packet — A typical Ethernet error that occurs when the packets received are smaller than the 64 byte minimum used by Ethernet but have a good FCS (Frame Check Sequence).

Unicast datagram — An IP datagram sent to one host. See also Internet Protocol (IP); multicast datagram; broadcast datagram.

Uniform Resource Locator (URL) — An Internet standard naming convention for identifying resources available via various TCP/IP application protocols. For example, http://www.nextlev.com is the URL for our World Wide Web server site. A URL allows easy hypertext references to a particular resource from within a document or mail message. The URL also specifies the appropriate Internet protocol, such as HTTP or FTP.

Uninterruptible power supply (UPS) — See UPS.

Unipolar — A scheme used for encoding digital data in digital signals in which only a positive or negative voltage represents a data bit. This coding is used in TTY (Teletype) interfaces. Unipolar coding is susceptible to noise corruption. It is not self-clocking.

Universal Naming Convention (UNC) — A way to specify a directory on a file server. It is a multivendor, multiplatform convention for identifying shared resources on a network. Instead of referencing resources using a drive letter, which are rarely appropriate across a network, resources are referenced by the server name and share. For instance, to refer to a document called "JUNK.DOC" on a server named "BSRV1" in a directory shared as "DEPTDOCS", the UNC path would be \\BSRV1\DEPTDOCS\JUNK.DOC.

UNIX — A multitasking, Kernel-based operating system developed at AT&T in the early 1970s and provided (originally) free to universities as a research operating system. Because of its availability and ability to scale down to microprocessor-based computers, UNIX became the standard operating system of the Internet and its attendant network protocols and is the closest approximation to a universal operating system that exists. Most computers can run some variant of the UNIX operating system.

Unknown Object — A leaf object representing an indeterminable object which usually results from corruption. Unknown objects also appear when merging trees or when the Directory is not synchronized. In this case, Unknown objects should disappear after some time.

Unloading — The process of disjoining NLMs from the NetWare operating system.

UPGRADE — A NetWare 3.1x command used to upgrade the bindery, data and security on the NetWare v2.x file server to a v3.x format.

Upgrade (definition) — The conversion of a network to the NetWare 4 operating system from an earlier version NetWare or from another network operating system.

Uplink — Pertaining to data transmission from a data station to the headend. For example, a hub may have an uplink to a more central hub or router.

Upper Memory — The 384 KB of memory between 640 KB and the real mode boundary of 1 MB used for special purposes such as ROM BIOS, serial ports, adapter cards, and video.

Upper memory area — The part of physical memory that starts at 640K and ends at 1024K (hexadecimal addresses A000 through FFFF). Also called the adapter segment, because that portion of memory is often used by hardware adapters such as display adapters.

Upper memory blocks (UMB) — The unused parts of the upper memory area. For an 80386 or higher computer, information can be mapped (or copied) from another type of memory to upper memory blocks, freeing more conventional memory.

UPS — (1) Acronym for uninterruptible power supply, a battery-operated power supply connected to a computer to keep the system running during a power failure. (2) Loadable module in NetWare that provides control over the Uninterruptible Power Supply from the network file server that is attached to the file server. It can also be used to monitor the status of the UPS.

UPS Monitoring — It allows the file server to monitor an attached Uninterruptible Power Supply.

UPS service — Manages an uninterruptible power supply connected to a computer. See also UPS.

USB — Universal Serial Bus. A bidirectional, isochronous, dynamically attachable serial interface for adding peripheral devices such as game controllers, serial and parallel ports, and input devices on a single bus

USE DEFAULTS — NET.CFG parameter. By default (if ON), some VLMs are loaded automatically by the VLM.EXE.

USEnet — Service available on the Internet that enables you to exchange information with other users on the Internet on a variety of topics. For example, you can share technical information by accessing forums (bulletin boards) such as comp.sys.novell, comp.unix.unixware, etc.

User — One of three core components in Windows 95(8). It manages input from input devices, output to the user interface, and interaction with the sound driver, timer, and communications ports

User account — Consists of all the information that defines a user to Windows NT. This includes such things as the user name and password required for the user to log on, the groups in which the user account has membership, and the rights and permissions the user has for using the system and accessing its resources. For Windows NT Workstation, user accounts are managed with User Manager. For Windows NT Server, user accounts are managed with User Manager for Domains. See also group.

User account database — See directory database.

User authentication module — Software component that prompts clients for their user names and passwords. See also cleartext passwords; encrypted passwords.

User context — A user session created by an operating system in response to a logon request, and typically characterized by privilege sets that strictly define the user’s authority to access system resources and information. Contexts restrict unauthorized access to facilities and data and protect the system itself from user and applications interference, accidental or otherwise. Contexts are a feature of most multi-user operating systems, usually integrated with the security system.

User Datagram Protocol — A nonguaranteed network packet protocol implemented on IP that is far faster that TCP because it doesn’t have flow control overhead. This TCP complement offers a connectionless datagram service that guarantees neither delivery nor correct sequencing of delivered packets (much like IP). UDP can be implemented as a reliable transport when some higher level protocol (such as NetBIOS) exists to make sure that required data will eventually be retransmitted in local area environments. A See also datagram; IP; packet.

User default profile — In Windows NT Server, the user profile that is loaded by a server when a user’s assigned profile cannot be accessed for any reason; when a user without an assigned profile logs on to the computer for the first time; or when a user logs on to the Guest account. See also system default profile; user profile.

User Login Script — A login script contains commands for a specific user.

User Manager — A Windows NT Workstation tool used to manage the security for a workstation. User Manager administers user accounts, groups, and security policies.

User Manager for Domains — A Windows NT Server tool used to manage security for a domain or an individual computer. User Manager for Domains administers user accounts, groups, and security policies.

User name — A unique name identifying a user account to Windows NT. An account’s user name cannot be identical to any other group name or user name of its own domain or workgroup. See also user account.

User Object — A leaf object that represents a network user.

User password — The password stored in each user’s account. Each user generally has a unique user password and must type that password when logging on or accessing a server. See also password; volume password.

User privilege — One of three privilege levels you can assign to a Windows NT user account. Every user account has one of the three privilege levels (Administrator, Guest, and User). Accounts with User privilege are regular users of the network; most accounts on your network will probably have User privilege. See also user account; Administrator privilege; Guest privilege.

User profile — Configuration information that can be retained on a user-by-user basis, and is saved in user profiles. This information includes all the per-user settings of the Windows NT environment, such as the desktop arrangement, personal program groups and the program items in those groups, screen colors, screen savers, network connections, printer connections, mouse settings, window size and position, and more. When a user logs on, the user’s profile is loaded and the user’s Windows NT environment is configured according to that profile. See also personal groups; program item.

User rights — Define a user's access to a computer or domain and the actions that a user can perform on the computer or domain. User rights permit actions such as logging onto a computer or network, adding or deleting users in a workstation or domain, and so forth.

User rights policy — Manages the assignment of rights to groups and user accounts. See also user account; user rights.

User Template — A special User object created in a container to create default properties for new User objects in that container.

USERDEF — A NetWare 3.1x command used by the supervisor or workgroup manager to create users by using templates.

USERLIST — A NetWare 3.1x command used to list the users currently logged into the file server.

Users — In the Macintosh environment, a special group that contains all users who have user permissions on the server. When a Macintosh user assigns permissions to everyone, those permissions are given to the groups users and guests. See also everyone category; guests.

Utilities — Programs that gives more functionality to an operating system.

Utilization — The percentage of time the processor is busy.