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`9TH EDITION
`
`0SBORNEffil
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`1
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`

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`c:omputer
`DesKtop
`Encyclopedia
`
`Ninth Edition
`
`Alan Freedman
`
`Osborne/McGraw-Hill
`New York Chicago San Francisco
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`2
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`Osborne/McGraw-Hill
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`please contact Osborne/McGraw-Hill at the above address. For information on
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`Contact Information page at the end of this book.
`
`Computer Desktop Encyclopedia, Ninth Edition
`
`Copyright© 2001 by The McGraw-Hill Companies. All rights reserved. Printed in the
`United States of America. Except as permitted under the 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 database or retrieval system, without the prior written permission of the
`publisher, with the exception that the program listings may be entered, stored, and
`executed in a computer system, but they may not be reproduced for publication.
`
`1234567890 DOC DOC 901987654321
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`Book p/n 0-07-219307-7 and CD p/n 0-07-219308-5
`parts of
`ISBN 0-07-219306-9
`
`Publisher
`Brandon A. Nordin
`
`Vice President & Associate Publisher
`Scott Rogers
`
`Computer Designers
`Lauren McCarthy, Tabitha Cagan
`
`Illustrators
`Lyssa Wald, Michael Mueller
`
`Editorial Director
`Roger Stewart
`
`Senior Project Editor
`Pamela Woolf
`
`Proofreaders
`Linda Medoff, Paul Medoff
`
`Series Design
`Peter F. Hancik
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`Cover Design
`Greg Scott
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`Cover Illustration
`John Bleck
`
`This book was composed with Corel VENTURA™ Publisher.
`
`Information has been obtained by Osborne/McGraw-Hill from sources believed to be reliable. However, because of the
`possibility of human or mechanical error by our sources, Osborne/McGraw-Hill, or others, Osborne/McGraw-Hill does not
`guarantee the accuracy, adequacy, or completeness of any information and is not responsible for any errors or omissions or
`the results obtained from use of such information.
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`handle
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`Half-inch reels evolved into half-inch, self-threading tape cartridges, including
`IBM's 3490/3490/3590 line, Quantum's DLT and StorageTek's Redwood, which hold
`from 800MB to 50GB. See Magstar, DLT, Redwood and magnetic tape.
`
`halftone
`In printing, the simulation of a continuous-tone image (shaded drawing,
`photograph) with dots. All printing processes, except for Cycolor, print dots. In
`photographically generated halftones, a camera shoots the image through a halftone
`screen, creating smaller dots for lighter areas and larger dots for darker areas. Digitally
`composed printing prints only one size of dot.
`In order to simulate variable-sized halftone dots in computer printers, dithering is
`used, which creates clusters of dots in a "halftone cell." The more dots printed in the
`cell, the darker the gray. As the screen frequency gets higher (more cells per inch), there
`is less room for dots in the cell, reducing the number of shades of gray or color that can
`be generated.
`In low-resolution printers, there is always a compromise between printer resolution
`( dpi) and screen frequency (!pi), which is the number of rows of halftone cells per inch.
`For example, in a 300 dpi printer, the 8x8 halftone cell required to create 64 shades of
`grays results in a very coarse 38lines per inch of screen frequency (300 dpi divided by 8).
`However, a high-resolution, 2,400 dpi imagesetter can easily handle 256 shades of gray
`at 150 lpi (2,400/16).
`
`Open Reel Tape
`Although organizations have
`migrated to cartridge formats,
`legacy applications remain that
`still use open reels.
`
`PRINTER RESOLUTION & MAXIMUM SCREEN FREQUENCY
`
`Analog halftone dots
`
`Digital halftone cells
`
`Shades
`At Printer Resolutions:
`Cell of gray
`size or cols 300 dpi 1,200 dpi 2,400 dpi
`
`16
`4x4
`64
`8x8
`l6xl6 256
`
`150 lpi
`38 lpi
`19 lpi
`
`300 lpi
`130 lpi
`75 lpi
`
`600 lpi
`300 lpi
`150 lpi
`
`hammer
`(1) In a printer, the mechanism that pushes the typeface
`onto the ribbon and paper or pushes the paper into the ribbon and
`typeface.
`(2) (Hammer) The code name for AMD's next-generation, 64-bit
`CPU chips. Expected in 2001, the Sledgehammer is one of the CPU
`models in the line. See Athlon and Itaniurn.
`
`Analog vs. Digital
`. The analog world of commercial printing prints
`dots in varying sizes. The digital world prints in
`grids of dots. Increasingly, digital printers use
`techniques that overlap dots to achieve greater
`variability in dot sizes.
`
`Hamming code An error correction method that intersperses three check bits at the end of each four data bits. At
`the receiving station, the check bits are used to detect and correct one-bit errors automatically.
`
`hand coding Writing in a programming language. Hand coding in assembly language or in a third-generation
`language, such as COBOL or C, is the traditional way programs have been developed. In contrast, visual programming
`tools allow full applications or parts of an application to be developed without writing lines of programming code.
`
`handheld computer A computing device that can be easily held in one hand while the other hand is used to
`operate it. The Palm devices are a popular example. See Palm, smart phone and palmtop.
`
`handheld scanner A scanner that is moved across the image to be scanned by hand. Handheld scanners are
`small and less expensive than their desktop counterparts, but rely on the dexterity of the user to move the unit across
`the paper. Trays are available that keep the scanner moving in a straight line. Contrast with flatbed scanner, sheet1ed
`scanner and drum scanner.
`
`handle
`
`(1) In computer graphics, a tiny, square block on an image that can be grabbed for reshaping.
`
`1.:
`,•jl
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`I
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`Computer Desktop Encyclopedia
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`P DIP
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`745
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`PDA
`(Personal Digital Assistant) A handheld computer that serves as an
`organizer for personal information. It generally includes at least a name and address
`database, to-do list and note taker. PDAs are pen based and use a stylus to tap
`selections on menus and to enter printed characters. The unit may also include a small
`on-screen keyboard which is tapped with the pen. Data is synchronized between the
`PDA and desktop computer via cable or wireless transmission.
`A PDA is like a palmtop computer except that the PDA typically uses a pen
`whereas the palmtop uses a small keyboard. Apple's MessagePad, more commonly
`known as the "Newton," was the first to popularize the concept. See Palm.
`
`PDC
`(1) (Primary Domain Controller) A Windows NT service that manages
`security for its local domain. Every domain has one PDC, which contains a
`database of usernames, passwords and permissions. See BDC.
`(2) (Personal Digital Communications) A digital cellular phone system widely
`used in Japan. Based on TDMA, it transmits in the 810-826MHz and 1,477-1,501MHz
`bands. PDC is a 2G wireless system. See wireless generations and PHS.
`
`PD disk
`(Phase change Dual disk) A rewritable optical disk from Panasonic that
`uses phase change technology. futroduced in 1995, it uses 5.25" cartridges that hold
`650MB and can withstand 500,000 rewrites. The PD drive also reads CD-R OMs, and
`the drive tray accomodates both PD cartridges and CD-ROM discs. The drive does
`not support Panasonic's earlier 5.25" phase change (PCR) cartridges. Panasonic's
`DVD-RAM drives also read and write PD disks. See phase change and optical disk.
`
`The Newton
`Although latertaken off the market,
`Apple's Newton pioneered the PDA
`concept. (Image courtesy of Apple
`Computer, Inc.)
`
`PDES
`(Product Data Exchange using STEP) A standard format
`for exchanging data between advanced CAD and CAM programs. It
`describes a complete product, including the geometric aspects of the
`images as weU as manufacturing features, material properties and
`tolerance and finish specifications. For more information, visit
`http:/ /pdesinc.aticorp.org. See IGES.
`
`PDF
`(Portable Document Format) The page description language
`used in the Acrobat document exchange system. See Acrobat and
`extension.
`
`PDF41. 7
`(Portable Data File417) A two-dimensional bar
`code developed by Symbol Technologies, fuc., Bohemia, NY,
`(www.symbol.com). Created in the late 1980s, the standard was later
`placed in the public domain and is governed by the Automatic
`Identification Manufacturers (AIM) trade association. PDF417 is the
`most widely used 2-D bar code (more than one row of codes), and it can
`hold up to 1,800 bytes of any digital data in a printed area about the size
`of a business card. For bills of lading and applications that require more
`information, multiple bar codes can be printed. The scanner, which is
`made by Symbol Technologies and other companies, reads the bar code
`horizontally and vertically. MicroPDF417 is a denser version of PDF417
`that takes up less space. It is used for marking small parts and can hold
`up to 300 bytes.
`
`PD Cartridge
`The PD cartridges look like and use the same
`technology as DVD-RAM disks. Panasonic's
`DVD-RAM drives read and write PD cartridges.
`
`PDIAL
`(Public Dialup Internet Access List) A list of Internet service
`providers (ISPs) maintained by Peter J!:aminsky. The last available
`PDIAL list is on various Web sites.
`
`The Gettysburg Address
`This PDF417 image contains the entire
`Gettysburg address. (Image courtesy of Symbol
`Technologies, Inc.)
`
`PDIP
`
`(Plastic DIP) See DIP.
`
`Computer Desktop Encyclopedia
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`5
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