debugger to print information about the state of the
program.
trace record. In PE, a collection of information about a
specific event that occurred during the execution of your
program. For example, a trace record is created for
each send and receive operation that occurs in your
program (this is optional and may not be appropriate).
These records are then accumulated into a trace file
which allows the Visualization Tool to visually display
the communications patterns from the program.
U
unrolling loops. See

loop unrolling

.
US. See

user space

.
user. (1) A person who requires the services of a
computing system. (2) Any person or any thing that may
issue or receive commands and message to or from the
information processing system.
user space (US). A version of the message passing
|library that is optimized for direct access to the SP
|Switch , that maximizes the performance capabilities of
the SP hardware.
utility program. A computer program in general
support of computer processes; for example, a
diagnostic program, a trace program, a sort program.
utility routine. A routine in general support of the
processes of a computer; for example, an input routine.
V
variable. (1) In programming languages, a named
object that may take different values, one at a time. The
values of a variable are usually restricted to one data
type. (2) A quantity that can assume any of a given set
of values. (3) A name used to represent a data item
whose value can be changed while the program is
running. (4) A name used to represent data whose
value can be changed, while the program is running, by
referring to the name of the variable.
view. (1) In an information resource directory, the
combination of a variation name and revision number
that is used as a component of an access name or of a
descriptive name.
Visualization Tool. The PE Visualization Tool. This
tool uses information that is captured as your parallel
program executes, and presents a graphical display of
the program execution. For more information, see
IBM

Parallel Environment for AIX: Operation and Use,

Volume 2

.
VT. See

Visualization Tool

.
X
X Window System. The UNIX industry's graphics
windowing standard that provides simultaneous views of
several executing programs or processes on high
resolution graphics displays.
xpdbx. This is the former name of the PE graphical
interface debugging facility, which is now called pedb.
Xprofiler. An AIX tool that is used to analyze the
performance of both serial and parallel applications, via
a graphical user interface. Xprofiler provides quick
access to the profiled data, so that the functions that
are the most CPU-intensive can be easily identified.
194 IBM PE for AIX V2R4.0: Messages