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In the UNIX operating system, a background process that lies dormant waiting to perform some useful task. The sendmail daemon, for example, continually runs but becomes active only when E-Mail is sent or received. The FreeBSD Unix OS has it's own rendition.
This is an acronym for the online storage term, Direct Attached File System, an advanced methodology of a particular network data storage method.
This is an acronym for the X.500 network standard term, Directory Access Protocol. It is the foundation for all network directory services for Microsoft, Novell and the Internet. It has a smaller brother called LDAP.
1. In the current IT world, a dashboard is a user interface that, somewhat resembling an automobile's dashboard, organizes and presents information in a way that is easy to read. However, a computer dashboard is more likely to be interactive than the typical automobile dashboard. To a reasonable degree, most graphical user interfaces (GUI) resemble a dashboard. However, some product developers consciously employ this metaphor (and sometimes the term) so that the user instantly recognizes the similarity.
2. Some products that aim to integrate information from multiple components into a unified display refer to themselves as dashboards. For example, a product might obtain information from the local operating system in a computer, from one or more applications that may be running, and from one or more remote sites on the Web and present it as though it all came from the same source. Hewlett Packard developed the first such product, which began as a tool for customizing Windows desktops. Called Dashboard, the HP product was subsequently acquired by Borland and then a company called Starfish. Microsoft's Digital Dashboard tool incorporates Web-based informational elements (such as news, stock quotes, weather and the like) and corporate elements (such as E-Mail, applications, and similar) into Outlook. Dashboards may be customized in a multitude of ways and named accordingly, generally, for example as a general corporate or enterprise dashboard, or more specifically, as a CIO or CEO dashboard. As a rule, that type of display is a synopsis of more detailed units.
While data is usually information resulting from or produced by a program, it can be the programs themselves. Data can be in memory only or can be also stored on disk or some other media. The collection and (hopefully) effective use of data is why we do what we do.
Loosely, any aggregation of data; usually a large collection of data that has been formatted by some user-defined standard. Certain programs create and utilize the data in a database. Some common current examples are Access, Oracle, IFMX and SQL. Also see the abbreviation, DB.
data encryption key
A string of characters used to mathematically encode a message so that it can only be read by someone in possession of another related key.
Data Encryption Standard - DES
A popular, standard encryption scheme.
data link layer
Layer 2 of the OSI reference model. Provides reliable transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE divided this layer into two sublayers, the MAC sublayer and the LLC sublayer. Sometimes simply called link layer. Roughly corresponds to the data link control (DLC) layer of the SNA model. See also application layer, LLC, MAC, network layer, physical layer, PQ, presentation layer, session layer, and transport layer.
A piece of information sent between any online service and your modem, or from one networked computer to another. It is usually a predetermined size in a predetermined format, however, not always. See packet.
A term referring to the speed in bits of data being moved from one location to another. Generally, it refers to the speed of the flow of data measured in bits across a network, through an Internet connection, or from and I/O device such as a disk drive. You can see the conversion of flow rate units in our Data Rate Converter. If you are seeking byte conversion, please use our Memory and Storage Converter. For sample download times, try our Connection Speed - Download Speed Calculator.
A circuit board, smaller than a standard board or card, that attaches directly to the motherboard or another card. These usually provide an optional feature to the hosting card or board. See AMR.
The worldwide accepted abbreviation for decibel.
1. The worldwide accepted abbreviation for database.
2. The initial part of the designation for certain types of connectors; it was originally coined by the ANSI standards committee and is an abbreviation for data bus.
A designation for a particular type of connector. See our detailed explanation of serial communications. Also see the abbreviation, DB. You may also wish to see our detailed pin view of the connector.
A designation for a particular type of connector. See our detailed explanation of serial communications. Also see the abbreviation, DB. You may also wish to see our detailed pin view of the connector.
Direct Current. The type of electricity used in most computer internal circuits. See AC, power supply, volt and current.
Antiquated acronym for Direct Client-to-Client, a feature of some IRC client software, allowing users to communicate messages and files directly, bypassing a server. See peer-to-peer.
An acronym for Data Communications Equipment refers to serially connected communications devices, particularly modems. See also DTE.
A large mini-computer manufacturer in Germany in the 1970s and 1980s. They made a compatible computer to the Data General Nova and Eclipse series. They were taken over by Siemens. We did a lot of design work for them through 1984. Most of their market was in Europe, Africa and Asia.
An acronym for Double Data Rate, or SDRAM. It is touted to be the next generation of the current SDRAM. DDR finds its foundations on the same design core of SDRAM, yet adds advances to enhance its speed capabilities. As a result, DDR allows data to be read on both the rising and the falling edge of the clock, delivering twice the bandwidth of standard SDRAMS. DDR essentially doubles the memory speed from SDRAMs without increasing the clock frequency.
A slang term used by programmers. It generally means to troubleshoot a problem (a bug) in a program.
An acronym for Digital Equipment Corporation, commonly known as Digital, or most often, just DEC. They were an industry pioneer and now are a part of Compaq, which is now a part of HP. See them at HTTP://H18000.WWW1.HP.COM/.
1. A measurement of sound. Technically, a logarithmic measure of the ratio of two signal levels using the formula:
dB=20Log(V1/V2)=10Log(P1/P2), or just the simplified formula, dB=10Log(P1/P2).
2. Decibel is the unit used to express relative differences in signal strength. It is expressed as the base 10 logarithm of the ratio of the powers of two signals. Signal amplitude can also be expressed in dB. Since power is proportional to the square of a signal's amplitude (for example, a power ratio of 100 is equivalent to an amplitude ratio of 10), dB is expressed as follows:
dB = 20 log (A1/A2)
Logarithms are useful as the unit of measurement because
(a) signal power tends to span several orders of magnitude and
(b) signal attenuation losses and gains can be expressed in terms of subtraction and addition.
For example, suppose that a signal that passes through two channel segments is first attenuated in the ratio of 20 to 1 on the first leg and 7 to 1 on the second. The total signal degradation is in the ratio of 140 to 1. Expressed in dB, this becomes 13.01 (10 log 20) + 8.45 (10 log 7) = 21.46 dB. This reference chart helps to indicate the order of magnitude associated with dB.
1 dB attenuation indicates 0.79 of the input power survives
3 dB attenuation indicates 0.50 of the input power survives
10 dB attenuation indicates 0.1 of the input power survives
20 dB attenuation indicates 0.01 of the input power survives
30 dB attenuation indicates 0.001 of the input power survives
40 dB attenuation indicates 0.0001 of the input power survives
It should also be mentioned that often dB ratios are expressed using a third letter (or letters), such as dBm. The third letter is a reference level for the log operation. In our dBm example, dBm is used to define dB levels in a 50 Ohm RF system, using a 1 milliwatt reference level. We have several calculators that deal with decibels on our electronics Electronics Calculators, Converters and Tables page.
Refers to numbers in base 10 (the numbers we use in everyday life). For example, the following are decimal numbers: 9; 100345000; -256 and 3,567, even though none contain a decimal. Note that a decimal number is not necessarily a number with a decimal point in it. Numbers with decimal points (that is, numbers with a fractional part) are called fixed-point or floating-point numbers. In addition to the decimal format, computer data is often represented in binary (base 2), octal (base 8), and hexadecimal (base 16) formats. The decimal is often called "dot" in computer jargon. See DOTCOM. For a demonstration of decimal number conversion, try our Base 2/10/16 number converter.
In navigation, often the combination of degrees, minutes and seconds are expressed as degrees, with a decimal fraction that indicates the number of minutes and seconds, all in one number. The formula for conversion is:
There are 60 seconds in 1 minute and 60 minutes in 1 degree. So, for an example of converting:
55:45:36 North latitude converts to
(65 degrees + 45 minutes * (1 degree/60 minutes) + 36 seconds * (1 minute/60 seconds) * (1 degree/60 minutes) = 55.76 decimal degrees latitude. Longitude decimal degrees are done in the same manner.
A tool to convert executable program code (sometimes called object code) such as an .EXE or .COM file, into some form of higher level programming language so that it can be read by a human. Decompilation is a type of reverse engineering that does the opposite of what a compiler does. There are many possible reasons for decompilation or disassembly, (not all of them good) such as understanding a program flow, recovering the source code for purposes of archiving or updating, finding viruses, debugging programs, and translating obsolete code. Decompilation was first used in the 1960s to facilitate the migration of a program from one platform to another. Decompilation is not always successful for a number of reasons. It is not possible to decompile all programs, and data and code are difficult to separate, because both are represented similarly in most current computer systems. The meaningful names that programmers give variables and functions (to make them more easily identifiable) are not usually stored in an executable file, so they are not usually recovered in decompiling. Decompilation is sometimes used unethically, to reproduce source code for reuse or adaptation without permission of the copyright holder. Programs can be designed to be resistant to decompilation through protective means such as obfuscation. The recompile after a decompile does not always generate the same object code.
A mathematical process in which a number, most often one, is subtracted from another number. This process is often used in programming. See increment.
1. A telephone line that is reserved for the singular purpose of providing a data connection between two computers, systems or networks.
2. An isolated power connection that only a computer feeds from.
3. A particular conversation that has worked well in singles' bars over the years.
A value, condition or modifiable choice selection that is selected unless otherwise changed.
The filename that you use for the primary document for directories within your site. Some examples include the following: index.htm, index.html, default.htm, default.asp. This is the first page of a website and the one that is loaded if no other document is specified.
The angular degree (abbreviated with deg or º) is a unit of plane angular measure used in many engineering applications, by aviators, navigators and by most lay people. There are 360 angular degrees in a complete circle. Thus, one angular degree is equivalent to approximately 0.00277778 of a circle. See decimal degree.
Delete and Reinstall
As a last resort, it is sometimes necessary to delete a piece of software and reinstall it in order to fix a problem. This is in contrast to just reinstalling it. In the case of major Windows problems, Microsoft techs often use the words that set fear into the hearts of most, format and reinstall.
Removing something from your computer. It could be text from a word processing window, or a file from your hard disk drive. Deleting programs or suites of programs is difficult in that the usually have data in multiple directories and information that has been installed into the INI files and/or registry. Though it is often necessary to free space on your hard disk, it is a process that frequently causes trouble or a complete shut down of your computer. After working on these computers for a bit (no pun intended) too long, you often feel you hit the delete key to your brain.
An optional E-Mail feature that notifies you when your E-Mail message has been delivered to its recipient. See also Read Receipts.
A common three-phase connection shaped schematically like the Greek Delta. The end of one phase is connected to the beginning of the next phase, or vice versa.
A three-phase electrical transformer with has ends of each of three windings electrically connected.
To come out of online lurking mode; to actively participate in a online discussion after a period of just watching or lurking. This term is derived from episodes of Star Trek that feature Klingon warships that can hide ("cloak") or appear ("decloak") at will.
Conversion of a carrier signal or waveform (analog) into an electrical signal (digital). It is the second of two processes that a modem accomplishes. See modulate.
See Data Encryption Standard and data.
Generic name for a part, in this case, usually a part of a computer. The part can be a disk drive, a controller or perhaps a modem. All the components are devices. In certain environments, such as Windows, the devices are controlled or monitored by the device manager.
The monitoring and control function of computer parts making up the computer. Device Manager is an OS feature that lets you view and change the properties of all devices attached to your computer. To get to the device manager in Windows, right click on the My Computer icon, choose properties, then click on the device manager tab. You may also get there by clicking on the System icon inside the Control Panel. From there you can select a variety of management options. The device manager is found in both Windows 95, 98, ME, 2000, XP and Macintosh PC platforms. Windows 2000 contains an improved device manager that detects plug-and-play hardware and displays a large list of supported hardware. XP has carried that a step further.
The abbreviation for Digital Flash Media, a generalization for all type of digital media devices such as but not limited to CF (CompactFlash), Memory Stick (MS), MultiMediaCard (MMC), Secure Digital (SD), SmartMedia (SM), USB Flash Drive (USBFD) and x D Picture Card (x D). The sizing for the media is often confusing as in contrast to disk and memory size designation comparison, most drive manufacturers designate a MB as 1,048,576 (2 to the 20th power) bytes, while most DFM manufacturers designate it as 1,000KB bytes. See TANS.
Dynamic Host Configuration Protocol (DHCP) is a network configuration that allows Internet maintenance and setup to be performed from a central site rather than by end users, among other activities. It lets network administrators centrally manage and automate the assignment of Internet Protocol (IP) addresses in an organization's network. Using the Internet Protocol, each machine that can connect to the Internet needs a unique IP address for identification, which is assigned when an Internet connection is created for a specific computer. Without DHCP, the IP address must be entered manually at each computer in an organization and a new IP address must be entered each time a computer moves to a new location on the network; this is called Static assigment. DHCP lets a network administrator supervise and distribute IP addresses from a central point and automatically sends a new IP address when a computer is plugged into a different place in the network. DHCP uses the concept of a "lease" or amount of time that a given IP address will be valid for a computer. The lease time can vary depending on how long a user is likely to require the Internet connection at a particular location. It's especially useful in education and other environments where users change frequently. Using very short leases, DHCP can dynamically reconfigure networks in which there are more computers than there are available IP addresses. The protocol also supports static addresses for computers that need a permanent IP address, such as Web servers. DHCP is an updated extension of an earlier network IP management protocol, Bootstrap Protocol (BOOTP). DHCP is a more advanced protocol, but both configuration management protocols are commonly used and DHCP can handle BOOTP client requests. Some organizations use both protocols, but understanding how and when to use them in the same organization is important. Some operating systems come with DHCP servers. A DHCP or BOOTP client is a program that is located in (and perhaps downloaded to) each computer so that it can be configured. Most often the DHCP process is handled by the ISP or by a router, or both.
An acronym for Dynamic HyperText Markup Language. Though the final definition of DHTML has not yet been made, Microsoft has decided to implement its own version in IE 5.5 and subsequent browsers.
1. Refers to Web content that changes each time it is viewed. For example, the same URL could result in a different page depending on any number of parameters, such as:
Geographic location of the reader
Time of day
Previous pages viewed by the reader
Profile of the reader
2. Dynamic HTML refers to new HTML extensions that will enable a Web page to react to user input without sending requests to the Web server. Microsoft and Netscape have submitted competing Dynamic HTML proposals to W3C, which is producing the final specification. Microsot decided not to wait and adopted its own version. The first proposal was made in late 1997.
1. A dialer is either internal to or external from your browser or ISP supplied software. It handles all of the normal telephone connection operations. Those dialing functions can be for voice connections also.
2. A problem program that connects you to some location for some reason that may not be known to you. There are dialers that dial networks just to create charges on your phone bill.
1. A temporary connection between computers established over a telephone line.
2. To establish a temporary connection to another computer.
3. The process of initiating a switched connection through the network; when used as an adjective, this is a type of communication that is established by a switched-circuit connection.
4. A type of phone line that is used for voice connections. The opposite would be some kind of full time connection like DSL.
1. A telephony acronym for Direct Inward Dialing is a feature allowing callers to directly reach a PABX extension without an operators assistance.
2. An acronym for Digital IDentification (ID), which is a digital signature.
3. A slang acronym for DOS Is Dead!
A dielectric material is one that is a poor conductor of electricity, but an efficient supporter of electrostatic fields. If the flow of current between opposite electric charge poles is kept to a minimum while the electrostatic lines of flux are not impeded or interrupted, an electrostatic field can store energy. This property is useful in capacitors, especially at radio frequencies. Dielectric materials are also used in the construction of radio frequency transmission lines.
In practice, most dielectric materials are solid. Examples include porcelain (ceramic), mica, glass, plastics, and the oxides of various metals. (See our dielectric lookup table with some examples.) Some liquids and gases can serve as good dielectric materials. Dry air is an excellent dielectric, and is used in variable capacitors and some types of transmission lines. Distilled water is a fair dielectric. A vacuum is an exceptionally efficient dielectric.
An important property of a dielectric is its ability to support an electrostatic field while dissipating minimal energy in the form of heat. The lower the dielectric loss (the proportion of energy lost as heat), the more effective is a dielectric material. Another consideration is the dielectric constant, the extent to which a substance concentrates the electrostatic lines of flux. Substances with a low dielectric constant include a perfect vacuum, dry air, and most pure, dry gases such as helium and nitrogen. Materials with moderate dielectric constants include ceramics, distilled water, paper, mica, polyethylene, and glass. Metal oxides, in general, have high dielectric constants.
The prime asset of high dielectric constant substances, such as aluminum oxide, is the fact that they make possible the manufacture of high value capacitors with small physical volume. But these materials are generally not able to withstand electrostatic fields as intense as low dielectric constant substances such as air. If the voltage across a dielectric material becomes too great, for example, if the electrostatic field becomes too intense, the material will suddenly begin to conduct current. This phenomenon is called dielectric breakdown. In components that use gases or liquids as the dielectric medium, this condition reverses itself if the voltage decreases below the critical point. But in components containing solid dielectrics, dielectric breakdown usually results in permanent damage.
A particular type of operational amplifier where the output voltage is in proportion to the difference between the inputs.
Unlike the comparator, which can based on exactly the same IC, the Op-Amp has two individual inputs instead of one input and one reference value. This use is sometimes called a proportional amplifier or subtractor.
The digital elite. Derived from "literati".
1. Describes any system based on discontinuous data or events. Computers are digital machines because at their most basic level they can distinguish between just two values, 0 and 1, or off and on. There is no simple way to represent all the values in between, such as 0.25. All data that a computer processes must be encoded digitally, as a series of zeroes and ones. The opposite of digital is analog. A typical analog device is a clock in which the hands move continuously around the face. Such a clock is capable of indicating every possible time of day. In contrast, a digital clock is capable of representing only a finite number of times (every tenth of a second, for example). In general, humans experience the world analogically. Vision, for example, is an analog experience because we perceive infinitely smooth gradations of shapes and colors. Most analog events, however, can be simulated digitally. Photographs in newspapers, for instance, consist of an array of dots that are either black or white. From afar, the viewer does not see the dots (the digital form), but only lines and shading, which appear to be continuous. Although digital representations are approximations of analog events, they are useful because they are relatively easy to store and manipulate electronically. The trick is in converting from analog to digital, and back again. This is the principle behind compact discs (CDs). The music itself exists in an analog form, as waves in the air, but these sounds are then translated into a digital form that is encoded onto the disk. When you play a compact disc, the CD player reads the digital data, translates it back into its original analog form, and sends it to the amplifier and eventually the speakers. Internally, computers are digital because they consist of discrete units called bits that are either on or off. But by combining many bits in complex ways, computers simulate analog events. In one sense, this is what computer science is all about.
2. The street name often given to Digital Equipment Corporation, DEC or Digital, now owned by Compaq, now owned by HP. See them at HTTP://WWW.COMPAQ.COM.
A localized area of many ISPs' services that provides local information and shopping. Most major cities in the US will have a Digital City area on most of the ISP services.
An effort by some school systems to give a select group of high school students a detailed start into the IT world. Courses are selected to give both hardware and software training directed at the function side, rather than the user side of computers.
A signal that varies only at regular time intervals and has one or two or more predetermined amplitudes for each interval. See DSP.
The process of transformation of another media to one of digital information. A scanner digitizes images; a video digitizer converts analog video (your old VHS cassette) into digital video. There are numerous ways to digitize sound. If you use a digitizer tablet, you draw an image on the tablet with a pen. The tablet converts via the appropriate software, the drawing into a digital image on your computer. Most people feel that it is much easier than trying to draw with your mouse.
A tablet to allow data input from an X-Y co-ordinate positioning of a mouse like device to a CAD/CAM program.
1. This is a type of memory, an acronym for Dual Inline Memory Module; it is hardware inside the computer. It comes in various sizes and configurations to suit the needs of the system and user. It is the design architecture technology for most 233mhz and faster Pentium class machines. DIMMs are small memory cards with data buses of 64, 72, or 80 bits. Unlike SIMMs, DIMMS have functionally unique contacts on the front and back of the card. They are designed to meet JEDEC standards so that machine interchangability problems cease. They can be buffered or unbuffered depending on the particular design. DIMMs come with a variety of sizes, speeds, and features. DIMMS are in the 72, 144 and 168 pin configuration packages and come in different capacities based on architecture:
Fast Page Mode (FPM)
Extended Data Out(EDO)
Synchronous DRAM (SDRAM)
in different bus speeds of:
66Mhz 16, 32, 64, 128 and 256 MB modules
100MHZ 16, 32, 64, 128, 256, 512MB and 1GB modules
133Mhz only comes in 64, 128 and 256MB modules at the time of this writing.
2. A printed circuit board with gold or tin/lead contacts and memory devices. A DIMM is similar to a SIMM, but with this primary difference: unlike the metal leads on either side of a SIMM, which are "tied together" electrically, the leads on either side of a DIMM are electrically independent.
The designation given to a European design connecting plug; it is an acronym for Deutsche Industrinorm; the rough German equivalent of our EIA. The DIN plug is round with an indented key to allow a connection to plug in only one way. The number of pins in the connector varies. For instance, a five pin DIN (DIN5) was the connector used for PC keyboards for many years. The DIN8 is a type of serial connector.
The diode is an electronic component that allows the passage of current in only one direction. They are solid state semiconductor devices and typically need more than
0.6 volts to operate. In a normal diode, current flows from the positive anode to the negative cathode. Early diodes were in reality, vacuum-tube rectifiers, consisting of an evacuated glass or steel envelope containing two electrodes—a cathode and an anode. Because electrons can flow in only one direction, from cathode to anode, the vacuum-tube diode could be used as a rectifier. That is still a use of diodes in today's electronic circuits; now they are all semiconductor diodes. The simplest of these, the germanium point-contact diode, dates from the early days of radio, when the received radio signal was detected by means of a germanium crystal and a fine, pointed wire that rested on it. In modern germanium (or silicon) point-contact diodes, the wire and a tiny crystal plate are mounted inside a small glass tube and connected to two wires that are fused into the ends of the tube. Junction-type diodes consist of a junction of two different kinds of semiconductor material. There are literally thousands of different specification diodes. They are usually identified with a number but some are color coded. You can use our Diode Color ID Band Table to identify such diodes.
The Zener diode is a special junction-type diode, using silicon, in which the voltage across the junction is independent of the current through the junction. Because of this characteristic, Zener diodes are used as voltage regulators. (Try our Zener Diode Calculator.) Another special junction-type diode is used in solar cells; a voltage appears spontaneously when the junction is illuminated. In light-emitting diodes, commonly called LEDs, the exact opposite happens. A voltage applied to the semiconductor junction results in the emission of light energy. LEDs are used in numerical displays such as those on electronic digital watches and pocket calculators. They are usually in one of two shapes, bars or dots, and come in various sizes. Bars are placed in a particular pattern to form letters or numbers; when the are letters, they are called an alpha display. When the are numbers, they are called a numeric display. In may cases, they can be either and are known as an alpha-numeric display.
Dual Inline Package; a form of DRAM component packaging. DIPs can be installed either in sockets or permanently soldered into holes extending into the surface of the printed circuit board. The DIP package was extremely popular when it was common for memory to be installed directly on a computer's motherboard.
A series of tiny switches built into circuit boards. The housing for the switches, which has the same shape as a chip, is the DIP. An acronym for Dual Inline Package, DIP switches enable you to configure a circuit board for a particular type of computer or application. The installation instructions should tell you how to set the switches. DIP switches are always toggle switches, which means they have two possible positions, on or off. (Instead of on and off, you may see the numbers 1 and 0. See binary.) One of the historic advantages of the Macintosh over the PC was that it allowed you to configure circuit boards by entering software commands instead of setting DIP switches. However, the new Plug & Play (often called Plug & Pray) standard developed by Microsoft makes DIP switches obsolete for PC expansion cards too. See contact. You may wish to consult with your local GURU and your Pastor before attempting to use these.
1. An index of the files on a disk. A directory can contain individual files in addition to other directories. Also commonly known as a folder. It is the Unix equivalent of a 'folder' on a Mac, all files are stored in directories. A directory can be created with the mkdir (MD) command and empty directories are removed with rmdir (RD); directories can be changed with the chdir (CD) instruction.
2. A site, similar in operation to a search engine and often called a search engine or search site, that has a human created and edited listing of other sites, usually grouped by category of sites with similar objectives or interests. Though they certainly have a place on the Internet in the world of niche sites and those that avoid pornography, they are fast going by the wayside except for specialties and except for those that have developed into portals and vortals. Those search facilities that use robots can gather more information in a shorter amount of time, with less human intervention.
Directory of Services
An ISP's list of areas online. This list is vast and updated often. You can usually search the directory of services, on most online services, by going to a localized search device known as Keyword.
A tool that translates object code into native assembler language. There are a number of different reasons for decompilation or disassembly, such as understanding a program flow, recovering the source code for purposes of archiving or updating, finding viruses, debugging programs, and translating obsolete code. Neither method is as efficient as having the original source code since comments are not assembled or compiled, making reading of the resulting disassembled or decompiled code much more difficult.
A round plate or platter on which data can be encoded. Though the correct spelling is disk, it is often seen as disc. There are two basic types of disks, magnetic disks and optical disks. On magnetic disks, data is encoded as microscopic magnetized needles on the disk's surface. You can record and erase data on a magnetic disk any number of times, just as you can with a cassette tape. Magnetic disks come in a number of different forms:
1. floppy diskette: A typical 5¼-inch PC floppy diskette can hold 360K or 1.2MB. 3½-inch floppies normally store 720KB, 1.2MB or 1.44MB of data.
2. hard disk: Hard disks (one kind of disk drive) can store anywhere from 20MB (or less, depending on which old box you found it in) to more than 500GB. Hard Disks are also from 10 to 1000 times faster than floppy disks.
3. removable cartridge: Removable cartridges are hard disks encased in a metal or plastic cartridge, so you can remove them just like a floppy disk. Removable cartridges are very fast, though usually not as fast as fixed hard disks. They are convenient for moving large quantities of data from one computer to another.
Optical disks (also a disk drive) record data by burning microscopic holes in the surface of the disk with a laser. To read the disk, another laser beam shines on the disk and detects the holes by changes in the reflection pattern. Optical disks come in three basic forms:
1. CD-ROM: Most optical disks are read-only. When you purchase them, they are already filled with data. You can read the data from a CD-ROM, but you cannot modify, delete, or write new data. The data reader is also called a CD-ROM but is usually called a drive or CD drive for clarity.
2. WORM: Stands for write-once, read-many. WORM disks can be written on once and then read any number of times; however, you need a special WORM disk drive to write data onto a WORM disk. You can USUALLY read WORMs from a normal CD drive.
3. erasable optical (EO): EO disks can be read to, written to, and erased just like magnetic disks. The reader and writer are both called optical drives.
The machine that spins a disk is called a disk drive. Within each disk drive is one or more heads (often called read/write heads) that actually read and write data. Accessing data from a disk is not as fast as accessing data from main memory, but disks are much cheaper. And unlike RAM, disks hold on to data even when the computer is turned off. Consequently, disks are the storage medium of choice for most types of data. Another storage medium is magnetic tape. But tapes are used only for backup and archiving because they are sequential-access devices (to access data in the middle of a tape, the tape drive must pass through all the preceding data). A new disk, called a blank disk, has no data on it. Before you can store data on a blank disk, however, you must format it.
The actual physical hard disk or floppy disk drive, as opposed to the removable media. The media is called a diskette or removable disk. See floppy drive.
A form of removable media. See disk and disk drive. See floppy diskette.
Different patterns of ringing that allow a user to identify the source of the call, outside, or inside (intercom) or who the call is for. Usually two burst or three burst with different durations. Also known as ringmate, custom ring, identifying ring master.
An acronym for DIgital Video Express, a new DVD (DVD-ROM) format being promoted by several large Hollywood companies, including Disney, Dreamworks SKG, Paramount and Universal. The idea was financed mainly by retail electronics giant Circuit City. The idea was finally scrapped in the third quarter of 1999 as being too difficult to put into operation and because of lack of retail interest. With DIVX, a movie (or other data) loaded onto a DVD-ROM could be playable only during a specific time frame, typically two days. As soon as you began playing a DIVX disc, the counter starts. Each DIVX player had to be connected to a telephone outlet to communicate with a central server to exchange billing information. This was a retail and lease program. DIVX discs had the potential to ultimately replace video tapes. They were especially convenient for video rentals because there were no late fees. Once you purchased a DIVX title, you never needed to return it. However, DIVX threw a fatal (to itself) monkey wrench in the DVD market because the DIVX format was not backward compatible with other peer DVD-ROM players. This meant that you needed to buy a new DIVX player to play DIVX titles. Understandably, people and companies who have already invested in non-DIVX players were not pleased. It's not nice to tick off the yuppies! Though down for the moment, I am quite certain this or a similar "disposable" DVD will appear in the future. See our DIVX Bitrate Calculator.
1. Acronym for Data Link Control, the second lowest layer in the OSI Reference Model. Every network interface card (NIC) has a DLC address or DLC identifier (DLCI) that uniquely identifies the node on the network. Some network protocols, such as Ethernet and Token-Ring use the DLC addresses exclusively. Other protocols, such as TCP/IP, use a logical address at the Network Layer to identify nodes. Ultimately, however, all network addresses must be translated to DLC addresses.
2. In TCP/IP networks, this translation is performed with the Address Resolution Protocol (ARP). For networks that conform to the IEEE 802 standards (e.g., Ethernet ), the DLC address is usually called the Media Access Control (MAC) address.
1. An acronym for Dynamic Link Library. A file (library) of executable functions or data that is used by a Windows application or by Windows itself. By design, a DLL provides one or more distinctive functions; a program accesses the functions by creating either a static or dynamic link to the DLL and to subsequent functions or data within. A static link remains constant during program execution while a dynamic (on the fly) link is created by the program as needed. DLLs can also contain only data or a combination of both functions and data. DLL files usually end with the extension .dll, however can be .exe, drv, or .fon. A DLL can be used by several applications at the same time. Some DLLs are provided with the Windows operating system and available for any Windows application; hence results and stability are always predictable. Many DLLs are written for a particular application and are loaded with the application. In infrequent situations, DLLs have the same name and are the cause of system crashes as one overwrites another and causes totally unexpected results.
2. A file extension for a DLL file; see .DLL.
An acronym for Digital Light Processing, a trademark and creation of Texas Instruments design. DLP is a technology display solution for projectors and projection TV. The technology uses an optical semiconductor to recreate source material with a fidelity analog systems cannot match. It is an opposing technology to LCD functions, yet works quite differently than LCD. Instead of having glass panels through which light is passed, the DLP chip is a reflective surface made up of thousands of tiny mirrors with each mirror representing a single pixel. In a typical DLP projector, light from the projector's lamp is directed onto the surface of the DLP chip. The mirrors move upon command, back and forth, directing light either into the lens path to turn the pixel on, or away from the lens path to turn it off. The more expensive units have three DLP units, one for each processed color channel, red, green or blue.
An acronym for Direct Memory Access. This is a particular method of getting information from memory, usually large blocks of memory by addressing it directly rather than through normal buffers and normal protocol. The calling software (sometimes embedded in hardware) must be intelligent enough where to find that particular block of memory. This is a method usually used by fast disk controllers, tape controllers, SCSI controllers and intelligent database operations. It is often 20 times faster than conventional methods of access.
An acronym for Discrete Multi-Tone modulation. It is an ADSL modulation technique that splits bandwidth usage usage into sub-channels for maximum data transfer. A channel is then optimized for modulation if certain channels cannot transmit data. Specifically, there are 256 sub-channels in an ADSL DMT modulation, 32 of which are reserved for upstream data. DMT is the most widely endorsed industry standard for ADSL.
The base level stuff that made OJ's trial a farce. Computers don't have it...YET!
1. A behind-the-scenes Internet service which translates Internet domain names (such as aol.com) to their corresponding IP addresses (such as 126.96.36.199), and vice versa, allowing Internet users to use familiar names rather than IP addresses. See Domain Name System. The equivalent in a city might be your street address and the local land plot formal name kept by the city or county. Copies of the Domain Name System are distributed through the Internet.
AOL can be accessed through HTTP://WWW.AOL.COM.
2. A local (LAN) or Intranet database system which looks up host IP addresses based upon domain names. For example if you ask for "mysystem.lan" it will return "188.8.131.52".
3. It is the mechanism by which human-readable hierarchal names are translated to IP addresses, and vice-versa.
This design standard was developed by CableLabs and approved by the ITU in March 1998. It is an acronym for Data Over Cable Service Interface Specification and it defines interface standards for cable modems and supporting equipment. With certification from CableLabs, manufacturers will be able to produce cable modems for retail, so consumers no longer have to depend on leased cable modems from their cable providers. Other devices that recognize and support the DOCSIS standard include HDTVs and Web enabled set-top boxes for regular televisions. DOCSIS specifies very respectable downstream traffic transfer rates between 27 and 36 Mbps over a radio frequency (RF) path in the 50 MHz to 750+ MHz range, and upstream traffic transfer rates between 320 Kbps and 10 Mbps over a RF path between 5 and 42 MHz. But, because data over cable travels on a shared loop, individuals will see good transfer rates degrade as more users gain access. In 1998, there were 1.2 million cable modems installed across the United States with an average price of $245 per unit, and by 2004, research reports predict there will be 24.3 million units installed across the US with an average price of $50 per unit.
A term given usually to the operating instructions for a program, system or hardware apparatus. It is often used to describe the text backup of a programmer's efforts in writing a program. It usually contains a flow chart and list of variables and what they do as a very minimum.
See Dolby Digital.
A particular sound format originally associated with noise reduction and hiss elimination. It was originally used on cassette tapes to make them clearer. It is now associated with multimedia and Home Theater in regards to sound. A standard for high-quality digital audio that is used for the sound portion of video stored in digital format, especially videos stored on DVD-ROMs, often termed just DVD. Dolby Digital delivers 6 channels in the so called "5:1" configuration: left, right, and center screen channels, separate left and right sounds, and a subwoofer channel. This is sometimes called surround sound or 3D sound. See audio and AC-3.
Acronym for Document Object Model, the specification for how objects in a Web page including text, graphic images, headers and layout instructions, various type of links, and other markup instructions, are represented. The DOM defines what attributes are associated with each object, and how the objects and attributes can be manipulated. Dynamic HTML (DHTML) relies on the DOM to dynamically change the appearance of Web pages after they have been downloaded to a user's browser. Unfortunately, in this and everything else that would yield conformity, the two leading browsers, Netscape Navigator and Microsoft Internet Explorer (IE), use different DOMs. This is one reason why their respective implementations of DHTML are so different. Both companies have submitted their DOMs to the World Wide Web Consortium (W3C) for standardization, which now has the daunting task of specifying a standard DOM without alienating either of the browser giants. The W3C's DOM specification will support both HTML and XML.
An Internet domain is a subsection of the Internet. The primary domains of the Internet are .COM, .NET, .MIL, and .ORG, which refer to Commercial, Network, Military, and Organization (originally non-profit but no longer). These domains are administered by the InterNIC. Each domain has a primary and secondary Domain Name Server associated with it. DNS.
Prejudice against people on the basis of their Internet address (what domain they are from). For example, adopting a dismissive (see "get out of town"...) attitude towards anyone who posts from a commercial online service. "Why should anyone listen to you, you're posting from aol.com"!
The official name of a computer connected to the Internet. Domain names are derived from a hierarchical system, with a host name followed by a top-level domain category. The top-level domain categories (for the U.S.) are .com (for commercial enterprises), .org (for non-profit organizations), .net (for network services providers), .mil (for the military), and .gov (for government). Some Internet domain names include the computer server name, other sub-domains, and/or country abbreviations (e.g., us). Domain names act as easy-to-remember addresses for product or company information. As such, they are often subject to disputes between competing commercial interests. Most domain names are assigned by the InterNIC. You can find out more about InterNIC at HTTP://WWW.INTERNIC.NET.
DNS (Domain Name Server)
A computer that translates domain names (aol.com, gnn.com) into IP addresses (184.108.40.206). Web browsers, Internet mail and all other forms of Internet communications use a DNS (both the server and the service) to route information.
Domain Name System - DNS
The pigtail attachment to a PCMCIA (PC Card) that allows connection to an outside service, such as a network, direct connection to another computer or to a telephone service. The connector can be for a coax, RJ-11, RJ-45 or other similar device.
The acronym given to the term Disk Operating System. While it can mean ANY disk OS, it usually refers to Microsoft's DOS for IBM compatibles. The same term refers to ALL the releases through the last released version DOS 6.22; there is a DOS like platform under Windows 95 and 98 (not NT or W2000) but Microsoft is quick to say it is not DOS, though it does run some DOS software. Support and Microsoft DOS information can be accessed through HTTP://WWW.MICROSOFT.COM.
The acronym given to the term for an attack specifically designed to prevent the normal functioning of a system and thereby to prevent lawful access to the system by authorized users. Hackers can cause denial of service attacks by destroying or modifying data or by overloading the system's servers until service to authorized users is delayed or prevented.
The slang name given to the group of companies doing business on the Internet. Usually, they have gone public in an offering of some sort. The name is derived from the .COM on the end of the domain name. See dot.
The descriptive term in monitors and televisions that is often described as the amount of space between each pixel, though correctly, it is actually the spacing between same color red, green, or blue phosphor dots on the screen. Some manufacturers specify aperture grille spacing instead of dot pitch. The smaller the dot pitch, the sharper the image.
To transfer data from a larger "host" system to a smaller "client" system's hard drive or other local storage device. See also upload, downstream and upstream.
Monetary charges associated with downloading a file from a commercial online service. This method of information exchange is not very popular.
The download count in a file description indicates how many times that file has been downloaded. This can be an indicator of the file's popularity. This sort of record is kept by the download servicer's host computer and software.
An ISP tool that keeps track of your downloaded files. Download Manager is offered by some online services to help less experienced users keep track of resources. It can usually be accessed from the FILE menu, if offered.
Transferring files from a host computer, such as AOL, MSN or CIS, to your personal computer. It's very similar to copying files from your hard disk drive to a floppy disk.
The communications flow from the network towards the customer premises. Upstream is the opposite direction.
An acronym for Digital Pulse Wireless; also known as Ultra Wideband Radio. It is the revolutionary wireless technology for transmitting large amounts of digital data over a wide electromagnetic radiation spectrum of frequency bands with very low power. DPW not only can carry a huge amount of data over a short distance (up to 250 feet) at very low power (less than 0.5 milliwatts), but has the ability to be less ine of sight oriented, that is, it can in most cases carry signals through doors and other obstacles that tend to reflect signals at more limited bandwidths and a higher power.
1. To move an image or a window from one place on the screen to another by grabbing it with a mouse or other pointing device and pulling it to a new location.
2. A job you don't like doing, like doing paper work.
1. An acronym for Dynamic Random Access Memory. It is the most common form of system memory packaging. DRAM can hold a charge (that is, data) for only a short period of time. Dynamic means the DRAMs need a constant refresh (pulse of current through all of the memory cells) to keep the stored information. Therefore, to retain the data it must be refreshed periodically. If the cell is not refreshed, the data is lost.
2. DRAM is the most common type of memory and is "dynamic" because in order for the memory chip to retain data, it must be refreshed constantly (every few milliseconds). DRAM temporarily stores data in a cell composed of a capacitor and a transistor. Each cell contains a specified number of bits. These cells are accessed by row addresses and column addresses.
The generic name for any physical hard disk drive, floppy disk drive, optical disk drive, DVD drive or tape drive. This is the device and not the removable media.
1. Low-level software that provides an interface between Operating System and the hardware devices. A driver exists to allow for device-independent applications. From time to time, drivers must be replaced whenever a new or updated application is installed.
2. A mechanism of planned hardware replacement, or so say some computer experts, where new operating systems are released without device driver support for older hardware. In many cases, as operating systems change, technology has changed so much that even though devices still work, they are no longer used and hence, are no longer supported. As an example, when was the last time you used an 8 inch floppy disk?
3. In hardware, a circuit that provides input to another circuit. It is usually termed a preamplifier, or preamp.
4. The big gun in your golf bag.
5. Often, a loose nut behind the wheel.
drop down box
A window that only exists while you click on it. Menus at the top of every screen are examples of drop down boxes.
A server user service action that allows Domain Name System (DNS) and similar services to be utilized by a particular group of computers.
An acronym for Digital Subscriber Line. A method of connecting full time to the Internet at speeds approaching and sometimes beyond T1 but without the full bandwidth. In most locations, the cost is a small fraction of the cost of T1 or T3. The service runs on one pair and sometimes two pair wires and allows voice on the same line. Digital Subscriber Line service is a high-speed data service that works over copper telephone lines and is typically offered by telephone companies. The real beauty of DSL technology is that it works on existing POTS lines (Plain Old Telephone Service) which allows the phone companies to provide this service without costly installation of higher-grade cable. DSL uses a different part of the frequency spectrum then analog voice signals, so it can work in conjunction with your standard analog POTS service, sharing the same pair of wires. This may seem counter-intuitive, but that is one of the real strengths of this technology. It can piggy-back right on top of your existing phone line, without even disturbing that service. You can even use your analog portion of the phone line as a modem or FAX line, while simultaneously using the data portion for your DSL access. Not surprisingly, there's a slew of terms and acronyms that get used when discussing DSL technology. Starting at the beginning, DSL refers to a digital subscriber line that a telephone company central office (CO) provides to an end user. There are a host of versions and flavors of DSL, which has led to the common designation of "xDSL" when referring to this type of technology in general. The most common service, and the one you'll be looking at if you're considering home DSL Internet access, is ADSL, for Asymmetric Digital Subscriber Line. Being the most common form, the "A" is often dropped, and when someone is just talking DSL, it's probably ADSL. ADSL can support downstream bandwidths of up to 8 Mbps and upstream bandwidths of 1.5 Mbps. For comparison, a T1 connection also provides 1.5 Mbps. An important variation of ADSL is called G.Lite, DSL-Lite, or UADSL (Universal ADSL), and is a notched-down version aimed at the immediate consumer market. Going by many names, this service provides speeds up to 1.5 Mbps downstream and 384 kbps upstream. Another similar offering is CDSL (Consumer DSL), which is a smaller-bandwidth Rockwell variation. Some of the other variations include HDSL (High-bit-rate DSL), SDSL (Symmetric DSL) and VDSL (Very-high-bit-rate DSL). HDSL was the original form of DSL technology, developed in the early 90's, as an improved way to provide T1/E1 (1.5/2.0 Mbps) services by the telephone companies. It uses 4 copper wires (2 pairs) and offers a wider coverage area than previous methods. SDSL, also sometimes called HDSL-2, is an enhanced version of HDSL that allows it to work with only one pair of wires. It accomplishes this with only a slight (.2 km) decrease in loop length. Both HDSL and SDSL are symmetric forms of DSL technology, which means they have the same bandwidth capability in both directions. VDSL, also sometimes called BDSL, is targeted at high-access demanding companies and can support speeds of 52 Mbps downstream and 13 Mbps upstream.
ADSL (Asymmetrical) is the type of DSL being offered for high-speed Internet access. It is asymmetrical because it provides different bandwidths in the upstream and downstream directions, giving the user a much bigger "pipe" in the downstream direction. This scheme works well for the typical Internet user, where upstream communication is usually small (link requests) compared to downstream communication (Web pages with graphics, downloads). An ADSL circuit works by connecting an ADSL modem on each end of a twisted-pair telephone line, creating three information channels, a high speed downstream channel (to your computer), a medium speed upstream channel (from your computer), and a POTS voice channel. The ability to provide separate voice and data "channels" on the same line is one of the aspects of DSL technology that makes it so attractive to the telephone companies. Standard ADSL service requires the use of a "splitter" on both ends, to separate the voice channel from the data channels. One advantage of being able to split the data and voice like this is that the phone companies can keep them on separate networks. The Internet data calls can stop clogging up the PSTN (Public Switched Telephone System) and be sent directly to the packet-switched network. With the advent of G.Lite DSL, the service can now be deployed to homes without even the need for a telephone company installed splitter. Hence in addition to its other acronyms this service is often referred to as "splitterless-DSL." The exciting promise of DSL lies in this ability to implement the service easily with existing phone wiring. By being able to offer a high-speed data service that will work on your existing phone line. It can be turned on without any installation visit yielding a potential consumer audience and rate of deployment that far surpasses other high-speed options.
ADSL works well for two types of applications, interactive video and high-speed data communications. High-speed data services break out into two main areas, Internet access and remote LAN access, the realm of telecommuters. In this article we focus on using ADSL for high-speed Internet access. Besides higher bandwidth, some of the advantages of ADSL access from telephone companies are that there are no per-minute charges, and you get an "always-on" connection for your monthly fee. G.Lite ADSL was developed as a cheaper, lower bandwidth version of ADSL service, that could be turned on without a visit from a telephone technician. Companies like Microsoft, Compaq and Intel have been involved in the G.Lite effort, all hoping to establish a high-speed data service that is as easy for consumers to install as today's analog modems. In late 1998, G.992.2 was adopted by the ITU as the standard that began as the G.Lite. Formal ratification of the new G.992.2 standard is official as of June 1999. At 1.5 Mbps downstream and 386 Kbps upstream, G.Lite DSL is still 8 to 10 times faster than the ISDN services offered today for Internet access, and more than 25 times faster than 56k modems. Most providers are not yet offering G.Lite ADSL service, but you can expect this to change in the near future. If you order an ADSL service today, you will most likely still need a technician to visit and install an ADSL splitter. See ADSL, HDSL, XDSL, DSLAM, T1, T3 and ISDN. Also see CABLEMODEMINFO.COM as a pretty good source of DSL information.
A Digital Subscriber Line Access Multiplexer is a mechanism at a phone company's central location (CO) that links many customer DSL connections to a single high-speed ATM line. When the phone company receives a DSL line, an ADSL modem with a POTS splitter detects voice calls and data. Voice calls are sent to the PSTN, and data are sent to the DSLAM, where it passes through the ATM to the Internet, then back through the DSLAM and ADSL modem before returning to the customer's PC. The more DSLAMs a phone company has, the more customers it can support. Provides high-speed Internet or Intranet access over traditional twisted-pair telephone wiring through the use of ADSL technology. Provides simultaneous high-speed digital data access and POTS analog service over the same twisted-pair telephone line. Can be installed in the CO or at an ISP adjacent to the CO.
An acronym for Digital Subscriber Network. It is a network grouping of DSL lines through a DSLAM on an ATM line.
1. An acronym for Digital Signal Processor. A specific microprocessor which can be programmed to perform the mathematical algorithms involved in the digital signal processing of information. These real-time processors make up the fastest moving and developing segment of the semiconductor market and are particularly well suited to handle the demands of "right now" processing of information, such as the engine in 70 percent of the world's digital cellular phones and virtually all digital pagers and PDAs, improving automobile braking performance, or enabling faster network connections. DSPs are unique microprocessors that are programmable and operate in real time, obviously much faster than any general purpose microprocessors. The ability to crunch vast quantities of numbers, while racing a clock is the value digital signal processors bring to the electronics marketplace. Texas Instruments is a world leader in this market. See more at HTTP://WWW.TI.COM.
2. An acronym for Digital Signal Processing. The process of manipulating analog information that has been converted into a digital signal. This is useful for data compression specific applications.
The acronym for Data Set Ready. A serial connectivity term, used primarily with printers and modems in modern systems. DSR is the primary computer signal line for hardware handshaking over a serial interface; connects to the DTR line at the computer. See DTR.
An acronym for Dedicated Short Range Communication. See RFID.
An acronym for Daylight Saving (not savings....) Time. For information about it, visit the government site dedicated to it. Also see GMT and UTC.
A particular type of video display technology for laptop, portable and handheld devices. Short for Double Layer Supertwist Nematic, a passive-matrix LCD technology that uses two display layers to counteract the color shifting that occurs with conventional supertwist displays. See CSTN.
Data Space Transfer Protocol is used to index and categorize data using a XML based catalog. Data, no matter how it is stored (e.g. file, type of file, database, or distributed database), has corresponding XML files, which contain UCK (Universal Correlation Key) tags that act as identification keys. Data is retrieved when a user connects to DSTP servers with a DSTP client and asks for specific information. Data is found and retrieved based on the labels contained in the UCK tags.
An acronym and industry term for Digital Service Unit, a device used to connect a V.35 serial interface to a digital circuit. Generally any CPE that terminates a digital circuit is referred to as a "CSU/DSU".
An acronym for Document Type Definition, a type of file associated with SGML and XML documents that defines how the markup tags should be interpreted by the application presenting the document. The HTML specification that defines how Web pages should be displayed by Web browsers is one example of a DTD. XML promises to expand the formatting capabilities of Web documents by supporting additional DTDs.
An acronym for Data Terminal Equipment refers to communications hardware such as computers, terminals, and similar equipment, as opposed to DCE such as modems. See also DCE.
An acronym for Dynamic synchronous Transfer Mode, a specification that was unanimously approved by the members of ETSI, the European Telecommunications Standards Institute. The official standard document was published on May 6th, 2002. The Ethernet over DTM standard, by ETSI named ES 201 803-7, specifies how the DTM protocol transports Ethernet traffic, such as IP, in a DTM multi-service network environment. The connection-oriented DTM improves Ethernet characteristics as it provides an underlying transport layer that is able to guarantee the quality of service. The DTM specification for Ethernet transport enables multiple vendors to integrate their products with DTM systems. For example, xDSL equipment with Ethernet interface can be connected directly to a DTM backbone. Per the specification, a DTM network provides transport for all services in dynamic circuit-switched logical channels. Services such as high-quality IP video, online gaming and IP telephony can thereby be delivered over standard Ethernet interface with a minimum of delay and without interruptions. The establishment of a DTM standard is an on-going process. During the coming year additional parts are expected to be approved; the specification of DTM core signaling, video transport and specifications for physical interfaces for DTM over SDH, featuring speeds up to 40 Gbps.
1. Acronym for Dual Tone Multi-Frequency, the system used by touch-tone telephones. DTMF assigns a specific sound frequency, or tone, to each key so that it can easily be identified by a monitoring microprocessor. That frequency is then translated into a usable analog or digital signal. This is commonly known as Touch Tone.
2. Audible tones which conform to North American Telephone Standards. These are generated by push-button telephones to dial telephone numbers, as well as to provide control or data input to voice processing systems. Especially significant in the operation of most automated attendants and Fax/data line sharing devices.
The acronym for the serail connectivity term Data Terminal Ready. It is a primary serial printer signal for hardware handshaking over a serial interface; connects to the DSR pin at the computer. See DSR.
An acronym for Digital Terrestrial TeleVision, also known as DTT. This technology brings the clarity and resolution of digital TV through conventional (usually analog) methods of broadcast and media delivery, such as cable and fiber optics. It does not use satellite to deliver the programming. It is considerably higher quality than analog television and is expected to be the industry standard by the year 2005.
An acronym for Digital TeleVision. This technology brings the clarity and resolution of digital TV through conventional (usually analog) methods of broadcast and media delivery, such as cable and fiber optics. It does also use satellite to deliver the programming. It is considerably higher quality than analog television and as of 2003, is the industry standard for new broadcast technology. See SDTV for more information.
A feature that allows one to operate on either cellular or PCS frequencies.
A feature that allows one to utilize either analog or digital mode. See A/B switching. The CSGNetwork Message Transmitter sends pager and cellular messages in both analog and digital modes, based on service providers' restrictions. Try it!
1. A large mass of information that shows the exact contents of computer memory at a particular time. Dumps are used by programmers in the debugging process. Can be execute for instance by the DOS program, DEBUG.
2. To send a large volume of information to somewhere specific such as a printer or a screen.
3. A backup or a backup file created by the UNIX dump utility.
4. A tape or CD backup in a batch process.
5. The general appearance of a real programmer's work area.
A term in computer and telephony that is the ability to send (transmit) and receive at the same time, data or voice. Sometimes called full duplex. See half duplex.
A disk process somewhat similar to disk mirroring in which each of multiple storage disks has its own SCSI controller. Disk mirroring (also known as RAID-1) is the practice of duplicating data in separate volumes on two hard disks to make storage more fault-tolerant. Mirroring provides data protection in the case of disk failure, because data is constantly updated to both disks. However, since the separate disks rely upon a common controller, access to both copies of data is threatened if the controller fails. Disk duplexing overcomes this problem; the use of redundant controllers enables continued data access as long as one of the controllers continues to function.
A CPU made by AMD that is a derivitive of the AMD Athlon processor. According to AMD, the processor is designed to provide an optimized solution for value conscious business and home users. Employing an innovative design, the AMD Duron processor features a sophisticated cache architecture with 192KB of total on-chip cache; a high-speed 200MHz front-side bus, and a superscalar floating point unit with enhanced 3DNow! technology.
An acronym for Digital Versatile Disc or a more outdated version, Digital Video Disc. In reality, it is a new type of CD-ROM that holds a minimum of 4.7GB (gigabytes), enough for a full-length movie, advertisements, trailers, in and out takes, interviews, popcorn, soft drinks and candy. Many experts believe that DVD disks, called DVD-ROMs, will eventually replace CD-ROMs, as well as VHS video cassettes and laser discs. My personal opinion is that there will be a change in the primary focus and DVD will have it; there will always be a place for the other media. (Of course, I liked DIVX, 8 track and Quad discrete also!) DVD has already stood the challenge of DIVX, a competing technology from the mind of retailer Circuit City. The DVD specification supports disks with capacities of from 4.7GB to 17GB and access rates of 600 KBps to 1.3 MBps. The size and higher resolution capabilities make this an ideal format for super clear home movie presentations. One of the best features of DVD drives is that they are fully backward compatible with CD-ROMs. This means that DVD players can play old CD-ROMs, CD-I disks, and video CDs, as well as new DVD-ROMs. Newer DVD players, called second-generation or DVD-2 drives, can also read CD-R and CD-RW disks, and two technologies not yet clearly defined and not yet readily available to the general market, DVD-RAM and DVD+RW. DVD uses MPEG-2 to compress video data.
With the history of VHS and Beta in mind, this is a new type of rewritable DVD compact disc that provides much greater data storage than today's CD-RW systems for both optical and audio use. The final specifications for DVD-RAMs are still being hammered out by the DVD Consortium. Meanwhile, a competing group of manufacturers led by Hewlett-Packard, Philips and Sony, three of the biggest players in both the computer and consumer marketplaces, have come up with a competing standard called DVD+RW. Whereas the DVD-RAM standard supports 2.6 GB per disk side, DVD+RW supports 3 GB per side. In these sort of wars, the first to the market usually wins but whoever it is in this case, my money is on HP and Sony setting the standard. DVD-RAM uses a totally different kind of physical recording method, which is absolutely incompatible with DVD (hence, it can hardly be called 'DVD'). No normal DVD player will be able to read DVD-RAM discs, even if you use the newer DVD-RAM version without a cartridge housing.
See DVD. Also see DVD-RAM and DVD+RW.
DVD-R and DVD-RW were initially not designed to be used as a DVD-compatible recording solution. DVD compatibility was added at a later point, however since the formats were not developed for this purpose, they do not offer the level of compatibility and flexibility (while remaining DVD compatible!) that DVD+R/+RW offers. Furthermore, DVD-R/-RW is less suitable for data applications as well due to a number of technical limitations (such as the inability of random access writing).
DVD+R/+RW, DVD-RAM and DVD-R/-RW are all rewritable DVD formats, however, only DVD+R/+RW is designed from the start to be compatible with existing DVD-ROM drives and DVD-Video players, both on a physical as well as on a logical level. This means that a DVD+R or DVD+RW disc recorded in a DVD+R/+RW video recorder can be played in virtually all DVD-Video players or DVD-ROM equiped PCs, and that any DVD+R or DVD+RW disc recorded with data on a PC DVD+R/+RW drive can be read by most DVD-ROM drives. See DVD+RW.
In 2003, Philips and the DVD+RW Alliance announced specifications for dual-layer DVD+R discs, a technology they called DVD+R9, refering to the "DVD9" naming used for pre-recorded dual-layer DVDs. The capacity of a dual-layer disc is 8.5 GB. First products supporting this new disc format, both PC data drives and consumer DVD video recorders, began appearing in early 2004. Like DVD+RW and the existing single-layer DVD+R, DVD+R9 was designed to be fully compatible with existing DVD-Video players and DVD-ROM drives. In that respect, a recorded DVD+R9 disc should behave identically to a pre-recorded dual-layer DVD when used in read-only equipment. In IT workplaces, we feel DVD+R9 to become particularly popular in PC applications, as it allows for almost double the amount of data to be recorded (think of harddisk backups or large media files like movies or MP3s). Furthermore, it should be easier to use a DVD+R9 disc for backups of dual layer DVDs, which make up for the majority of DVD movie releases. All future DVD+R9 drives and recorders, based on the standard, will also record on DVD+RW and standard single-layer DVD+R media. Single-layer DVD+R media will remain to be available, as it suits a lot of recording purposes, and they are likely to be cheaper to manufacture. Current DVD+R/+RW drives and recorders cannot record onto DVD+R9 media, however, since DVD+R9 is fully compatible with the DVD-ROM specifications, they will be able to read those discs recorded on other equipment. See DVD+RW.
In the DVD wars, this is another standard for rewritable DVD disks being spearheaded and promoted by Hewlett-Packard, Philips and Sony. It is competing with another unfinished and unsupported standard, called DVD-RAM, developed by the DVD Consortium. The two standards are totally incompatible. DVD+RW disks have a slightly higher capacity, roughly 3 GB per side, versus about 2.6 GB per side for DVD-RAM disks.
1. An acronym for Digital Video Interface. DVI is a concerted effort specification created by the Digital Display Working Group (DDWG) in an attempt to accommodate analog and digital monitors with a single connector. The Digital Display Working Group is an open industry group lead by Intel, Compaq, Fujitsu, Hewlett Packard, IBM, NEC and Silicon Image. The objective of the Digital Display Working Group is to address the industry's requirements for a digital connectivity specification for high-performance PCs and digital displays. As of late 2008, there are five different DVI configurations. DVI-A, (which never became a standard) designed for analog signals, DVI-D (also known properly as DVI-D Single Link), designed for digital signals, and DVI-I (also known properly as DVI-I single link) the mutually integrated specification, designed for both analog and digital signals. There is also a Dual Link specific connector for either DVI-D and DVI-I. (see all the connectors here, and read some additional information about them.) The DVI connection is NOT compatible with the 20 year old VGA 15 pin connector. It is an entirely different connector that is beginning to show up on display cards and monitors as of late 2001. The original signal is pure digital but when transmitted to a DVI interface through the appropriate port, the digital signal is converted to analog if asked to do so by the program or by the monitor.
2. The acronym for Digital Visual Interface, a digital interface electronics industry standard to convert analog signals into digital signals in order to accommodate both analog and digital monitors. Data is transmitted using the transition minimized differential signaling (TMDS) protocol, providing a digital signal from the PC's graphics subsystem to the display. The standard specifies a single plug and connector that encompass both the new digital and legacy VGA interfaces, as well as a digital only plug connector. DVI handles bandwidths in excess of 160 MHz and thus supports UXGA and HDTV with a single set of links. Higher resolutions can be supported with a dual set of links.
3. An acronym for DeVice Independent, a file format used by the TeX typography system.
An alternative keyboard layout designed for speed. See QWERTY, the standard keyboard, so named for the starting letters on the upper row of the keyboard layout. The French standard is AZERTY.
1. An acronym for Digital Video Recorder. As of 2003, this is an emerging technology with no real standards as of yet. The general intent is the same is that of a VCR's online record and playback, with the exception being that the media is either solid state non-volatile memory or a disk drive. The quality of the recording and eventual playback is much higher than that of tape.
Dense Wavelength Division Multiplexing is an optical technology used to increase bandwidth over existing fiber optic backbones. DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. In effect, one fiber is transformed into multiple virtual fibers. So, if you were to multiplex eight OC -48 signals into one fiber, you would increase the carrying capacity of that fiber from 2.5 Gb/s to 20 Gb/s. Currently, because of DWDM, single fibers have been able to transmit data at speeds up to 400Gb/s. And, as vendors add more channels to each fiber, terabit capacity is on its way. A key advantage to DWDM is that it's protocol and bit-rate independent. DWDM-based networks can transmit data in IP, ATM, SONET /SDH, and Ethernet, and handle bit-rates between 100 Mb/s and 2.5 Gb/s. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel. From a QoS (Quality of Service) stand point, DWDM-based networks create a lower cost way to quickly respond to customers' bandwidth demands and protocol changes.
Unkind name (one of many) for a person with limited social and technical skills. Generally a geek wannabe. Many assembly language programmers fit right in with Dweebs.
A variation of the 80486 processor family from Intel. Often called the DX2-66, it actually came in a variety of speeds, though only the DX2-50 and DX2-66 were ever released. It has an internal bus of 33MHZ and a doubler circuit so that the CPU cycle rate was 66MHZ. The DX2-50 was based on the 80486-25DX processor while the DX2-66 was based on the 80486-33DX chip. This was renamed after the end of the run of processors to be included in a group known as Overdrive processors, though it was never called that while it was a truly active product.
A variation of the 80486 processor family from Intel. Dubbed the Overdrive processor by Intel, this was both an engineering and marketing failure. It was supposed to be a double DX2 but Intel could never get it to oscillate reliably at that speed so instead, it was a tripled DX-33 or DX-25. If properly named, they should have been called the DX3-75 and DX3-99. The flagship of the line had an internal bus of 33MHZ and a tripler circuit so that the CPU cycle rate was 99MHZ (called the 100); the DX4 lighter version had an internal bus of 25MHZ and a tripler circuit so that the CPU cycle rate was 75MHZ. The DX4-75 was based on the 80486-25DX processor while the DX4-100 was based on the 80486-33DX chip. Intel is reluctant to claim they ever made this one.
1. Type of RAM (Random Access Memory). To keep data in the Dynamic RAM memory (DRAM), this data needs to be refreshed (recharged). The electric charge fades out of a DRAM like air seeps out of a balloon. Because of this change, it is called Dynamic.
2. Refers to actions that take place at the moment they are needed rather than in advance. In the computer industry, the "jargon" that is often used for that action is "on the fly". For example, While some programs "block out" a certain amount of memory and code it into the first few lines of code in the entry routine of the program, many programs perform dynamic memory allocation, which means that they do not reserve memory ahead of time, but seize sections of memory when memory is needed. In general, such programs require less memory and tend to be more friendly with other programs, although they may run a little more slowly. The opposite of dynamic is static. A static action is pre-designated and is not changed during the execution of a program or action. Memory allocation, physical computer and device addresses, programming variables, network participation and buffering operations are all viable examples of possible dynamic or static assignments. One of the most common scenarios of this action is that many ISPs assign IP addresses in dynamic fashion, rather than the user making a static assignment to his computer. See TCP/IP.
dynamic link library
See (DLL) and .DLL.
A word coined from the phrase Dynamic Interactive Data Set. This technology is a data layer, in reality, a database acquisition table that handles, selects and sorts records as specified by a question. This technology is best integrated into SQL databases and has been made popular by new ventures into search engine input alternatives. A good example is the very well received (but legally controversial) Ask Jeeves site, HTTP://WWW.ASK.COM. The search technology is a one way street in that it is only fetching information. The technology was designed to work in a bi-directional (Bi-Di) manner in that it will also automatically reflect changes in its underlying tables and, when modified, can make changes in those tables.
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