Barrons Publishing Dictionary of Computer and Internet Terms 10th
.pdfvision, human |
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are constant, such as identifying objects that pass by on an assembly line and sounding an alarm when one of them is missing or looks abnormal.
See also
vision, human the ability to see. Computer displays rely on many special properties of human vision, among them the following:
1.The eye blends together images that are less than 1⁄30 second apart. For flicker-free viewing, the computer must scan the screen at least 30 and preferably more than 70 times per second.
2.Movements that are made in steps lasting 1⁄30 second or less appear to be continuous. A moving image is actually a series of still images presented in very rapid succession.
3.Colors can be simulated by mixing other colors. For example, yellow on a computer screen does not contain any yellow light; instead, it is a mixture of red and green light. See COLOR.
Working with a computer screen can be tiring to the eyes, especially if the display is blurry or glare is a problem, but no permanent harm results. Eyeglasses designed for the proper working distance can make computer work much easier. See EYEGLASSES,
COMPUTER.
vision, machine see VISION, COMPUTER.
visit the occurrence of one web browser requesting documents (WEB PAGEs) from a site during a short period of time. A single visit to a web site may generate several HITs.
Vista see WINDOWS (MICROSOFT).
Visual Basic one of the first successful interactive development environments for Windows programming, introduced by Microsoft in 1991. Programmers can lay out the program’s windows graphically (Figure 290) and write BASIC code to specify what happens when each button is clicked or other events occur. Any part of the layout or code can be changed at any time. Unlike in earlier Windows programming environments, the programmer need not write any general code to initialize windows, handle events, or interact with the operating system.
The current version is called Visual Basic .NET or VB.NET and uses the .NET Framework for fully object-oriented programming. Similar products for other programming languages include Microsoft’s Visual C++ and Visual C# and Borland’s Delphi and Kylix (for Pascal), JBuilder (for Java), and C++ Builder.
See also EVENT-DRIVEN PROGRAMMING; .NET FRAMEWORK; OBJECTORIENTED PROGRAMMING.
visual chat a CHAT ROOM or similar online conversation where, in addition to chat handles (names), users are represented by graphics.
Visual Studio development environment provided by Microsoft for Visual Basic, C++, C#, and other languages.
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void |
FIGURE 290. Visual Basic
visualization
1.in scientific computing, the science and art of making information visible through graphs, charts, and animation.
2.in audio playback programs, a way of creating visual images that move with the sound being played, such as waveforms, spectra, or abstract effects.
VLSI (very large-scale integration) the manufacture of integrated circuits (silicon chips) containing 10,000 or more logic gates.
VM see JVM; VIRTUAL MACHINE.
VM/CMS see CMS; VM/ESA.
VM/ESA (Virtual Machine/Enterprise Systems Architecture) an operating system for large IBM mainframe computers, such as the 370, 3081, and 390, based on the idea of one computer simulating multiple copies of itself. VM/ESA was formerly known as VM/SP. (See also MVS; TSO.)
voice chat an audio conversation or conference with multiple participants, transmitted by computer network. Compare VIDEOCONFERENCING.
voice mail messages that are received by telephone, recorded, and played automatically when the recipient requests them. Voice mail systems are computer-controlled; messages are saved in digital form.
voice recognition
1. the recognition of spoken words by a computer. See NATURAL LANGUAGE PROCESSING.
2. the identification of people by computers that recognize the distinctive characteristics of their voices. See BIOMETRICS.
void in C and related programming languages, a keyword that means “no data type” and declares a function or method that returns no value or a pointer to an unknown type.
VoIP |
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VoIP (Voice over Internet Protocol) the transmission of voice telephone conversations through the Internet or through IP networks. Several protocols are used for this purpose. See INTERNET TELEPHONY; PROTOCOL;
SKYPE.
voken (virtual token) an advertisement that appears over the contents of a browser window, but not in a window of its own. Compare POP-UP AD.
The voken can move around the screen, rotate, and blink to attract attention. A moving voken can trick you into clicking on it—thus going to the advertiser’s site—when you meant to click on something else, but it got in the way.
volatile not permanent; erased when turned off. The memory (RAM) of a computer is volatile; that is, it goes blank when power is removed. Flash memory and disks are non-volatile. In some programming languages, a variable is declared volatile if it can be changed by something outside the program.
volt the unit of measure of electric potential. If a potential of 1 volt is applied to a resistance of 1 ohm, then a current of 1 ampere will flow through the resistance. (See OHM’S LAW.)
volume
1.an individual diskette, disk, or tape.
2.the perceived loudness of a sound. The volume control on a sound card may be a knob on the card itself, a setting made in software, or both.
volume serial number an identifying number assigned to a disk or tape by Windows or other operating systems. Volume serial numbers ensure that the computer will know when the disk or tape in a drive is changed.
Von Neumann architecture a type of computer design in which programs and data are stored in a single kind of memory. Contrast
TECTURE. See COMPUTER ARCHITECTURE.
Von Neumann, John (1903–1957) mathematician who worked on one of the earliest computers and developed the concept of storing programs in memory.
voxel (from volume cell) one of the cubes into which a three-dimensional space is divided, like a PIXEL but in three dimensions.
VPN (virtual private network) a network where data is transferred over the Internet using security features preventing unauthorized access.
VRAM (video random access memory) RAM that is specially designed for use in video cards. Commonly, it can be read and written simultaneously so that the generation of the display is not interrupted when the CPU needs to place data in it.
VRML (Virtual Reality Markup Language or Virtual Reality Modeling Language) a programming language developed by Mark Pesce and Tony Parisi to describe three-dimensional objects for graphical display. A
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VRML |
VRML program describes a “world” of virtual objects that a person can walk or fly through. The computer draws the objects as they are seen from a specified position, which can be constantly changing. Objects can respond to mouse clicks.
Figure 292 shows a sample program written in VRML 1.0 (1996). It depicts a sphere and three blocks in front of a large black panel. In the language, a “separator” is an object composed of one or more primitive shapes. Figure 291 shows this scene as viewed from two different angles with a VRML BROWSER (viewing program). More sophisticated VRML programs can provide very realistic views of scenery and buildings. The successor to VRML is X3D.
FIGURE 291. VRML example, displayed two ways
#VRML V1.0 ascii
Separator { Separator {
# Black panel
Transform { translation 0 0.1 -0.5 } Material { diffuseColor 0 0 0 }
Cube { width 1.2 height 0.65 depth 0.5 }
}
Separator {
# Ball
Transform { translation 0 0.2 0 } Material { diffuseColor 1 0.7 0.3 specularColor 0.3 0 0 }
Sphere { radius 0.1 }
}
Separator {
# Middle block
Material { diffuseColor 0.6 0.6 1.0 } Cube { width 0.2 height 0.2 depth 0.2 }
}
Separator {
# Block
Transform { translation 0.3 0 0 }
Cube { width 0.15 height 0.2 depth 0.2 }
}
Separator {
# Block
Transform { translation -0.3 0 0 }
Cube { width 0.15 height 0.2 depth 0.2 }
}
}
FIGURE 292. VRML programming example
VSN |
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VSN see VOLUME SERIAL NUMBER.
VT-100 a computer terminal made by Digital Equipment Corporation that had a major impact on the computer industry in the early 1980s. It provided convenient control codes for positioning the cursor, clearing the screen, and selecting normal, bold, or underlined type. This makes it possible to implement full-screen, personal-computer-like software on an asynchronous terminal. Most implementations of Telnet can emulate the VT-100.
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WAP |
W
w00t see WOOT.
W3C see WORLD WIDE WEB CONSORTIUM.
w4rez see WAREZ.
WAI (Web Accessibility Initiative) part of the World Wide Web Consortium dedicated to increasing Web accessibility. Since 1999, it has published guidelines for web sites to help designers improve usability. In addition to helping users with physical disabilities, increasing the accessibility of a web site makes it easier to view the site on devices like phones.
wall transformer a small transformer, often including other power-supply components, that plugs into a wall outlet (Figure 293).
Wall transformers keep high-voltage AC completely outside the equipment being powered. Because of this, only the wall transformer, not the rest of the equipment, has to pass fire safety certifications. For this reason, they are very popular with manufacturers.
Most wall transformers are designed to burn out harmlessly when overloaded; there is no replaceable fuse. A dead wall transformer is a common cause of inoperative equipment.
It is very important not to substitute wall transformers unless you are sure that the replacement delivers the same voltage with the same polarity (arrangement of + and – connectors) and the same or greater maximum current (amperes, milliamperes). Equipment can be damaged by using the wrong power supply.
wall wart (slang) a WALL TRANSFORMER.
FIGURE 293. Wall transformer (“wall wart”)
wallpaper a picture or pattern displayed as a background in a windowed operating system.
WAN see WIDE-AREA NETWORK.
WAP
1.see WIRELESS ACCESS POINT.
2.(Wireless Application Protocol) an open global specification for wireless devices to interact with information providers. See www.wapforum.org.
war dialing |
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war dialing (slang) the practice of using an autodial modem to dial many telephone numbers in succession (e.g., 000-0000 to 999-9999) to see if a computer answers any of them. If so, attempts are made to break into the computer. If a human being answers, he or she hears a tone, or nothing at all. The practice was popularized by the movie Wargames (1983).
war driving (slang) the practice of driving or walking around town with a laptop computer, to see if it can connect to anyone’s wireless network.
Compare WAR DIALING.
warez pirated software, usually traded over the Internet on peer-to-peer networks. See PIRACY.
warm boot, warm start See BOOT.
warp to digitally manipulate an image so that it appears twisted or stretched (Figure 294).
FIGURE 294. Warp effect
watermark
1.a pattern visible when paper is held up to light; it is pressed into the paper during manufacturing. For example, U.S. government stationery has the Great Seal of the United States in its watermark.
2.a faint pattern or second image added to a digital image for identification or other purposes.
3.an invisible code placed in a digital image to identify it. See INVISIBLE
WATERMARK; STEGANOGRAPHY.
watt unit for measuring the rate at which electrical power energy is usually being consumed. One watt is equivalent to one joule per second. Wattage depends on both voltage and current, as follows:
Watts = volts × amperes
For example, a 5-volt, 10-ampere power supply delivers 50 watts. The amount of AC power going into the power supply is somewhat greater, depending on the inefficiency of the supply.
watt-hour the amount of energy consumed by using energy at the rate of one watt for one hour. One watt-hour equals 3,600 joules. In the United States, electricity costs about 10 cents for 1,000 watt-hours (one kilo- watt-hour).
.wav the filename extension for digitized sound wave files under Microsoft Windows.
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wave file a file containing a digital representation of sound waves. See
SAMPLING RATE; SOUND CARD; WAV.
wavetable synthesis a technique for synthesizing musical instrument sounds by computer using stored information about the waveforms produced by real instruments. Contrast
Wayback machine a service providing archived copies of many web pages from previous times. Because web pages often change, there would be a serious risk that much history would be lost if this archiving service did not exist. Web address: www.archive.org.
Web the WORLD WIDE WEB.
WEB a programming tool developed by D. E. Knuth to make it easier to create modular programs. WEB is a more abstract form of the Pascal (or, in later versions, C) programming language. The programmer is free to define procedures in any order and write blocks of code to be inserted into larger blocks written later. Heavy use of comments is encouraged and listings are printed elegantly with reserved words in boldface.
Web 2.0 a vague name for a number of new ways of using the WORLD WIDE WEB, especially those that involve SOCIAL NETWORKING and audience participation. “Web 2.0” is not the name of any specific technical standard.
web address a string of characters that identifies a file viewable on the
WORLD WIDE WEB, such as:
www.CovingtonInnovations.com/christian.html
It specifies a transfer protocol (usually http), the domain address of the site (such as www.CovingtonInnovations.com), and, optionally, a directory path and filename. On some systems, the directory is identified by the character ~ (tilde) and the account name of a user. See PROTOCOL;
URL.
web browser see BROWSER.
web log see BLOG.
web page a file of information made available for viewing on the WORLD and seen by the user as a page of information on the screen.
web page design the production of WEB PAGEs for others to view. Many web pages are badly designed. Here are some guidelines for designing a good one:
1.Decide on the purpose of your web page. What information do you want to communicate? What’s important and what’s not? Focus on conveying your message rather than showing off your repertoire of special effects.
2.Plan for maintainability. How soon will something have to be changed? Can frequently changed information be placed in separate files that are easier to update?
web page title |
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3.If you want people to visit your web site repeatedly, put something useful there, such as reference information, links to other sites, or free software.
4.Do not draw attention to the wrong things. The most important part of your message should be the most visually prominent. Unimportant graphics that blink or move can be very annoying.
5.Remember that you do not have a captive audience. People are not going to sit through time-consuming graphics or animations if what they really want could have been delivered more quickly.
6.Remember that some people still use older browsers. You probably don’t want to limit your audience to people who have this month’s version.
7.Use dark type on a white background for anything the reader may need to print out. Some browsers cannot print out light type on a dark background.
8.Attach links to informative words, not the word “here.” Instead of “Click here to learn about our new software,” just say “New software.”
See HTML.
FIGURE 295. Web page
web page title the descriptive text that appears in the browser’s title bar. The web page title is used as the name when the user creates a BOOKMARK.
web search the act of searching the WORLD WIDE WEB with a SEARCH ENGINE.
web server a computer that is attached to the Internet and contains web pages (HTML files) that can be viewed using a web browser. Every web page resides on a web server somewhere. The web server has to be connected to the Internet continuously, and it runs an HTTP server program
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such as Apache, Microsoft’s Internet Information Server, or Netscape’s Enterprise Server. The web server may also need to run special software (such as a CGI script) in response to a client’s request. See WEB PAGE;
WORLD WIDE WEB.
web services programs running on computers connected to the Internet that can interoperate with programs on other computers, using XML as a standard way of formatting data to be communicated. Standards for web services are being developed by OASIS. See also .NET FRAMEWORK.
web sight [sic] common spelling error for WEB SITE. A group of web pages is a site (location), not necessarily a sight (view).
web site a file or related group of files available on the WORLD WIDE WEB.
webcam A camera attached to a computer that distributes a live image to the WORLD WIDE WEB. Compare NETCAM. Physically, webcams and netcams are alike; the difference is in how they are used.
webcast (web broadcast) an event intended to be viewed simultaneously by numerous people connecting to the same web site. Webcasts often feature celebrity interviews, open-forum discussions, or product announcements. If too many people “tune in” at the same time, however, the server or network can be overloaded. Compare INTERNET RADIO; IPTV;
PODCASTING.
webinar a group of people viewing a seminar presented over the Web, sometimes with limited audience interaction.
webliography (web bibliography) a list of web-based documents on a specific subject.
webmaster the person who has principal responsibility for maintaining a site on the WORLD WIDE WEB and updating some or all of the WEB PAGEs.
weight the boldness (heaviness) of a style of type. For example, this is heavy-weight type and this is ordinary-weight type. Some fonts provide several different weights (light, medium, demibold, bold, and extra bold). See Figure 296.
FIGURE 296. Weight (of typefaces)
weld (in vector graphics) to join two or more objects so that the resulting single object has the outline of the group of objects.