Glossary terms provided by TechTerms.com.
| Word | Description |
| D-Link | D-Link Corporation was founded in 1986 in Taipei as Datex Systems Inc. It began as a network adapter vendor and has gone on to become a designer, developer, and manufacturer of networking solutions for both the consumer and business markets. Product Range D-Link’s products are geared towards the networking and communications market. Its business products include switches, security devices, and business wireless, whilst consumer products cover consumer wireless devices, broadband devices and the Digital Home devices (which includes media players, storage and surveillance). It was the first wired and wireless networking company to launch “green” technology, D-Link Green. D-Link first applied the power saving technology to their unmanaged switches and later on, its wireless routers. |
| Daemon | The word "daemon" actually comes from the Greek language, meaning an "inner or attendant spirit" (Oxford American Dictionary). This is a fitting name, as a computer daemon is a constantly running program that triggers actions when it receives certain input. For example, a printer daemon spools information to a printer when a user decides to print a document. A daemon running on a mail server routes incoming mail to the appropriate mailboxes. Web servers use an "HTTPD" daemon that sends data to users when they access Web pages. While daemons were first used by the Unix operating system, they have also been incorporated into Mac OS X, which is Unix-based. |
| Daisy Chain | In computer terminology, this refers to connecting one device (historically SCSI, but now USB or FireWire as well) to another device, instead of directly to a computer. In fact, you can daisy chain several SCSI devices to one another, and only one of them needs to be connected to a computer with a SCSI interface for them all to be controlled by it. |
| Dark Fiber | Fiber optic wiring that has been installed but has not been turned on yet. Often, companies that lay fiber optic cabling will lay extra cable, since the laying of miles of cable is a very costly and time consuming procedure. This dark fiber will lay dormant until the company needs extra capacity, or until it leases it to another company that needs the capacity. Then the company “lights it up” by sending optical data over the fiber. |
| DAS | Direct Attached Storage, i.e. disk storage directly connected to a computer, as opposed to NAS or SAN. |
| Dashboard | Dashboard is a user-interface feature Apple introduced with the release of Mac OS X 10.4 Tiger. It allows access to all kinds of "widgets" that show the time, weather, stock prices, phone numbers, and other useful data. With the Tiger operating system, Apple included widgets that do all these things, plus a calculator, language translator, dictionary, address book, calendar, unit converter, and iTunes controller. Besides the bundled widgets, there are also hundreds of other widgets available from third parties that allow users to play games, check traffic conditions, and view sports scores, just to name a few. The dashboard of widgets is accessed by clicking the Dashboard application icon, or by simply pressing a keyboard shortcut (F12 by default). Clicking a plus "+" icon in the lower-left hand corner of the screen provides the user with a list of all installed widgets. Clicking the widgets or dragging them onto the desktop makes them active. They can be individually closed by clicking the close box, just like other open windows. Pressing the keyboard shortcut (F12) makes them instantly disappear, removing them from view until the user needs them again. |
| Data | Computer data is information processed or stored by a computer. This information may be in the form of text documents, images, audio clips, software programs, or other types of data. Computer data may be processed by the computer's CPU and is stored in files and folders on the computer's hard disk. At its most rudimentary level, computer data is a bunch of ones and zeros, known as binary data. Because all computer data is in binary format, it can be created, processed, saved, and stored digitally. This allows data to be transferred from one computer to another using a network connection or various media devices. It also does not deteriorate over time or lose quality after being used multiple times. |
| Data Aggregation | Data Aggregation is the ability to get a more complete picture of the information by analyzing several different types of records at once. |
| Data Center | Any computing environment where there is a service agreement between the people managing the computing resources and the users. A company computer network is a data center, but so is a network at an ISP. Additionally, data center has come to mean a website or network with its resources dedicated to providing information on a particular subject. |
| Data Compression (Compression) | Takes something large and makes it smaller. Compression generally comes in two forms: lossy and lossless. Lossy compression is best used on graphics files and sound files, where loss of quality is acceptable in many situations. Lossy compression crunches down the data at a much higher ratio, at the expense of having an image or a sound that isn’t quite the same as before it was compressed. In the best scenario the data takes up less space, but the person viewing the graphic or listening to the sound file will not be able to notice. Lossless compression squeezes data down so that at some later date it can be uncompressed and returned to its exact structure. Lossless compression is best used on data files and programs. |
| Data Custodian | A Data Custodian is the entity currently using or manipulating the data, and therefore, temporarily taking responsibility for the data. |
| Data Encryption Standard (DES) | An encryption method developed by IBM in 1977. It uses a private 56-bit key that is applied to each 64- bit block of data. The sender and receiver must each know the private key. Anything encrypted by DES encryption has 72,000,000,000,000,000 (or 72 quadrillion) possible keys. DES encryption has been broken, but it took over 14,000 computers operating in succession to crank through codes until the proper key was found. See also Triple DES encryption. |
| Data Entry | A job function where the employee is expected to enter data into a computer. Typically, the only technical skill you need for such jobs is typing. Some people use data entry positions to springboard into low-end technical support and head on towards more technical jobs. |
| Data Integrity | The reliability and correctness of data. Typically the reliability and correctness of data in a database, but can apply to the reliability and correctness of data in any context. Data Integrity checks are checks or tests to confirm the integrity of data. Such tests normally verify the relationships between data as well as ensuring that data elements are within expected limits. |
| Data Management | Data management refers to the way individuals, companies, and organizations manage computer data. It includes micro applications, such as data architecture and design, as well as macro applications, including data storage, access, and security. While computer data may be intangible, it can also be valuable. Therefore, it is important for all users to consider how they manage their data. This may involve taking steps such as backing up important files and encrypting personal information. |
| Data Mining | Generic term for identifying possible relationships and trends between data items. Typically data mining is the statistical analysis of data to identify commonalities and patterns. |
| Data Owner | A Data Owner is the entity having responsibility and authority for the data. |
| Data Transfer Rate | The data transfer rate is commonly used to measure how fast data is transferred from one location to another. For example, a hard drive may have a maximum data transfer rate of 480 Mbps, while your ISP may offer an Internet connection with a maximum data transfer rate of only 1.5 Mbps. Data transfer rates are typically measured in bits per second (bps) as opposed to bytes per second, which can be understandably confusing. Because there are eight bits in a byte, a sustained data transfer rate of 80 Mbps is only transferring 10MB per second. While this is confusing for consumers, Internet service providers must enjoy measuring data transfer rates in bps since it makes their Internet access speeds sound 8x faster than they really are. |
| Data Type | A data type is a type of data. Of course, that is rather circular definition, and also not very helpful. Therefore, a better definition of a data type is a data storage format that can contain a specific type or range of values. When computer programs store data in variables, each variable must be assigned a specific data type. Some common data types include integers, floating point numbers, characters, strings, and arrays. They may also be more specific types, such as dates, timestamps, boolean values, and varchar (variable character) formats. Some programming languages require the programmer to define the data type of a variable before assigning it a value. Other languages can automatically assign a variable's data type when the initial data is entered into the variable. For example, if the variable "var1" is created with the value "1.25," the variable would be created as a floating point data type. If the variable is set to "Hello world!," the variable would be assigned a string data type. Most programming languages allow each variable to store a single data type. Therefore, if the variable's data type has already been set to an integer, assigning string data to the variable may cause the data to be converted to an integer format. Data types are also used by database applications. The fields within a database often require a specific type of data to be input. For example, a company's record for an employee may use a string data type for the employee's first and last name. The employee's date of hire would be stored in a date format, while his or her salary may be stored as an integer. By keeping the data types uniform across multiple records, database applications can easily search, sort, and compare fields in different records. |
| Data Warehouse | A large database where information is gathered from various online transaction systems. Usually, this information is put together and “mined,” as in datamining, to learn more about customers or customer purchasing habits. Data warehouses are used to gather information that may not be obvious when viewed in one context, but when grouped together in the data warehouse and properly queried, you can find out useful information. For example, a supermarket may find out that 47% of its customers buy light bulbs at the same time that they purchase shoelaces. Some of this data may be useful in a business sense, and some of it not so useful. |
| Data Warehousing | The act of putting data together in a Data Warehouse. |
| Database | A collection of related records. In computing a database is normally taken as a structured collection of records, that is managed and queried using a database management system (DBMS). |
| Database Connectivity | Connecting and communicating between an application and a database system. |
| Database Schema | The description of the tables and views in a database together with the relationships between them. |
| Datagram | Request for Comment 1594 says, "a self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network." The term has been generally replaced by the term packet. Datagrams or packets are the message units that the Internet Protocol deals with and that the Internet transports. A datagram or packet needs to be self-contained without reliance on earlier exchanges because there is no connection of fixed duration between the two communicating points as there is, for example, in most voice telephone conversations. (This kind of protocol is referred to as connectionless.) |
| Daughter Board (Daughterboard) | A circuit board that plugs into a larger circuit board, or motherboard. Often processors are contained on daughterboards, along with cache memory. For example, Intel’s Pentium II (and pre-FC-PGA Pentium III) processors shipped on a daughter board that plugs into the Slot 1 on the motherboard. |
| Daughter Card (Daughter Board) | A circuit board that plugs into a larger circuit board, or motherboard. Often processors are contained on daughterboards, along with cache memory. For example, Intel’s Pentium II (and pre-FC-PGA Pentium III) processors shipped on a daughter board that plugs into the Slot 1 on the motherboard. |
| Day Zero | The "Day Zero" or "Zero Day" is the day a new vulnerability is made known. In some cases, a "zero day" exploit is referred to an exploit for which no patch is available yet. ("day one"-> day at which the patch is made available). |
| DB | 1. Database (DB). Common abbreviation for database. The abbreviation may be applied to any form of database, and does not imply any specific type of database. 2. Decibel (dB). A standard logarithmic scale for measuring the loudness of sound. |
| DBA | 1. Database Administrator. The DBA is responsible for the day to day efficient management of a database system. 2. Decibels Adjusted. This is written as dB(A). |
| DBMS | Database Management System. The system (i.e. software) for managing a database. |
| DC | 1. Direct Current. Electrical current that flows in a single direction only, cf AC. 2. Domain Controller. |
| DDI | 1. Direct Dialling In (or Inwards). If a phone number is quoted as "DDI" then it indicates a direct dial and not via switchboard (i.e. phone and ask for an extension). Most phone numbers are DDI. 2. Device Driver Interface. |
| DDNS | Dynamic DNS. Provides a central (public) database where DNS information can be stored and retrieved. See Dynamic DNS for details. |
| DDOS | Distributed Denial-of-Service (attack). A Denial of Service attack which is launched from multiple systems. A DDOS attack works by trying to overwhelm a server by the sheer number of requests generated by each of the systems participating in the attack. |
| DDR | Double Data Rate. A type of SDRAM that provides twice the data rate of conventional SDR SDRAM, by allowing data to be read on both the rising and falling edge of each clock cycle. DDR is sometimes referred to as DDR1 to distinguish it from DDR2, which can run at higher bus speeds. |
| DDR2 | Double Data Rate x2, or double data rate DDR. Like DDR, DDR2 is a type of SDRAM that allows data to be read on both the rising and falling of each clock cycle. DDR2 allows the bus to run twice as fast as DDR, and so can achieve double the throughput. |
| DDR3 SDRAM | In electronic engineering, DDR3 SDRAM or double-data-rate three synchronous dynamic random access memory is a random access memory interface technology used for high bandwidth storage of the working data of a computer or other digital electronic devices. DDR3 is part of the SDRAM family of technologies and is one of the many DRAM (dynamic random access memory) implementations. DDR3 SDRAM is an improvement over its predecessor, DDR2 SDRAM, and the two are not compatible. The primary benefit of DDR3 is the ability to transfer at twice the data rate of DDR2 (I/O at 8× the data rate of the memory cells it contains), thus enabling higher bus rates and higher peak rates than earlier memory technologies. In addition, the DDR3 standard allows for chip capacities of 512 megabits to 8 gigabits, effectively enabling a maximum memory module size of 16 gigabytes. With data being transferred 64 bits at a time per memory module, DDR3 SDRAM gives a transfer rate of (memory clock rate) × 4 (for bus clock multiplier) × 2 (for data rate) × 64 (number of bits transferred) / 8 (number of bits/byte). Thus with a memory clock frequency of 100 MHz, DDR3 SDRAM gives a maximum transfer rate of 6400 MB/s. DDR3 is a DRAM interface specification; the actual DRAM arrays that store the data are the same as in any other type of DRAM, and have similar performance. |
| Debian | Debian (pronounced /ˈdɛbiən/) is a computer operating system composed of software packages released as free and open source software especially under the GNU General Public License and other free software licenses.[3] The primary form, Debian GNU/Linux, which uses the Linux kernel and GNU OS tools,[4] is a popular and influential GNU/Linux distribution.[5] It is distributed with access to repositories containing thousands of software packages ready for installation and use. Debian is known for strict adherence to the Unix and free software philosophies as well as using collaborative software development and testing processes.[6] Debian can be used as a desktop as well as server operating system. |
| Debug | Computer programmers, like everybody else, are not perfect. This means the programs they write sometimes have small errors, called "bugs," in them. These bugs can be minor, such as not recognizing user input, or more serious, such as a memory leak that crashes the program. Before releasing their software to the public, programmers "debug" their programs, eliminating as many errors as possible. This debugging process often takes a long time, as fixing some errors may introduce others. Debugging your windshield at a gas station is much easier than debugging a computer program. |
| Debugger | Even the most experienced software programmers usually don't get it right on their first try. Certain errors, often called bugs, can occur in programs, causing them to not function as the programmer expected. Sometimes these errors are easy to fix, while some bugs are very difficult to trace. This is especially true for large programs that consist of several thousand lines of code. Fortunately, there are programs called debuggers that help software developers find and eliminate bugs while they are writing programs. A debugger tells the programmer what types of errors it finds and often marks the exact lines of code where the bugs are found. Debuggers also allow programmers to run a program step by step so that they can determine exactly when and why a program crashes. Advanced debuggers provide detailed information about threads and memory being used by the program during each step of execution. You could say a powerful debugger program is like OFF! with 100% deet. |
| Decapsulation | Decapsulation is the process of stripping off one layer's headers and passing the rest of the packet up to the next higher layer on the protocol stack. |
| DECnet | Digital Equipment Corporation network protocol. |
| Decrypt (v. to decrypt) | The act of decoding data that has been encrypted. |
| Decryption | The act of decoding encrypted data so that it can be understood. |
| Dedicated Line | Often used to mean a telephone line used solely for your computer modem or fax machine, and not used for voice calls–although it technically could be. |
| Defacement | Defacement is the method of modifying the content of a website in such a way that it becomes "vandalized" or embarrassing to the website owner. |
| Default | 1. A defined behaviour (or value) to be taken when no other behaviuor (or value) has been specified. For example: in software procedures often take parameters and here a default value would indicate the value to use for a parameter when the caller does not explicitly provide a value to use. 2. In finance a default indicates an inability to pay a debt when it becomes due. |
| Defaults | 1. A collection of default values. For example a function may take several parameters each of which might have a default value, together these represent the defaults for that function. 2. The act of using a default value. |
| Defense In-Depth | Defense In-Depth is the approach of using multiple layers of security to guard against failure of a single security component. |
| Defrag | 1. Common abbreviation for degrament, the process of rearranging how files are stored on a disk to make them contiguous rather than scattered all over the disk. See defragment for details. 2. The name of the disk defragmentation utility included in MS-DOS and newer versions of Windows. |
| Defragment | Defragmenting your hard disk is a great way to boost the performance of your computer. Though the term "defragment" sounds a little abrasive, it is actually a simple and helpful process. After all, a defragmented hard disk is a happy hard disk. Adding and deleting files from your hard disk is a common task. Unfortunately, this process is not always done very efficiently. For example, when you delete a bunch of little files and add a new large file, the file may get broken up into mulitple sections on the hard disk. The computer will still read the newly added file as a single valid file, but the drive will have to scan multiple parts of the disk to read it. Because hard disk seek time is one of the most significant bottlenecks in a computer's performance, this can drag down your computer's speed quite a bit. If you have a ton of "fragmented" files on your hard disk, you might hear extra grinding, sputtering, and other weird noises coming from your computer. You computer does not like having fragmented files any more than you do. This is why defragmenting your hard disk is such a good idea. When you start to hear extra grinding sounds, or your computer doesn't open files as quickly as it did before, it's time to defragment. With Windows, you can use the pre-installed Intel defragment program to defragment your hard disk. You can also use a commercial software program like Norton Utilities to defragment your hard disk more efficiently and with more options. For Mac users, a disk utility such as DiskWarrior or Tech Tool Pro is the only way to do it. If you use your computer daily, defragmenting your hard drive once a month should keep the fragment-fiends away. |
| Degauss | Ever wonder what that "degauss" button on your monitor does besides make a buzzing noise and cause the screen to go crazy for a second? Though that's its main purpose, the degauss button has another useful feature. To understand it, you'll first need to know that the earth has natural magnetic fields. The magnetic charges from these fields can build up inside your monitor, causing a loss of color accuracy. Degaussing scares the bad magnetism out of the monitor and fills it with good karma. If your monitor doesn't have a degauss button, fear not -- many new monitors automatically degauss themselves. If you have a flat-panel display, there is no degauss button because magnetism doesn't build up in flat screen displays. |
| Delegate | Pointer to a function in .NET. |
| Delete | Delete is computer terminology for remove or erase. You can delete text from a document of delete entire files or folders from your hard drive. When typing a document, you can remove characters behind the cursor by pressing the delete key. If you want to remove characters in front of the cursor, you can press the smaller delete key near the home and end buttons on the keyboard. You can also remove entire sections of text by selecting the text you wish to delete and pressing either delete button on the keyboard. Files and folders can be removed from your hard drive by dragging them to the Recycle Bin (Windows) or the Trash (Macintosh) and then emptying the trash. When you delete a file, it is actually not erased, but instead the reference to the file is removed. This means deleted files are still intact until they are written over. Special utilities such as Norton Unerase can recover accidentally deleted files. |
| Dell | Dell Inc. is a multinational information technology corporation that develops, manufactures, sells, and supports personal computers and other computer-related products. Based in Round Rock, Texas |
| Denial of Service | Denial of Service is an attack on a system (typically a server or a network) that aims to crash, block or overload the system and thereby deny its services to others. A denial of service attack is illegal in most countries. |
| DEP | Data Execution Protection. DEP prevents code from executing from areas of memory that should only contain data (and not code), such as the stack and various memory pools. The rational for this is to prevent an attacker from inserting rogue code into a PC's memory and then persuading Windows to run it. To operate, DEP needs to be supported by both the Operating System and the Processor. Also known as Execution Protection, NX or No Execute. |
| Deprecated | Notice that a particular software API or interface standard is being retrained only for backwards compatibility with earlier versions and that it may be removed from future versions of the software or interface. In general an item is marked as deprecated because it has been replaced with a newer method. In any event "deprecated" should be regarded as a warning not to use the item because it may be withdrawn in future releases, and as a hint that there may be a better (or newer) way to achieve the desired effect. |
| DES | Data Encryption Standard. Algorithm for secret-key cryptography (where both sender and receiver must know the same secret key). DES uses a 56bit key to encrypt data to be transmitted, the receiver uses the same key to decrypt the data. Encrypted data cannot be decrypted without the key or brute force attack methods, which may not be viable because of the time required. |
| Desktop | Your computer's desktop is much like a physical desktop. You probably keep a number of commonly used items on your desk such as pens, papers, folders, and other items. Your computer's desktop serves the same purpose -- to give you easy access to items on your hard drive. It is common to store frequently used files, folders, and programs on your desktop. This allows you to access the items quickly instead of digging through the directories on your hard drive each time you want to open them. Both the Macintosh and Windows interfaces use the desktop as a central part of the interface. Both operating systems allow you to move items on and off the desktop as you wish and offer organization tools to arrange and clean up the items on the desktop. Yes, it would be nice if there was an option like that for a real-life desktop. You can also customize your computer's desktop with the pattern or background image of your choice. |
| Developer | A person who creates computer programs, and may specialize in one or more methods of creating computer programs, Web pages, or programming languages, such as Java, C++, or Fortran, for example. Microsoft CEO Steve Ballmar is very fond of this term, as noted when he continually stated, “Developers, developers, developers, developers …” in a now infamous speech to Microsoft personnel. |
| Device Driver | This is basically synonymous with the term “driver.” It’s a piece of software that tells an operating system specifically how to communicate with a device. For high speed devices such as 3D graphics cards, using an up-to-date device driver is important to guarantee performance and stability. |
| DFS | Distributed File System. Simplifies the process of creating a single directory hierarchy that includes multiple file servers and shared folders in a group, division or enterprise. This allows files and folders to be located on different computers but appear to users as though they are in the same directory tree. |
| DHCP | Dynamic Host Configuration Protocol. DHCP is a communications protocol where a range of IP addresses are managed centrally and assigned automatically to computers on demand. The alternative is to use static IP address where each computer is permanently allocated a fixed IP address. An advantage of DHCP (over static IP address allocation) is that it removes the burden of configuring each computer to use a unique IP address and removes the need to manually keep records on which IP address has been allocated to which computer. The disadvantage is that the IP address of a computer cannot be known in advance and its IP address may change over time. |
| DHCP (Dynamic Host Configuration Protocol) | A method of automatically assigning a TCP/IP address to a client. A DHCP server is used to dole out a TCP/IP address from a pool of TCP/IP addresses to a client that supports DHCP. When you connect to your ISP over a modem or broadband you are typically assigned a dynamic (non-static) TCP/IP address via DHCP. The big advantage to DHCP is that you don’t need to manually assign a TCP/IP address to a client–the DHCP server takes care of that. After an amount of time passes where the client does not contact the server, the server puts the TCP/IP address of the client back into the pool to be assigned to that client or any other client hat requests a TCP/IP address. The disadvantage of DHCP for the DHCP client is that the client is not guaranteed to have a particular TCP/IP address at any given time. For that you want a static IP address. |
| Diagnostics | A procedure or program that is run internally to test a piece of software or hardware and ensure that it is operating properly. For example, if R2-D2 of Star Wars decided to start running into walls, C3PO would probably make him run diagnostics on himself to try to figure out what his problem was. |
| Dial-up | A dial-up connection uses a modem to connect to an ISP or another computer. It uses standard analog phone lines to transfer data up to 56 Kbps. Before the year 2000, dial-up was the standard way to connect to Internet. However, most users now connect to the Internet is via a DSL or cable modem connection. Both cable and DSL services provide a constant connection and support data transfer speeds over 100 times faster than dial-up modems. |
| Dialog Box | As the name implies, a dialog box serves to initiate a dialog with the user. It is a window that pops up on the screen with options that the user can select. After the selections have been made, the user can typically click "OK" to enter the changes or "Cancel" to discard the selections. It is customary for menu options that include an ellipsis at the end, such as "Preferences..." or "Save As...", to open a dialog box when selected. For example, if a user selects "Internet Options..." from the Options menu in Internet Explorer, a dialog box will pop up allowing the user to choose the default home page, change the security settings, empty the browser cache, and modify several other settings. Once the selections have been made, the user can click "OK" to use the new settings, or "Cancel" to discard the changes. Some Windows programs also have an "Apply" option that activates the selections without closing the dialog box. When a user selects "Open..." from the File menu, an "Open dialog box" appears, allowing the user to browse the hard drive and other disks for files to open. When "Save As..." is chosen from the File menu, a "Close dialog box" pops up, allowing the user to type the name of the file and choose where to save it. While dialog boxes may not seem too exciting, they provide an intuitive way to communicate with the computer and are an essential part of today's computer interfaces. |
| DIB (Dual Independent Bus) | The bus architecture between Intel’s Pentium II processor, memory, and L2 cache. One bus connects the processor to L2 cache and a second connects the processor to main memory. Having two buses instead of one increases performance over single-bus architectures. In addition, the speed of the external L2 cache can scale up independently from the speed of the system bus.This allows for faster cache access. The final feature of the DIB architecture is a pipeline on the cache to the processor bus that allows multiple simultaneous cache requests. |
| Dictionary Attack | An attack that tries all of the phrases or words in a dictionary, trying to crack a password or key. A dictionary attack uses a predefined list of words compared to a brute force attack that tries all possible combinations. |
| Die size | Simply put, this is the two dimensional (length by width) measurement of a microprocessor. The thickness of the processor is not considered. Typical die sizes range between 20-500 square millimeters with most consumer processors from Intel and AMD around the 80-200 square mm mark. Smaller die size allows more chips to be created with a given amount of raw materials. |
| Differential SCSI | This type of SCSI is used to connect devices that are far apart or that may suffer from interference. Standard SCSI cabling is limited to 6 meters; differential SCSI supports distances of up to 25 meters away from the SCSI host adapter. |
| Digest Authentication | Digest Authentication allows a web client to compute MD5 hashes of the password to prove it has the password. |
| Digital | Digital information is stored using a series of ones and zeros. Computers are digital machines because they can only read information as on or off -- 1 or 0. This method of computation, also known as the binary system, may seem rather simplistic, but can be used to represent incredible amounts of data. CDs and DVDs can be used to store and play back high-quality sound and video even though they consist entirely of ones and zeros. Unlike computers, humans perceive information in analog. We capture auditory and visual signals as a continuous stream. Digital devices, on the other hand, estimate this information using ones and zeros. The rate of this estimation, called the "sampling rate," combined with how much information is included in each sample (the bit depth), determines how accurate the digital estimation is. For example, a typical CD audio track is sampled at 44.1 KHz (44,100 samples per second) with a bit depth of 16 bits. This provides a high-quality estimation of an analog audio signal that sounds realistic the human ear. However, a higher-quality audio format, such as a DVD-Audio disc, may be sampled at 96 KHz and have a bit depth of 24 bits. The same song played on both discs will sound more smooth and dynamic on the DVD-Audio disc. Since digital information only estimates analog data, an analog signal is actually more accurate than a digital signal. However, computers only work with digital information, so storing data digitally makes more sense. Unlike analog data, digital information can also be copied, edited, and moved without losing any quality. Because of the benefits digital information offers, it has become the most common way of storing and reading data. |
| Digital Archive | A digital collection for which an institution has agreed to accept long-term responsibility for preserving the resources in the collection and for providing continual access to those resources in keeping with an archive's user access policies. |
| Digital Certificate | A digital certificate is an electronic "credit card" that establishes your credentials when doing business or other transactions on the Web. It is issued by a certification authority. It contains your name, a serial number, expiration dates, a copy of the certificate holder's public key (used for encrypting messages and digital signatures), and the digital signature of the certificate-issuing authority so that a recipient can verify that the certificate is real. |
| Digital Collection | A collection consisting entirely of born-digital or digitized materials. |
| Digital Control | A control that doesn’t directly cause a physical change in something, but rather sends a signal that a processor interprets. The processor then makes the change. An example of a digital control would be a television set with buttons instead of knobs. See also Analog Control. |
| Digital Data Storage (DDS) | A storage standard used with medium cost tape media and tape drives, used mainly for small businesses and departmental backups. DDS tapes are the same size and form factor as DAT tapes used to store music digitally on tape media, but DDS media is more robust and more expensive. There are four different DDS standards: DDS-1 through DDS-4. The four standards allow for backup of 2 GB, 4 GB, 12 GB, and 20 GB worth of uncompressed (native) storage respectively. Storage sizes are typically listed as double for compressed data. DDS media is good for up to 10 years, but should not be used for more than 100 backups or it may become unreliable. DDS tapes are falling to the wayside as DLT, AIT, and other standards offer higher reliability. Sony and HP have both announced that they will not be supporting DDS-5, which pushes DDS data storage up to 40 GB of native storage per tape. |
| Digital Envelope | A digital envelope is an encrypted message with the encrypted session key. |
| Digital Linear Tape (DLT) | A technology designed by DEC and sold to Quantum used for backing up huge amounts of data (up to 35 GB per tape without compression, 70 GB with compression). The drives are very expensive and so is the media, but they are bulletproof. |
| Digital signature | A form of electronic signature that works with a public and private key encryption system and a certificate authority. To sign an electronic document with a digital signature, you use digital signature software to select the document and enter an authorization code that is unique to your digital signature. The signature consists of a string of characters and the signer’s name, title, company, certificate serial number, and the name of the certificate authority. |
| Digital Signature Algorithm (DSA) | An asymmetric cryptographic algorithm that produces a digital signature in the form of a pair of large numbers. The signature is computed using rules and parameters such that the identity of the signer and the integrity of the signed data can be verified. |
| Digital Signature Standard (DSS) | The US Government standard that specifies the Digital Signature Algorithm (DSA), which involves asymmetric cryptography. |
| Diode | An electronic device with two electrodes/terminals, one called the cathode and the other the anode, and a single PN junction (which uses part P-type and part N-type semiconductor material). The diode will conduct current in only one direction, and only when the cathode voltage is positive relative to the anode voltage by a specified amount. The specific voltage depends on which semiconductor materials the PN junction is manufactured from. Diodes are often used as a rectifier to convert AC power to DC, but they have many uses. |
| Dip Switch | One or more switches that are housed in a rectangular box on a circuit board. The switches are binary in nature, either on or off for each switch. Dip switches were more common on old ISA cards, and are often used in place of groups of jumpers. Nowadays Plug-and-Play and the abundance of Flash memory for saving settings have all but eliminated these nasty things in consumer PCs. |
| Direct Connection | A permanent connection between your computer system to a computer network. |
| Directory | A directory is another name for a folder. Files on your hard disk are organized into various folders, or directories, so that it is easier to keep track of them. For example, you may keep your pictures in one folder and your music files in another folder. Folders can also contain other folders, allowing for more specific organization. Since you can have folders within a folder, files on your hard drive are organized much like branches on a tree. The main directory on your hard drive is appropriately called the "root directory." Folders that exist within the root directory most likely contain other folders, which may branch out to even more folders. When you are browsing one directory and want to open the folder that contains the current directory, it is called "moving up a directory." As you move up directories, you will eventually move up to the root directory. In Windows, this may be your C:\ directory, while on the Mac it will be the name of your hard drive, such as "Macintosh HD." |
| DirectX | DirectX is a set of standard commands and functions that software developers can use when creating their programs. While any Windows-based software program can include DirectX commands, they are usually used in video games. For example, developers may use DirectX for controlling video playback, sound effects, and peripheral input (such as a keyboard, mouse, or joystick). By incorporating DirectX functions into a computer game, programmers can use predefined commands to manage the video and sound of their game, as well as user input. This makes it easier for programmers to develop video games and also helps the games look more uniform, since DirectX games use many of the same commands. Technically, DirectX is known as an application programming interface (API), which consists of predefined functions and commands. In order to create programs that use DirectX, software developers must use the DirectX software development kit, available from Microsoft. However, most users need only the DirectX "End-User Runtime" installed on their computer in order to run DirectX-enabled software. The DirectX API is available for Windows software and Xbox video games. |
| Disassembly | The process of taking a binary program and deriving the source code from it. |
| Disaster Recovery Plan (DRP) | A Disaster Recovery Plan is the process of recovery of IT systems in the event of a disruption or disaster. |
| Disc at Once (DAO) | This is a single-session method of writing data to a CD-R/RW disc that creates a disc in a format suitable for commercial duplication. Basically, the entire disc is written at once in contrast to Track at Once. |
| Discretionary Access Control (DAC) | Discretionary Access Control consists of something the user can manage, such as a document password. |
| Disk Drive | Often, this is a synonym for hard drive, but it can also refer to a floppy drive or any type of removable drive that uses magnetic media. |
| Disk Duplexing (RAID 1) | There are two forms of RAID 1: disk duplexing and disk mirroring. Disk mirroring involves two hard drives that are on the same drive controller. The same data is written to both drives, so write operations are slower because you must write data to two drives. Read operations are the same speed, as if you only had one drive. Disk duplexing is much like disk mirroring, but each drive is on a separate controller. This speeds up the normally slow write operations and also adds an additional level of redundancy, in case one of your controller cards dies. With RAID 1 you get half the space you paid for because you’re writing twice as much data. |
| Disk Image | A disk image is a software copy of a physical disk. It saves the entire data from the disk, including the file structure and all files and folders from the disk, in a single file. Because disk images are exact copies, or "clones," of original disks, they can be used to duplicate disks or serve as full backups in case a system restore must be done. Disk images can be created from both hard disks and optical media, such as CDs and DVDs. However, optical media images are technically called "disc images" instead of "disk images." Several programs, such as Nero, IsoBuster, and Norton Ghost can be used to make disk images for Windows. Programs like Apple Disk Utility and Roxio Toast can create disk images for Mac OS X. Most disk image files store data in a raw, binary format. This means they do not have a file system, which tells the computer how to access the files and folders in the disk image. Therefore, in order for the data in a disk image to be readable by the computer, the image must first be mounted by either the operating system or a disk utility program. File extensions: .ISO, .BIN, .DMG |
| Disk Mirroring (RAID 1) | There are two forms of RAID 1: disk duplexing and disk mirroring. Disk mirroring involves two hard drives that are on the same drive controller. The same data is written to both drives, so write operations are slower because you must write data to two drives. Read operations are the same speed, as if you only had one drive. Disk duplexing is much like disk mirroring, but each drive is on a separate controller. This speeds up the normally slow write operations and also adds an additional level of redundancy, in case one of your controller cards dies. With RAID 1 you get half the space you paid for because you’re writing twice as much data. |
| Disk mode | Disk mode A property of a virtual disk that defines its external behavior but is completely invisible to the guest operating system. There are three modes: persistent (changes to the disk are always preserved across sessions), nonpersistent (changes are never preserved), and undoable (changes are preserved at the user's discretion). Disk modes may be changed from the Configuration Editor's IDE Drives or SCSI Drives panels. For a detailed explanation of disk modes refer to this tech note if your host operating system is Linux or this tech note if you have a Windows NT or Windows 2000 host. |
| Disk Operating System (DOS) | This OS is what got it all started for PCs. It was produced by Microsoft and was a 16-bit command line (non-GUI) operating system, designed to run on 16-bit chips. It was still used for years on 32-bit chips. Today you can find a similar command line interface in all Windows products for quick and easy mouse-less file manipulation by running the “cmd” command. |
| Disk Striping (RAID 0) | Also known as disk striping, this form of RAID combines two or more hard drives into a single logical drive. Any data is written in blocks first to one drive, then the next, and so on. A RAID 0 configuration sacrifices redundancy for raw speed. The more drives you use the faster your logical drive will be. The space available on the logical drive is the sum of space on all of the drives used, assuming that all drives are the same size. If drives are of disparate sizes, RAID 0 generally only uses a piece of the drive equal to the smallest drive. Of course, if one drive dies, you lose all of the information on the entire RAID. Use RAID 0 with care. |
| Disk Striping with Parity (RAID 5) | A RAID 5 configuration utilizes three or more hard drives and stripes the data across them, much like RAID 0. The difference is that parity information is striped across the drives as well, so if you lose any one drive the information can be reconstructed from the parity information. For example, with three drives the first stripe is data (on drive 1), data (on drive 2), parity (on drive 3); then data, parity, data; then parity, data, data. This pattern continues. If one drive fails, you get a mix of parity and data on the remaining two drives, and you can reconstruct all of the data. Of course, before the data is reconstructed the RAID operates in “degraded mode” and is slow. To reconstruct the data you must remove the failed drive and replace it with another, or use a “hot spare.” During reconstruction the array continues to be slow. Once the RAID is reconstructed performance returns to normal levels. RAID 5 performance is similar to RAID 0 performance, but a bit slower due to the parity information. Performance increases, like RAID 0, when more drives are added. With RAID 5 you get most of the space that you’ve paid for, minus one drive’s worth. A common option with RAID 5 is the hot spare, where a drive sits idle until needed. If you lose a drive, the hot spare takes over and the RAID is rebuilt automatically. Of course you still get the performance penalty during the rebuilding stage, but it can be set to happen automatically. |
| Disk Thrashing | On a system with Virtual Memory, pages of memory are read from and written to the swap file as necessary. Disk Thrashing is when there is excessive paging, specifically when the I/O system is busy paging memory but the CPU is not fully utilized - generally if the system is unresponsive (i.e. slow) and there is lots of disk activity then the system is likely to be thrashing. If disk thrashing is a problem then a short term solution may be to reduce the number of running applications. A longer term solution is to add more memory. Also known as Thrashing. |
| diskette | Also referred to as a "floppy disk;" a portable magnetic disk most often used for secondary file storage. Current floppy disks are usually 3 1/2 inches in size with a storage capacity of up to 1.44 MB. |
| Disruption | A circumstance or event that interrupts or prevents the correct operation of system services and functions. |
| Distance Vector | Distance vectors measure the cost of routes to determine the best route to all known networks. |
| Distributed File System (DFS) | A Microsoft technology introduced in Windows 2000 that allows multiple servers and shared directories on a network to appear as a single network drive, thus helping to ease the annoying problem of running out of drive letters in complex environments. With DFS, you can have your users’ H: drive, for example, be a collection of network resources instead of just a single share. |
| Distributed Scans | Distributed Scans are scans that use multiple source addresses to gather information. |
| DLL | Dynamic Link Library. A shared library that can be loaded once by the operating system but used simultaneously by different processes and applications. Typically these have the file extension .dll. |
| DMA | Stands for "Direct Memory Access." DMA is a method of transferring data from the computer's RAM to another part of the computer without processing it using the CPU. While most data that is input or output from your computer is processed by the CPU, some data does not require processing, or can be processed by another device. In these situations, DMA can save processing time and is a more efficient way to move data from the computer's memory to other devices. For example, a sound card may need to access data stored in the computer's RAM, but since it can process the data itself, it may use DMA to bypass the CPU. Video cards that support DMA can also access the system memory and process graphics without needing the CPU. Ultra DMA hard drives use DMA to transfer data faster than previous hard drives that required the data to first be run through the CPU. In order for devices to use direct memory access, they must be assigned to a DMA channel. Each type of port on a computer has a set of DMA channels that can be assigned to each connected device. For example, a PCI controller and a hard drive controller each have their own set of DMA channels. |
| DMI | Desktop Management Interface. This is a method for managing computers in an organisation. The main component, the Management Information Format Database (MIFD), is a database that contains all the information about the local computer and its components. |
| DMI Pool | The set of data about a computer and its components, including partition data for your hard drive. When a PC boots it will display the message, “Verifying DMI Pool,” and if it will not boot past this it typically means your motherboard is not able to access your hard drive properly. This can be caused by a wrong BIOS setting for your hard drive (try “Auto”) or a non-bootable floppy disk if your floppy drive is set to boot first. |
| DMZ | Demilitarised Zone. A computer within a DMZ is unprotected by a firewall and typically any port accesses are routed through to that computer. A router will forward all traffic to the computer in the DMZ if it does not otherwise have a rule for how to forward traffic on a given port. (The computer within the DMZ may still be protected by its own separate firewall.) |
| DMZ (DeMilitarized Zone) | A part of a network that is protected by a firewall, but may be accessed by external Internet clients. The DMZ generally contains servers such as SMTP servers, remote access machines. or webservers. Client machines and internal servers that do not need to be accessed by Internet clients are kept in a more protected segment of the network than the DMZ. Alternately, DMZ can be used to refer to the media layer where route peering is done among multiple administrative regions with their own traffic policies. |
| DNS | Domain Name Service or Domain Name System. Provides hostname to IP address translations. See also A Records, CNAME. |
| DNS (Domain Name Service) | This service maps TCP/IP numbers, such as 123.12.4.245, to a more easily remembered name, such as www.geek.com. Thus, when you type www.geek.com into your browser, it goes out to the DNS server specified by your ISP and asks for a matching TCP/IP address.If the browser finds a DNS entry for the name you typed in, you see the appropriate website. If not, it lets you know. Every domain name that is actually being used for a website has a corresponding TCP/IP address. When you set up a site you have your ISP add a DNS entry to its DNS servers (or manage it yourself). This entry gets replicated across the Internet in a matter of hours, and, once fully replicated, you can reach your website from any Internet connection. |
| DNS Entry | The DNS routing tables are filled with DNS entries that map TCP/IP addresses to more easily recognized names. If your browser says it can’t find a particular DNS entry, here are some possible reasons: you may not be able to communicate with your DNS server, the site may not be responding, or your connection is broken. If a DNS server really doesn’t have the entry, there may be nothing mapped to that particular domain name address. If the domain name was just set up, the entry may not have fully replicated to your DNS server. Remember, people can own a domain name and not have an entry for it on any DNS server if they are not paying an ISP to host it. |
| DNS Record | DNS records are stored in zone files and are used for translating domain names to IP addresses. They also contain other data, including the domain name's name server and mail server information. If there are domain name aliases, such as the commonly used "www" preceding the domain name, these will also be listed in the DNS record. A typical DNS record may look something like this: ; Nameservers ; IN NS ns1.4servers.com. ; 123.456.789.01 IN NS ns2.4servers.com. ; 123.456.789.02 ; ; Domain Mail Handlers ; yourdomain.com. IN MX 0 mail yourdomain.com. IN MX 10 mail ; ; ; hosts in order ; yourdomain. IN A Your.IP.XXX www IN A Your.IP.XXX smtp IN CNAME www pop IN CNAME www ftp IN CNAME www mail IN A Your.IP.XXX ; ; end Since DNS records are made up entirely of text, they are easy to modify when needed. However, one small typo could redirect a domain name to the wrong Web server or prevent it from showing up at all. This is why it is important to enter DNS information accurately and double-check your changes entry before saving the zone file. |
| DNS Server | DNS Server A server providing DNS name translations. A DNS Server translates from names to IP Addresses. A DNS Server on a LAN will provide translations from local computer names to their IP addresses, and forward requests for unrecognised names to external DNS servers for name resolution. Also known as a nameserver. |
| DNSBL | DNS Block List. A DNSBL is a list of DNS entries from which incoming emails should be blocked. Also known as a DNS Black-hole List. DNSBLs typically list open relays and servers which can be used for RNDR attacks. These are typically used as a means to reduce spam by blocking emails from known (or likely) spammers. However, it should be appreciated that DNSBL works on listing IP addresses and does not provide any intelligent filtering based on the content of an email. DNSBL can be created and customised within a company, but there are also third party DNSBL services available on the internet. DNSBL are sometimes also referred to as RBL or simply BL. |
| Dock | The Dock is a feature of the Mac OS X Finder that provides quick access to programs, files, and folders. By default, the Dock sits at the bottom of the screen, though it can be moved to the left or right and can be hidden if preferred. It contains application icons on the left side and files and folders on the right. You can open programs and files directly from the Dock and can add or remove items by dragging the corresponding icons to or from the Dock. |
| Document | A document, or web document, is a resource on the World Wide Web that has a distinct web address. It could be an embedded image, whole web page, pdf or any other component of a web page. A document can be any kind of MIME type. |
| Domain | While the term "domain" is often used synonymously with "domain name," it also has a definition specific to local networks. A domain contains a group of computers that can be accessed and administered with a common set of rules. For example, a company may require all local computers to be networked within the same domain so that each computer can be seen from other computers within the domain or located from a central server. Setting up a domain may also block outside traffic from accessing computers within the network, which adds an extra level of security. While domains can be setup using a variety of networking software, including applications from Novell and Oracle, Windows users are most likely familiar with Windows Network Domains. This networking option is built into Windows and allows users to create or join a domain. The domain may or may not be password-protected. Once connected to the domain, a user may view other computers within the domain and can browse the shared files and folders available on the connected systems. Windows XP users can browse Windows Network Domains by selecting the "My Network Places" option on the left side of an open window. You can create a new domain by using the Network Setup Wixard. Mac users using Mac OS X 10.2 or later can also connect to a Windows Network by clicking the "Network" icon on the left side of an open window. This will allow you to browse local Macintosh and Windows networks using the SMB protocol. |
| Domain Hijacking | Domain hijacking is an attack by which an attacker takes over a domain by first blocking access to the domain's DNS server and then putting his own server up in its place. |
| Domain Name | The unique name that identifies an Internet site. Domain Names always have 2 or more parts, separated by dots. The part on the left is the most specific, and the part on the right is the most general. A given machine may have more than one Domain Name but a given Domain Name points to only one machine. |
| Domain Suffix | A domain suffix is the last part of a domain name and is often referred to as a "top-level domain" or TLD. Popular domain suffixes include ".com," ".net," and ".org," but there are dozens of domain suffixes approved by ICANN. Each domain suffix is intended to define the type of website represented by the domain name. For example, .com domains are meant for commercial websites, whereas .org domains are to be used by organizations. However, since any entity can register domain names with these suffixes, the domain suffix does not always represent the type of website that uses the domain name. For example, many individuals and organizations register .com domain names for non-commercial purposes, since the .com domain is the most sought after. Each country also has a unique domain suffix used for websites within the country. For example, Brazilian websites may use the .br domain suffix, Chinese websites may use the .cn suffix, and Swedish websites may use the .se suffix. These country-based TLDs, sometimes referred to as "country codes," are also used by international websites for defining the language of website. For example, the German home page for Google is "www.google.de" instead of "www.google.com." |
| Dongle | This funny-sounding computer term has two widely different definitions that are completely unrelated: 1. A security key. This is a little hardware device that plugs into the serial or USB port of a computer. Its purpose is to ensure that only authorized users can use certain software applications. If you have never seen a dongle, don't be surprised. They are only used with expensive, high-end software programs that most people have never heard of, much less use. When a program that comes with a dongle runs, it checks the dongle for verification as it is loading. If it doesn't find the dongle, the computer explodes. Well, not really -- usually the program just quits. If more than one application requires a dongle, multiple dongles using the same port can be daisy-chained together. Basically, if you ever find yourself daisy-chaining multiple dongles together, you must be doing pretty well in life. 2. A laptop Ethernet card adapter. This is a little connector that attaches to a PC card in a laptop on one end, and to an Ethernet cable on the other end. Since most PC (or PCMCIA) network interface cards are too small to connect directly to a standard RJ-45 Ethernet cable, they need this little adapter that connects the card to the cable. (3Com cards that use an "X-Jack" connector do not need a dongle.) As far as why the name dongle is used, I have no idea. |
| DOS | 1. Disk Operating System. The original command line based operating system used on IBM personal computers and compatibles. Technically PC-DOS refers to the version of DOS used on IBM computers and MS-DOS the version of DOS used on compatible clones from other manufacturers. Both PC-DOS and MS-DOS were written by Microsoft and were essentially identical. DOS predates Windows. Earlier versions of Windows (notably Windows 9x) provided the option to restart in "DOS mode". Current Windows versions still support a "Command Prompt", which provides a DOS like interface. |
| double buffering | This programming technique uses two buffers to speed up any computer task when the hardware can process and push information around at the same time. In graphics cards, double buffering is often used to store the next frame in a video clip in an offscreen frame buffer while displaying the current frame. This way, when the present frame is finished, the next frame is ready to write to the displayable portion of the buffer. See also: frame buffer |
| Double Click | Double clicking involves clicking your mouse button quickly two times. To perform a double click, and not just two clicks, the mouse button must be pressed twice within a very short time, typically about half a second. Most operating systems allow you to lengthen or shorten the maximum time allowed for a double click, using the Mouse Control Panel or System Preference. A double click is recognized by your computer as a specific command, just like pressing a key on your keyboard. Double clicking is used to to perform a variety of actions, such as opening a program, opening a folder, or selecting a word of text. In order to double click an object, just move the cursor over the item and press the left mouse button quickly two times. |
| Down | In computing "Down" is usually used to mean "Off", "not working" or "not available". For example "the database is down" is a statement that the database is not available for use and the statement "to power down" means to shutdown and power off. cf Up. |
| Download | To receive (or copy) data from a remote computer to a local computer via a network, modem, serial or parallel cable. For example to copy a file from a server on the internet to the local computer you are said to be downloading the file. cf Upload. |
| Downstream | The downloading (receiving) of data from the Internet to a client machine. Downstream speeds are typically much greater than upstream speeds in high speed consumer Internet connections such as cable modems and ADSL. |
| DPI | Dots Per Inch. A measure of the resolution of scanners, printers and display devices. |
| Dr. Watson | This is diagnostic software that runs automatically in Windows NT/2000/XP and can be turned on in Windows98/Me. Dr. Watson takes over when a program crashes and writes a snapshot of information about the crash to disk. |
| Drag | You can use your mouse to drag icons and other objects on your computer screen. Dragging icons from your desktop or an open window to another folder will move the objects to the new folder. You can also drag icons to the Trash (Mac) or the Recycle Bin (Windows) if you want to delete tehm. Some word processing programs allow you to select text and drag the selected text to another place in the document. To select the text, you may have to "drag" the mouse over the text you want to select. Dragging is an important technique for using today's graphical user interfaces (GUIs). In fact, there are many other things you can drag besides icons. For example, you can drag the top of windows to reposition them, you can drag the scroll bar in open documents or Web pages to scroll through them, and you can drag messages to different folders in your mail program. Other programs, such as video games and image-editing programs use dragging to reposition items on the screen. To drag an item, first move the cursor over the item you want to drag. Then click and hold down the left mouse button to "grab" the item. Move the mouse to position the item where you want it. Let go of the mouse button once you have moved the item to "release" it. This technique is known as a "drag and drop." |
| drag and drop | The act of clicking on one icon and moving it on top of another icon to initiate a specific action. Example: Dragging a file on top of a folder to copy it to a new location. |
| DRAM | Dynamic Random Access Memory (Dynamic-RAM). |
| Drive Bay | This is usually a 5.25″ wide 1″ tall hole in a computer case suitable for the installation of some sort of drive. Some are exposed so that a removable drive (e.g., floppy, CD-ROM) can fit. Some are not exposed and are meant for hard drives that users don’t need access to. |
| Driver | A driver is software that works to communicate between an operating system and a peripheral. Think of it as a translator. If you use a crappy driver, your OS won’t understand your video card and may become unstable and crash. Hardware manufacturers constantly update drivers to make them faster and more stable. Operating systems typically come with a set of drivers, but peripherals newer than your operating system typically require new drivers which must be installed via CD-ROM, floppy, or downloaded from the Web. |
| Driver Software | Software used to make computer peripherals function. Driver software is written specifically for the device to allow it to work with a particular operating system of the computer. If you upgrade your computer operating system, such as moving from Windows 98 to Windows XP then you will normally require new driver software for each of your peripherals. However, depending on the peripheral, more modern versions of Windows may already come supplied with the necessary drivers. |
| DRM | Stands for "Digital Rights Management." DRM refers to a collection of systems used to protect the copyrights of electronic media. These include digital music and movies, as well as other data that is stored and transferred digitally. For example, the Apple iTunes Music Store uses a DRM system to limit the number of computers that songs can be played on. Each audio file downloaded from the iTunes music store includes information about the owner of the file and how many times the file has been transferred. The protected files will not play on computers that have not been authorized to play the music. Digital Rights Management is important to publishers of electronic media since it helps ensure they will receive the appropriate revenue for their products. By controlling the trading, protection, monitoring, and tracking of digital media, DRM helps publishers limit the illegal propagation of copyrighted works. This can be accomplished by using digital watermarks or proprietary file encryption on the media they distribute. Whatever method publishers choose to employ, DRM helps them make sure that their digital content is only used by those who have paid for it. |
| Dropdown Menu | A type of menu that appears as a text box with an arrow pointing down in part of the box. It allows a user to click on it, and a list of choices appear below the menu. After the information drops down, one of the items can be selected. It’s possible that the information appears above the menu if there is not space below it. |
| DRP | Disaster Recovery Plan. A contingency plan covering how a business should recover from potential disasters disaster and continue functioning. Occasionally referred to as a Business Continuity Plan (BCP). |
| Drum | The part of a laser printer onto which the laser produces an electrostatic image. The drum is then rolled in toner and that toner is transferred to paper with pressure and heat. Most drums are coated with selenium for its electrical properties. Selenium is a nonmetallic element in the sulfur family, and it allows the drum to hold a charge and attract toner. |
| DS-0 (Digital Signal level 0) | The signal used to carry a standard analog or digital phone line connection. 24 DS-0 connections can be carried on a T1 line. The speed of the line is either 64Kbps, or 56Kbps if the eighth bit is used for signaling information |
| DS-1 (Digital Signal level 1) | Synonym for T1. |
| DS-2 (Digital Signal level 2) | Synonym for T2. |
| DS-3 (Digital Signal level 3) | Synonym for T3. |
| DS-4 (Digital Signal level 4) | Synonym for T4 |
| DS-5 (Digital Signal level 5) | Synonym for T5. |
| DSL | (Digital Subscriber Line) A method for moving data over regular phone lines. A DSL circuit is much faster than a regular phone connection, and the wires coming into the subscriber's premises are the same (copper) wires used for regular phone service. A DSL circuit must be configured to connect two specific locations, similar to a leased line (howeverr a DSL circuit is not a leased line. A common configuration of DSL allows downloads at speeds of up to 1.544 megabits (not megabytes) per second, and uploads at speeds of 128 kilobits per second. This arrangement is called ADSL: Asymmetric Digital Subscriber Line. Another common configuration is symmetrical: 384 Kilobits per second in both directions. In theory ADSL allows download speeds of up to 9 megabits per second and upload speeds of up to 640 kilobits per second. DSL is now a popular alternative to Leased Lines and ISDN, being faster than ISDN and less costly than traditional Leased Lines. |
| DSP | Digital Signal Processing. |
| DST | Daylight Saving Time. A system where the local clocks are advanced by an hour during the summer to make better use of the sunlight hours. Also known by different names in different countries, although "Summer Time" is common (e.g. BST = British Summer Time). In Europe (according to the European directive 2000/C 337 E/18) the official change time is 01:00 hours GMT. It is 02:00 hours in America. |
| DTD | 1. Data Type Definition. 2. Document Type Definition. A document that formally specifies for an an XML schema the XML elements, their attributes and their syntax. Given a DTD an XML parser should then be able to parse the XML document for which the DTD relates. |
| DTD (Document Type Definition) | Stands for "Document Type Definition." A DTD defines the tags and attributes used in an XML or HTML document. Any elements defined in a DTD can be used in these documents, along with the predefined tags and attributes that are part of each markup language. The following is an example of a DTD used for defining an automobile: ]> The above DTD first defines the header of the item as "Car Details." Then it provides elements to define the make and model of the automobile. The "#PCDATA" data type means it can be any text value). The "ATTLIST" tag on the next line provides options for a specific element. In this case, it states that the model can have either two or four doors. The DTD then provides elements for the year and engine type of the car, followed by a choice of either a manual or automatic transmission for the engine. The above example is a basic DTD that only uses a few data types. Document type definitions used for large XML databases can be thousands of lines long and can include many other data types. Fortunately, DTDs can be easily modified in a text editor whenever changes need to be made. |
| Dual boot | A system that can boot to two different operating systems. Some OSes, such as Windows NT/2000/XP and versions of Linux, allow for dual booting when installed. Of course, you can also use other methods, such as commercial programs that install a special boot partition that is capable of launching operating systems from other partitions. You can also boot to many more than two operating systems on the same machine. |
| Dual-Core | A dual-core processor is a CPU with two processors or "execution cores" in the same integrated circuit. Each processor has its own cache and controller, which enables it to function as efficiently as a single processor. However, because the two processors are linked together, they can perform operations up to twice as fast as a single processor can. The Intel Core Duo, the AMD X2, and the dual-core PowerPC G5 are all examples of CPUs that use dual-core technologies. These CPUs each combine two processor cores on a single silicon chip. This is different than a "dual processor" configuration, in which two physically separate CPUs work together. However, some high-end machines, such as the PowerPC G5 Quad, use two separate dual-core processors together, providing up to four times the performance of a single processor. While a dual-core system has twice the processing power of a single-processor machine, it does not always perform twice as fast. This is because the software running on the machine may not be able to take full advantage or both processors. Some operating systems and programs are optimized for multiprocessing, while others are not. Though programs that have been optimized for multiple processors will run especially fast on dual-core systems, most programs will see at least some benefit from multiple processors as well. |
| Dualscan | A passive matrix LCD screen that uses a better method of displaying graphics, producing a sharper, more vivid image than standard passive matrix screens. |
| Due Care | Due care ensures that a minimal level of protection is in place in accordance with the best practice in the industry. |
| Due Diligence | Due diligence is the requirement that organizations must develop and deploy a protection plan to prevent fraud, abuse, and additional deploy a means to detect them if they occur. |
| Dumb Terminal | These are hooked up to mainframes, and are little more than a monitor attached to a keyboard. All they are good for is running programs using the mainframe’s hard drive and memory, thus the “dumb” in the name. |
| DumpSec | DumpSec is a security tool that dumps a variety of information about a system's users, file system, registry, permissions, password policy, and services. |
| Dumpster Diving | Dumpster Diving is obtaining passwords and corporate directories by searching through discarded media. |
| Duplex | A telecommunications term that describes part of the communications between a local modem and a remote computer. In full duplex mode, the remote computer is set up to return the characters that are sent to it so that they can be displayed on your screen. In half duplex mode, the remote computer does not return the characters sent to it. Also see full duplex and half duplex for descriptions of the those terms in other contexts. |
| DVD | Digital Video Disk, or Digital Versatile Disk. DVDs have varying capacities from 4.7GB to 17GB. A conventional single layer recordable DVD will hold up to 4.7GB of data per disk. A recordable dual-layer DVD will hold up to 8.5GB of data. Dual-layering allows two layers to be stored on the same side of the DVD. When playing a DVD there is normally a slight pause when the DVD player switches layers (as the laser repositions to read the second layer). |
| DVI | 1. Digital Visual Interface. An interface between a PC graphics card and a monitor (or other display device) that is completely digital. Being completely digital there is no digital to analogue conversion involved, there is no signal loss that such a conversion would otherwise introduce. DVI is commonly used as a connection standard for HDTVs. |
| DWORD | Double-Word, meaning two words or typically four bytes. |
| Dynamic DNS | Dynamic DNS Dynamic Domain Name Service (or Dynamic Domain Name System). DNS. Dynamic DNS provides a central (public) database where DNS information can be stored and retrieved. It allows those using a dynamic IP address (i.e. one where it changes each time the computer connects to the internet) to be registered centrally so others can connect to it by name (using standard DNS). Commonly abbreviated to DDNS. |
| Dynamic Website | A dynamic website contains Web pages that are generated dynamically. Each time a user accesses a page within a dynamic site, the HTML is generated in real-time and is sent to the user's Web browser. The content is typically accessed from a database, which is why dynamic websites are often called "database-driven" sites. Most large sites contain dynamic content, while smaller sites may be designed as static websites. |
