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UA. See unnumbered acknowledge.

UART. See Universal Asynchronous Receive/Transmit.

ublock. See user block.

UCT. See Universal Coordinated Time.

UDP. See User Datagram Protocol.

UDP/IP. User Datagram Protocol/Internet Protocol.

UFS. See UNIX File System.

UI. See unnumbered information frame.

UID. See user number and AIXwindows User Interface Definition.

UIL. See AIXwindows User Interface Language.

ultimate consumer. The target of data in an input and output operation. An ultimate consumer can be a file, a device, or an array of bytes in memory.

ultimate producer. The source of data in an input and output operation. An ultimate producer can be a file, a device, or an array of bytes in memory.

umask. The file-mode creation mask. The default permissions that are set automatically when a file is created. These defaults can be changed by including an appropriate umask command in the system profile.

unary expression. An expression that contains one operand.

unary operator. An operator that represents an operation on one operand. Contrast with binary operator.

unblocked. In an Enterprise Systems Connection Director, the attribute that, when set, establishes communications capability for a specific port. Contrast with block.

unconditional branch. A branch that is taken every time it is encountered.

unconfigure. (1.) Indicates that a user is taking a device from the available (configured) state to the defined state. This is accomplished by running the unconfigure method for a device. The device status field in the Customized Devices Object Class would reflect this action. (2.) To take out of use by the current computer system.

undefine. (1.) Indicates that a user is taking a device instance out of the system. This is accomplished by running the undefine method for the device. All information for the device in the Customized Database is purged by this operation. (2.) To cause a command to no longer recognized by the current computer system.

underlying editor. A large editor program, such as vi, of which another editor program, such as vedit, is a limited subset.

unescaped. In an expression, a character that is not preceded by an escape sequence and is therefore interpreted as a control character. See also escape sequence.

unformatted file. A file displayed with data that is not arranged with particular characters.

unidirectional printing. A printing method in which the print head on the printer prints only while it moves in one direction, instead of also printing while it moves in the opposite direction. This method of printing usually produces higher-quality print output.

union. A variable that can hold any one of several data types, but only one data type at a time.

union tag. The identifier that names a union data type.

uniprocessor. A system containing a single processor. As used in this book, the phrase "comparable uniprocessor" means a system designed to have only a single processor, with the same CPU-clock speed and cache capacity as the SMP system being discussed, running a uniprocessor version of the operating system. Contrast with single-processor SMP system.

unit. (1.) In FORTRAN, a means of referring to a file to use input/output statements. A unit can be connected or not connected to a file. If connected, it refers to the file. The connection is symmetric; that is, if a unit is connected to a file, the file is connected to the unit. (2.) See also compilable unit. (3.) For Ada programming, synonym for compilation unit.

unit cube. In GL, a volume defined by the following planes: x = -1, x = 1, y=-1, y = 1, z = -1, z=1. See also normalized device coordinates.

unit identifier. In FORTRAN, the number that specifies an external unit or internal file. The number can be one of the following: (1.) an integer expression whose value must be zero or positive, (2.) an * (asterisk) that corresponds to unit 5 for input or unit 6 for output, or (3.) the name of a character array, character array element, or character substring for an internal file.

Universal Asynchronous Receive/Transmit. A circuit used in asynchronous data communication applications to provide all the necessary logic to recover data in a serial-in parallel-out fashion and to transmit data in a parallel-in serial-out fashion. It is usually full-duplex, that is, it can transmit and receive simultaneously with the option to handle various data work length.

Universal Coordinated Time (UCT). The new standard term for worldwide time-telling that has the same meaning as Greenwich Mean Time.

Universal Unique Identifier (UUID). A 128-bit value used for identification. NCS uses UUIDs to identify cells, interfaces, objects, and types. The UUID for a cell, generated by the uuid_gentool, is completely unique, having been created based on the unique system ID of the workstation and a time stamp. Once generated, the cell UUID is placed in the glb_obj.txt file. See also object UUID and type UUID.

UNIX File System (UFS). A section of the UNIX file tree that is physically contained on a single device or disk partition and that can be separately mounted, dismounted, and administered.

UNIX-to-UNIX Copy Program (UUCP). (1.) A group of commands, programs, and files, present on most UNIX systems, that allows the user to communicate with another UNIX system over a dedicated line or a telephone line. See also Basic Networking Utilities. (2.) The command (uucp) that starts file copying from one or more sources to a single destination.

unmanaged widget. A widget whose size cannot be changed.

unmapped window. A window that is not visible on the screen.

unmarshal. In NCS, to copy data from a Remote Procedure Call packet. Stubs perform unmarshalling. Contrast with marshal.

unnumbered acknowledge (UA). A link control frame.

unnumbered information (UI) frame. A frame in unnumbered format, used to transfer unnumbered control functions.

unpredictable. A violation of an architecture rule that an implementation is not required to report. Results can include an error report from a threads call, the operating system, or the hardware; a hang or deadlock of the program; or an incorrect operation of the program without indication of error. See also illegal.

unprivileged state. A hardware protection state in which the processor can only run unprivileged instructions. The processor's unprivileged state supports the virtual machine's operating system state and problem state. Contrast with privileged state.

unreachable code. Code that cannot be reached during program execution. Unreachable code is detected and removed as part of optimization.

unused subprograms. In Ada language, subprograms unused only within the context of a specific program or set of units. For example, a program might call only a small subset of subprograms in a utility package. The remaining uncalled (unreachable) subprograms constitute unreachable code in the context of that program.

unviewable. Pertaining to a mapped window with an unmapped ancestor.

update. (1.) The procedure of modifying a program or program option that exists on the mass storage medium of a computer, making the program executable, and ensuring that the modified program interacts properly with all other affected programs in the system. (2.) An improvement for some part of the system. (3.) To add, change, or delete items. (4.) To modify a master file with current information according to a specified procedure.

update propagation. An immediate attempt to apply a change to all replicas of the CDS directory in which the change was just made. An update propagation delivers changes in a more efficient and timely way than a skulk, which is the periodic distribution of a whole collection of changes.

update script. A shell script or executable file created by the developer of an application program to update the program. The script file must follow specific guidelines to be compatible with the program update tools that are provided in the operating system.

Update Timestamp (UTS). An attribute that identifies the time at which the most recent change was made to any attribute of a particular CDS name. For directories, the UTS reflects changes made only to attributes that apply to the directory as a whole (not one of its replicas).

upgrade. Software that fixes a defect in a previously released software product.

upgrade locks. Locks used instead of read locks that announce the potential need to also modify the protected data. If an application obtains a read lock and possibly a write lock to the same data, an upgrade lock is less likely to deadlock.

upload. To transfer data from one computer to another. Typically, users upload from a small computer to a larger one.

upstream. The direction from driver to stream head.

usage bindings. The language-specific binding files for a class that are generated by the SOM Compiler for inclusion in client programs using the class.

use clause. In Ada language, a clause that achieves direct visibility of declarations that appear in the visible parts of named packages.

use-once license. In License Use Management, a type of license administrated by the license server that can be used for a single instance of invoking a product or of using a service. The license server decrements the number of use-once licenses each time the product is used.

user. (1.) The name associated with an account. (2.) Anyone requiring the services of a computing system.

user account. See account.

user address list. The address list that an individual can use with the xtalk command to make outgoing X.25 calls. See also address list and system address list.

user area. The parts of main storage and disk available to the user.

user block. A data structure maintained by the kernel that contains system information about a user process, such as its real and effective user IDs, the list of open file descriptors, and signal-handling settings. The user structure (defined in the /usr/include/sys/user.h header file) specifies the exact information that is kept in the user block. See also per-process data area.

User Datagram Protocol (UDP). A packet-level protocol built directly on the Internet Protocol layer. UPD uses application-to-application programs between host systems.

user data segment. In kernel mode, the virtual memory segment that contains user data, which consists of initialized data variables.

user-defined variable. A shell variable to which the user assigns a character string as a value.

user file. A text file that specifies the users who may (or may not) use licensed software products.

user ID. See user identification.

user identification (user ID). (1.) One to eight alphanumeric characters, beginning with an alphabetic, #, $, or > character, that identifies a user. This string of characters limits the functions and information the operator can use. Often, the user ID can be substituted in commands that take a user's login name as a value. See also user number. (2.) A parameter that specifies the user ID under which the application or transaction program runs. Contrast with user name.

user interface. The hardware, software, or both by which a user communicates with a system, program, or device. Examples are a keyboard, mouse, command language, or windowing subsystem.

user mode. A mode in which a process is carried out in the user's program rather than in the kernel. Contrast with kernel mode.

user name. A string of characters that uniquely identifies a user to the system. Contrast with user identification.

user number (UID). A number that uniquely identifies a user to the system. It is the internal number associated with a user ID. See also user identification (user ID).

user profile. A file in the user's home directory named .profile that contains shell commands that set initial user-defined characteristics and defaults for the login session.

user space. The address space seen by a process in user mode. See also user structure.

user structure. In kernel mode, the data area that contains information that must be accessible while a process runs. One user structure is allocated for each active process. See also per-process data area and user block.

user time. The amount of time a program is running in the CPU. Does not include time associated with operating system services provided to the program, the program's I/O time, or time in which other processes preempt the program's use of the CPU.

USOC-RJ11. A miniature telephone jack.

UTC. See Universal Coordinated Time.

utility. (1.) A service. In programming, a program that performs a common service function. (2.) The capability of a system, program, or device to perform the functions for which it is designed.

UTS. See Update Timestamp.

UUCP. See UNIX-to-UNIX Copy Program.

UUCP login ID. A login name, provided with the Basic Networking Utilities (BNU), that has complete access to all BNU files and directories. See also Basic Networking Utilities.

UUID. See Universal Unique Identifier.

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