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retention period:
The length of time for which data on a data medium is to be preserved.

retina laser:
A laser system that projects images directly on the retina.

(1) In information processing, the act or process of recovering data or information. (2) In a conceptual schema language, the making known of a sentence that has been inserted into the information base or conceptual schema, or that is deducible from other sentences in the information base or conceptual schema. (3) In electronic mail, a transmittal step in which a message or report is extracted from the user's message store and conveyed to the user's user agent. This user is an actual recipient.

retrieval code:
In micrographics, a code used for manual or automatic retrieval of microimages.

retrieval function:
In a data manipulation language, a capability to select and to locate stored records with specified characteristics and to transfer these records to a working space for any required further processing by application software.

retrospective trace:
A trace produced after execution of a program has ended, from historical data recorded during the execution. A retrospective trace differs from an execution trace which is produced cumulatively during execution.

(1) To execute a return statement that causes a jump to the calling program. (2) To provide a data value to the calling program when executing a return statement.

return code:
A code that is used to influence the execution of subsequent instructions.

return from a procedure:
A language construct within a procedure designating an end of an execution sequence in the procedure.

return statement:
A language construct within a module that designates the end of an execution sequence (or possibly several such sequences) in that module and causes a jump to a specified point in the calling module, and possibly provides a result to it.

return-to-reference recording (RRR):
The recording of bits such that a 1 (or a 0) is recorded as a pulse with a return to a reference condition between pulses. Contrast with nonreturn-to-reference recording.

return-to-zero recording (RZR):
Return-to-reference recording in which the reference condition is the zero value. (Figure 56 - Return-to-zero recording).

reverse clipping:
Synonym for shielding.

reverse direction flow:
In flowcharting, a flow in a direction other than left to right or top to bottom.

reverse find:
Synonym for backward search.

reverse LAN channel:
Synonym for backward LAN channel.

reverse Polish notation:
Synonym for postfix notation.

reverse printer:
Synonym for bidirectional printer.

reverse search:
Synonym for backward search.

reverse video:
The modification of a display image or a portion thereof by inverting background and foreground colors or shades, usually for highlighting purposes.

revision number:
In an information resource dictionary, a nonnegative integer that is a component of the version identifier of the access name of an entity and that is assigned consecutively to each change that affects the entity.

To bring a tape back to its starting position. By extension, the verb rewind is also used for logically establishing file reference as if rewinding a tape.

rewritable optical disk:
An optical disk in which the data in specified areas can be rewritten by an optical beam.

Request for Comments.

rich media:
Data, where text, graphics, video, or voice are linked for easy transition from one medium to another.

rich text:
ASCII text that has been embellished by the inclusion of such things as embedded fonts, graphics, and audio.

right adjusted:
Synonym for right-justified.

Synonym for right-justified.

right-hand side:
The set of propositions or statements in the "then" part of an if-then rule.

In text processing, pertaining to text that is aligned to the right margin but need not be aligned to the left margin. Synonymous with flush-right, right adjusted, right-aligned.

To shift the contents of a register or of a field so that the significant character at the right-hand end of the data is at a particular position.

Synonym for ring network.

ring latency:
In a ring network, the time required for a signal to propagate once around the ring. The ring latency includes the signal propagation delay through the ring medium, including drop cables, plus the sum of propagation delays through each data station connected to the token-ring network and is related to the data transmission rate.

ring mouse:
A small mouse that is worn around a finger and that can be operated by a thumb or another finger.

ring network:
A network in which every node is an intermediate node with exactly two branches connected to it. Synonymous with ring. (Figure 43 - Network topologies).

reduced-instruction-set computer.

RISC processor:
A processor that employs a small number of simple instructions that are used together to perform more powerful operations, to reduce the number of clock cycles per instruction. Because of the instruction simplicity and the use of large number of registers, each generally takes only one clock cycle to execute, and the processor can run at higher speeds than can most complex instruction set computer processors. Synonymous with reduced instruction set computer processor.

rise time:
In the approximation of a step function, the time required for a signal to change from a specified low value to a specified high value. Usually these values are 10% and 90% of the step height.

In security, the possibility that a particular threat will exploit a particular vulnerability of a data processing system. (Figure 57 - Risk).

risk acceptance:
A managerial decision to accept a certain degree of risk, usually for technical or cost reasons.

risk analysis:
A systematic method of identifying the assets of a data processing system, the threats to those assets, and the vulnerability of the system to those threats. Synonymous with risk assessment.

risk assessment:
Synonym for risk analysis.

remote job entry.

(1) A usually programmable mechanical device designed to perform tasks of manipulation or locomotion under automatic control. (2) The software analogue of a mechanical robot that can move around a network, sometimes called a bot; for example, a knowledge robot.

The branch of technology concerned with designing, building, and using robots.

robot system:
A manufacturing cell, including the robot hardware and software, consisting of the manipulator, the power supply, the control system, the end effectors, and including any equipment with which the robot is interfacing and any communications interface that is operating and monitoring the robot.

robot vision:
Machine vision that provides visual data for feedback to or guidance of a robot.

The degree to which a functional unit can function correctly in the presence of invalid input or stressful environmental conditions.

region of interest.

(1) The restoration of a database to its state at a prior, specified point in time. (2) A programmed return to a prior checkpoint.

roll in:
To transfer a set of data, such as files or programs, from external storage to main memory for use.

Scrolling restricted to an upward or downward direction. Synonymous with vertical scrolling.

roll out:
To transfer a set of data, such as files or programs from main memory to external storage for the purpose of freeing main memory.

rollover windowing:
Synonym for window cascading.

read-only memory.

The highest level of a hierarchy.

root compiler:
A compiler that compiles into an intermediate language only. A root compiler, when combined with a code generator, comprises a full compiler.

root node:
A node that has no parent node.

remote operations service element.

In computer graphics, revision of display elements so as to represent the turning of an object around a fixed axis.

rotational delay:
Synonym for search time.

rotational position sensing (RPS):
A technique for continuously monitoring a disk position to indicate the position currently available for reading and writing by continuously comparing the read/write head position with appropriate synchronization signals.

rotational sweep:
A sweep representation created by moving a two-dimensional area about an axis; for example, to represent a torus or doughnut by moving a circle about an axis.

rote learning:
A learning strategy that consists in directly accumulating new knowledge without any inference being performed on the information provided. Rote learning includes learning by direct memorization of given concept descriptions and learning by being programmed.

In a positional representation, to delete or omit one or more of the least significant digits and to adjust the part retained in accordance with some specified rule. The purpose of rounding is usually to limit the precision of the numeral or to reduce the number of characters in the numeral, or to do both these things. The most common arithmetic forms of rounding are rounding down, rounding up, and rounding off.

round down:
To round, by making no adjustment to the part of the numeral that is retained. If a numeral is rounded down, its absolute value is not increased. Rounding down is a form of truncation; for example, the numerals 12.6374 and 15.0625, when rounded down to two places, become 12.63 and 15.06, respectively.

round-down function:
The function that allows the elimination in the result of the calculation of all digits beyond the least significant digit.

rounding error:
An error due to the deletion or omission of one or more of the least significant digits in a positional representation.

round off:
(1) To round, by adjusting the part of the numeral retained by adding 1 to the least significant of its digits and executing any necessary carries, if and only if the most significant of the digits deleted was equal to or greater than half the radix of its digit place; for example, the numerals 12.6375 and 15.0625, when rounded off to two places, become 12.64 and 15.06, respectively. (2) To round, by adjusting the part of the numeral retained by adding one to the least significant of its digits and executing any necessary carries if:
  1. the most significant of the digits deleted was greater than half the radix of that digit place;
  2. the most significant of the digits deleted was equal to half the radix and one or more of the following digits were greater than zero;
  3. the most significant of the digits deleted was equal to half the radix, all the following digits were equal to zero, and the least significant of the digits retained was odd.
For example, the numerals 12.6375 and 15.0625, when rounded off to three places, become 12.638 and 15.062, respectively. In this definition, "even" may be substituted for "odd."

round-off function:
The function that allows the adding of one to the least significant digit in the result of a calculation together with the necessary carries, where the subsequent digit in the result is 5 or above; where the subsequent digit is 4 or below, the least significant digit remains unchanged.

round-trip propagation time:
Twice the time required for a bit to travel between the two most distant data stations in a network. In a network using carrier sense, each frame must be long enough so that a collision or a jam signal may be detected by the transmitting data station while this frame is being transmitted. The minimum length of a frame is, therefore, determined by the round-trip propagation time.

round up:
To round, by adjusting the part of the numeral that is retained by adding 1 to the least significant of its digits and executing any necessary carries, if and only if one or more nonzero digits have been deleted. If a numeral is rounded up, its absolute value is not decreased; for example, the numerals 12.6374 and 15.0625, when rounded up to two places become 12.64 and 15.07, respectively.

round-up function:
The function that allows the adding of 1 to the least significant digit in the result of a calculation together with the necessary carries, if any of the highest places dropped off has a value of more than zero.

A functional unit that establishes a path through one or more computer networks. In computer networks conforming to the OSI model, a router operates at the network layer.

A program, or part of a program, that may have some general or frequent use.

The process of determining the path to be used over a network for the transmission of a signal or a message.

A horizontal arrangement of characters or other expressions.

row pitch:
The distance between corresponding points of adjacent rows measured along a track.

remote procedure call.

An early commercially oriented high-level programming language used to generate reports. RPG is the abbreviation for Report Program Generator.

rotational position sensing.

return-to-reference recording.

The record separator character.

reliable transfer service element.

In computer graphics, the result of moving a set of points in a manner that preserves interconnectivity with other points through stretching, shrinking, or reorienting their interconnecting lines.

rule-based synthesis:
A method of speech synthesis based on the conversion of a phonetic description to parameters of a speech-production model by means of a set of rules.

rule-based system:
A computer system that applies if-then rules to expressions to produce new expressions. In artificial intelligence, the expressions may be propositions. Synonymous with production system.

rule matching:
In artificial intelligence, the matching of the goal and the elements of a given problem by cascaded application of a series of if-then rules.

ruler line:
A line that indicates where the left and right margins and any tab stops are set.

A performance of one or more jobs or programs.

run-length encoding:
The process of encoding a digital data stream, which defines that stream in terms of the number of successive digital data elements that have the same value. For example, digital encoding in which each sequence of pixels having the same shade of gray is represented as a value of magnitude and a value of length.

Pertaining to the task state of an executable task in which the task is currently assigned to a processor. (Figure 58 - State transition diagram).

running foot:
Synonym for page footer.

running head:
Synonym for page header.

run stream:
Synonym for job stream.

run time:
Synonym for execution time.

runtime object:
In hypermedia, a hyperobject created from a model at execution time.

run unit:
An execution of one or more programs as a unit.

R/W disk:
A type of optical disk that provides for data to be written, read and erased many times using thermo-magnetic and magneto-optical effects or using the phase change recording and read-out method.

return-to-zero recording.

polarized return-to-zero recording.

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