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`IIMIIMMINI
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`IlictioDDry of
`Coffioutillo
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`r The most comprehensive computing dictionary ever published
`v More than 181000 entries
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`SFDC 1024
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`

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`Limitation of Liability
`While the Editor and Publisher of this book have made reasonable efforts to
`ensure the accuracy and timeliness of the information contained herein, nei-
`ther the Editor nor the Publisher shall have any liability with respect to loss or
`damage caused or alleged to be caused by reliance on any information con-
`tained herein.
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`Copyright 0 1994 by International Business Machines Corporation. All rights
`reserved. Printed in the United States of America. Except as permitted under
`the United States Copyright Act of 1976, no part of this publication may be
`reproduced or distributed in any form or by any means, or stored in a data
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`2 3 4 5 6 7 8 9 0 DOC/DOC 9 9 8 7 6 5 4
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`ISBN 0-07-031488-8 (HC)
`ISBN 0-07-031489-6 (PBK)
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`The sponsoring editor for this book was Daniel A. Gonneau and the
`production supervisor was Thomas G. Kowalczyk.
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`Printed and bound by R. R. Donnelley & Sons Company.
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`Tenth Edition (August 1993)
`This is a major revision of the IBM Dictionary of Computing, SC20-1699-8,
`which is made obsolete by this edition. Changes are made periodically to the
`information provided herein.
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`international Edition
`Copyright 0 1994 by International Business Machines Corporation. Exclusive
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`

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`laser scanning power (cid:9)
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`[376]
`
`layer management
`
`laser scanning power In a laser printer, the level of
`power of a laser beam, expressed in milliwatts.
`
`last-in-chain (LIC) A request unit (RU) whose
`request header (RH) end chain indicator is on and
`whose RH begin chain indicator is off. See also RU
`chain.
`
`last-in-first-out (LIFO) A queuing technique in
`which the next item to be retrieved is the item most
`recently placed in the queue. (A)
`
`last priority level In the IBM 8100 Information
`System, the number of the most recent priority level
`that was active before dispatching the current program
`status vector.
`
`last record indicator In RPG, an indicator that
`signals when the last record (LR) is processed. This
`indicator can then be used to condition calculation and
`output operations that are to be done at the end of the
`program.
`
`latch (1) A bistable circuit that is set and reset by
`appropriate input signals. (T) See Figure 85.
`(2) In IMSNS, a programming device that provides
`short-term serialization for IMS/VS tasks running in
`the online IMS/VS system. An IMS/VS latch is
`similar in function to an OS/VS lock. (3) An elec-
`tronic circuit that records the status of a signal until it
`is reset.
`
`Figure 85. Latch
`
`latch-di .. a key On a typewriter, a control that, when
`operated, is maintained in its position until it is
`released. (T)
`
`latch-out tabulator key On a typewriter, a tabulator
`key that can be released before the tabulator stop posi-
`tion has been reached without affecting operation of
`the stop. (T) Synonymous with touch tabulator key.
`
`latency (1) The time interval between the instant at
`which an instruction control unit initiates a call for
`data and the instant at which the actual transfer of the
`data starts. Synonymous with waiting time. See
`Figure 3. (T) (2) The time required for the light
`emitted from the phosphor on a display screen to
`decay after the excitation is removed. Long-
`persistence phosphors create less flicker of still
`images, but more blurring of moving images. (3) See
`also ring latency.
`
`latent image In a document copying machine, the
`invisible image that exists in the sensitized material
`after exposure but before development. (T)
`
`lateral redundancy check Synonym for transverse
`redundancy check.
`
`Latin font Synonym for single-byte coded font.
`
`lattice See computer security model.
`
`lavalier A small microphone usually worn on the
`lapel. Synonymous with lapel mike.
`
`layback In video production, the process used by a
`production facility of combining dialog or sound with
`a score.
`
`layer (1) In network architecture, a group of services
`that is complete from a conceptual point of view, that
`is one out of a set of hierarchically arranged groups,
`and that extends across all systems that conform to the
`network architecture. (T) See application layer, data
`link layer, network layer, physical layer, presentation
`layer, session layer, transport layer. (2) In the Open
`Systems Interconnection reference model, one of seven
`conceptually complete, hierarchically arranged groups
`of services, functions, and protocols, that extend
`across all open systems. (T) (3) In SNA, a
`grouping of related functions that are logically sepa-
`rate from the functions in other layers. Implementa-
`tion of the functions in one layer can be changed
`without affecting functions in other layers. See data
`flow control layer, data link control layer, path control
`layer, physical control layer, presentation services
`layer, transaction services layer, transmission control
`layer. (4) For local area networks, see logical link
`control (LLC) sublayer, medium access control (MAC)
`sublayer. (5) In DPPX, a predefined subset of
`modules or programs having related functions that can
`be replaced or modified without affecting other layers.
`
`layering In music or sound production, the technique
`of combining many sound generators to create a richer
`sound.
`
`layer management Functions, such as activation and
`error control, related to the management of a specific