[#da15]: DA-15 (“DA15”)

The phrase is often written both with and without a hyphen: e.g. DA-15 or DA15.

This has been one of the standards used for MIDI ports. (Another standard used for MIDI ports has been a DIN standard.) This standard has also been used for a “game port” meant to be used with a joystick (or a gamepad). Such game ports are often referred to as Game/MIDI ports. AUI networking connectors use a variation of DE15: The shell and the pins are identical, although a latch is used instead of the more typical method to help keep the connection solid, which was to use screws.

About the game ports: these ports typically supported eight directions and four buttons. The general intent there was to use four directions and two buttons on one controller, and four buttons and two buttons on a second controller. Gravis released the Gravis Gamepad which was one controller that had four directions and four buttons: the second two buttons on this first controller used the same electrical signals as the buttons on a second controller. Gravis also went on to create a Gravis GRiP standard which involved using connectors that looked like a standard game port, but even more buttons and even controllers could use this. The Gravis Gamepad Pro had a variation which supported a standard game port and also supproted GRiP. (There was also a USB version of the Gravis Gamepad Pro.) The game ports were most commonly white or black, even though “gold” was the color specified by the PC System Design Guide standard known as PC 99. Since many, and probably most, game ports were made before that standard became widely adopted, or even invented, the number of game ports that follow that standard may actually be a minority. After the standard, USB game pads started to become more common than in the marketplace than gaming devices using game pads, and a return to using plugs with game ports on them seems to be unlikely as gamers have become used to using wireless controllers. (For example, wireless Xbox 360 controllers can be used with Microsoft's official USB adapter.)

[#dac]: DAC
Digital to Analog Converter
e.g. converting a binary signal of sound into an audio wave form that may be played by standard speakers
Descretionary Access Control
Related to computer security
[#data]: data

Information. More technically, data may be used as the plural form of “datum”, where a “datum” refers to a piece of information.

Many people prefer to pronounce the term as “dat-ah”, considering that to be more correct. Others prefer “date-ah”, perhaps influenced by the famous android character from Star Trek: The Next Generation. (The same is true with the first two syllables of the word “database”.)

(See data)
[#dccp]: Datagram Congestion Control Protocol (“DCCP”)
RFC 4336: “Problem Statement for the Datagram Congestion Control Protocol (DCCP)” is introductory text describing the general purpose of this protocol (according to Wikipedia's article for “Datagram Congestion Control Protocol), and RFC 4340: “Datagram Congestion Control Protocol (DCCP)” describes further. This protocol is a Transport Layer protocol, and is mentioned by IANA's list of TCP port numbers and UDP port numbers.
[#db]: DB

The term “database” is often abbreviated as “db”.

[#dsubbshl]: DB shell used with D-sub ports

Another use of DB may refer to DB-25 or DB-9, although the term DB-9 generally refers to the DE-9 standard. Both of these phrases are often written both with and without a hyphen: e.g. DB-25 or DB25.

The term “DB-9” (or “DB9”) would suggest a DB-sized shell with 9 pins, although the phrase DB-9 usually refers to a DE-9 port. (This is discussed slightly further in the glossary entry for DE-9.) An Amiga's 23-pin port may be called a DB-23 even though its shell is not quite as wide as a DB-25 shell.

The DB-25S/DB-25F (DB-25 socket/female) connector has been found on many older computers. In older times the most common color may have been black, although in more recent times fuchsia (pink/purple) may have become a more standardized color. This was known as a “parallel port”, as multiple pins could be used simultaneously, a.k.a. “in parallel”, to transmit data. The most common thing to plug into a DB-25S/DB-25F (DB-25 socket/female) is a cord which had a DB-25P/DB-25M (DB-25 plug/male) on one end of the cord, and the male portion of an Amphenol 36-pin micro-ribbon parallel interface, more commonly known as a Centronics connector, on the other end. Many printers came with that Centronics interface, or some rather compatible plug such as HP Bitronics or IEEE 1284. These connectors have become less common because they could not carry as much data as quickly as the as newer connector types like USB, and this fact actually bottlenecked the speed that some printers could print some data. As newer printers tended to support newer connectors, eventually these parallel ports stopped being included on as many computers.

The DB-25P/DB-25M connectors built into the back of computers (either attached via a ribbon to a card in the computer, or built directly on the back of a card) are typically serial ports. A slightly odd thing is that the DB-25 serial ports have the male end on the computer, while DE9 serial ports have the male end on the computer. (Computers may also have DB-25S/F ports and DE9P/M ports, but neither of these are serial ports.) So to determine whether a serial port has the male or female end on a computer will depend on the size of the shell, whether it is DB-25 or DE9.

dB : decibel
See: decibel
[#dccpabbr]: DCCP
See: Datagram Congestion Control Protocol.
[#deprecat]: deprecate

After an organization deprecates a term or technology, the deprecated ways of doing things are not recommended for newer projects. Guidelines for Use of Extended Unique Identifier (EUI), Organizationally Unique Identifier (OUI), and Company ID (CID) (PDF file from IEEE), page 17 says that something that gets deprecated “(e.g., identifier, mapping, requirement, recommendation, process, etc.) shall not be used in any new applications. Legacy uses may be preserved”... “remove deprecated terms should be done as soon as practical. In addition, new equipment and new designs are not to use the deprecated item, except to remain compliant to the relevant standard. Existing equipment and deployed equipment need not be modified to not use the deprecated item.”

[#disc]: disc

The word refers to a flat and round object. Americans have generally used the word “disk”, although a notable exception is when referring to optical media, when the word “disc” has been used instead.

[#disk]: disk

The word refers to a flat and round object. The British have a similar word, “disc”. Americans have generally used the word “disk”, although a notable exception is when referring to optical media, when the word “disc” has been used instead.

[#ddos]: Distributed DoS (“DDoS”)

A style of a DoS attack, the “distributed denial of service” refers to attacks coming from multiple computers. (Generally, this refers to a fairly large number of computers.) Attackers in possession of botnets of zombie computers may often launch a coordinated attack. If there is a greater amount of resources (such as network bandwidth, or perhaps computational processing power) by the attacking machines, they may be able to overwhelm the resources of the attacked machine.

See also: DRDoS.

[#drefldos]: Distributed Reflected DoS (“DRDoS”)

A variation of DDoS is to use “distributed reflected DoS” (“DRDoS”), where the attacker uses a distributed attack to contact various computers on the Internet. For example, the attacker may have a dozen machines each contact a dozen different web servers with a TCP SYN connection (meaning that the connection has the “synchronize” flag bit is set to a value of one). Since all legitimate HTTP traffic starts with a TCP SYN packet, the web servers respond with a TCP SYN-ACK response. However, the compromised computer that sent the TCP SYN packet used a false “source” address. The Internet routers don't suspect that the “source” address is fake, because this practice looks identical to what happens whenever packets get forwarded.

The result of a DRDoS is that web servers send the TCP SYN-ACK packets to the targeted victim. Furthermore, since the trageted victim did not actually initiate the TCP SYN, the connection will fail. This often results in the web servers believing that the connection is failing, so the web servers retry by sending a duplicate TCP SYN-ACK packet. If the victim checks Internet traffic logs, all of the logs appear to come from legitimate web servers at organizations that are likely to be performing legitimate actions. Therefore, the attacker gets a multiplicative effect in attacking, and another hop of difficulty in tracing an attack's actual origins.

Just as DoS should have a lowercase o to avoid ambiguity from the operating systems called “Disk Operating System”, DRDoS should have the lowercase o to avoid ambiguity from Digital Research's DOS product, DRDOS.

[#de9]: DE9

The phrase is often written both with and without a hyphen: e.g. DE-9 or DE9.

One of the D-sub ports. A DE-9P/M (DE-9 plug/male) port on a computer is typically a serial port. (One common use for such a port on computers which were not compatible with an IBM PC was to be used as a port for a gaming joystick on an Apple 2.) A DE-9S/F (DE-9 socket/female) port on a computer may be a pre-VGA video port: Hercules, CGA, MDA, and EGA. Also, many early computers and video game systems which were not IBM PC compatible used these as joysticks, including the Atari systems (both the 2600 and computer systems), Commodore and Amiga systems, and the Sega Master System. Although the plugs fit, these joysticks were not necessarily compatible on an electrical level, although some joysticks may have had a switch to allow compatibility on multiple platforms.

A slightly odd thing is that the DB-25 serial ports have the male end on the computer, while DE-9 serial ports have the male end on the computer. (Computers may also have DB-25S/F ports and DE9P/M ports, but neither of these are serial ports.) So to determine whether a serial port has the male or female end on a computer will depend on the size of the shell, whether it is DB-25 or DE9.

These are 9-pin variations of D-subminature, and technicians were familiar with DB-25 ports. These DE-9 ports have often been referred to by the terms DB-9 and DB9, not only by technicians but also as part of official product documentation/specifications. This was so prevelent that references to the term “DB-9” are more likely to be the DE-9 standard, using the DE shell size, rather than to actually be using a DB shell size like what a DB-25 does. Also, most technicians have been indoctrinated to calling these DE-9 ports by the name DB-9, although DE-9 is really the more proper and sensible term.

This type of port often used the RS-232 signaling standard.

[#de15]: DE-15 (“DE15”)

The phrase is often written both with and without a hyphen: e.g. DE-15 or DE15.

Used for VGA connectors, as well as many newer connectors which are essentially compatible with VGA and with each other, such as SVGA and XGA connectors. The computer has DE-15S/DE-15F (DE-15 socket/female), while the monitor has DE-15P/DE-15M (DE-15 plug/male). The monitor may have a plug with a DE-15P/DE-15M connector at the end, or the monitor may simply have a DE-15P/DE-15M port which will require the uses of a plug that has DE-15P/DE-15M on one end and DE-15S/DE-15F on the other end.

[#decibel]: decibel

The term “dB” is an abbreviation for decibel. A decibel is, quite simply, an amount of bels (ten bels, or a tenth of a bel?). The term “decibel” is more well known as being a measurement of sound. On a broader scale, decibel has to do with the energy/strength of waves, including the radition in airwaves used by Wi-Fi. So, DB loss can involve a loss of signal strength (typically for wireless communications).

A bel is a relative term, similar to the word “half” Just as a signal can lose half of its strength, a signal can lose some bels (or dBs). Like the word “half”, a loss in decibels does not refer to a specific measurement that can, by itself, by meaningfully compared. Instead, the term really only has meaning when compared to another number/value.

[#decremnt]: decrement

Subtracting one. So, decrementing the number 16 results in 15. The opposing action is called “increment”.


This is an action that some organizations take to officially classify a technology or practice as being discouraged for all future deployments (instances were someone is actually implementing the technology/practice), because the organization instead favors using a specific newer technology (or “method of implementation”) instead of using the specific older one. Only an organization that is generally recognized for leading any future development of the standard is likely to be viewed as having any authorization to& ldquo;deprecate”.

As an example, IEEE Tutorial: Use of Extended Unique Identifier (“EUI”) and similar, archived in July 2010 by the Wayback Machine @ Archive.org identifies a standard called “EUI-60” as being deprecated, and notes, “The term deprecated does not imply a demise of [the specific technology being discussed], but implies the [newer technology] (as opposed to [the older technology]) [...] should be used in future applications.” (Quoted text replaced with bracketed terms, in order to genericize the conversation.)

Note that just because a technology is “deprecated” does not mean that it can be meaningfully used. Sometimes an older technology may have some advantaged, such as widespread compatability and ease-of-implementation. However, people who do cling to the older deprecated methods may find more of a struggle if they also wish to try to adopt some of the newer feature where the technology is moving towards.

[#dscractl]: Descretionary Access Control (possibly abbreviated “DAC”, although that abbreviation may have other, more common expansions)
[#digsubln]: Digital Subscriber Line (“DSL”)

A service, provided by a telephone company, which provides Internet access. A real, full, standard DSL connection should be faster than many older alternatives, including dial-up over POTS, ISDN, or T1 lines.

[#din]: DIN

Not to be confused with the similar Mini-DIN, this refers to a connector with metal shielding that is mostly circular, forming a circle of 13.2 millimeters in diameter. However, there is a notch in the circle to help with orientation. There are also pins in a standard layout. For computers, the most common DIN connector was the type used by older keyboards that used the DIN 41529 5/180° connector. Memorizing DIN 41529 5/180° is overkill: simply knowing that this was called a “DIN connector” is generally much more expertese than commonly needed: even knowing that this was the older, bigger style of connections used for keyboards is above average technical knowledge. The term DIN stands for Deutsches Institut für Normung, a German organization.

This stopped being used as the newer PS/2 connector became more popular. (The PS/2 connector since became less popular than simply using USB, a standard which did not exist when PS/2 connectors became popular.)

[#drcatcst]: direct attached storage

A device which is attached to the host computer using a direct connection, not requiring the use of a network (including network infrastructure such as a switch). The term may apply to drives in a host. (Whether or not that is a correct usage of the term, the term has been known to be used in that fashion.) Other examples would be USB drives, or any drive that has a data cable going directly to the computer.

Similar technologies may include NAS, SAN.

[#dns]: DNS (Domain Name SystemDomain Name System)
RFC 1034 section 1 refers to “the Domain Name System (DNS)”. (Later on, the RFC 1034 section 2.4 : Elements of the DNS refers to “The DOMAIN NAME SPACE” as being part of one of the “three major components” of DNS. That term uses the initials of “DNS” as well, but the proper usual expansion of the term “DNS” is Domain Name System.
[#domain]: domain
In the IT field

A group of computers, devices, and/or address names which are all authorized to be using a common portion of a name, or, alternatively, the term “domain” may refer to the actual common portion of a name that is used by such a group. For example, a domain name such as delorie.com may have subdomains of “www.delorie.com.” and ftp.delorie.com and chess.delorie.com. All of these addresses use the common portion of “delorie.com” (potentially followed by an optional period) at the end of their name, and so all of these addresses (www.delorie.com, ftp.delorie.com, chess.delorie.com, and even the name delorie.com itself) are all part of a single domain which is delorie.com.

Certain sites may have a domain within a domain, such as a domain called internal.example.com which would entirely exist within the domain of example.com (because anything that ends with internal.example.com would also end with example.com). The terminology for this is to call the inner-more domain a “subdomain” of the outer domain. On the Internet, a domains released by ICANN is called a TLD, which stands for top-level domain.

The pattern of separating subdomains from domains by using periods is part of the most common notation of the specific naming scheme used by the Internet standard called “Domain Name System” (“DNS”). Other naming methods, such as LDAP, may also use domains which may also have patterns that exist in all names that are part of a specific domain or subdomain.

The two most common naming schemes which use the term “domain” for such groups of names and/or devices using those names are the naming scheme of the Internet's “domain name system” (“DNS”) and the names of “Active Directory” domains.

In the math field

The domain of a function is the collection of all possible/valid/accepted input values. For example, a function that returns the square root of a positive simple number (a.k.a. not a complex number involving a non-zero value for the “imaginary number” commonly referred to as “i”) has a domain which is the group of all positive numbers. Numbers which are not part of the domain are not allowed to be used as input for the function.

In contrast, a “range” refers to all possible output values. For example, if a function accepts integers and returns the result of squaring the input, then the range is going to be all non-negative numbers where the final digit is an even number. English speakers trying to remember the different terms “domain” and “range” may remember that the word domain ends with “in” and is the term that refers to input.

In the field of computer programming
Like the definition of a functional (a.k.a. function-related) “domain” in mathematics, the domain of a function in computer programming refers to the possible values that are accepted by the function as input. Using an example of a square root function for simple numbers (a.k.a. non-complex numbers which do not involve non-zero values for the “imaginary” portion of the number), the domain may be all positive numbers. If a negative number is provided to such a function, the input is not in the domain and the function may return a value and/or error message which indicates that the input was not valid (because the input was not part of the domain).
[#dos]: DOS, DoS
DOS: Disk Operating System

This is a name that was used by several operating systems, and a phrase that was used as part of the name of other operating systems. These include MS-DOS and several largely compatible operating systems including FreeDOS, DR-DOS, OpenDOS, PC-DOS, and PTS-DOS. Also, Apple had released a version that they called of DOS, as well as ProDOS. (Apple's offerings were unrelated to the MS-DOS compatible offerings.)

[#denyofsv]: DoS: Denial of Service

Note: The abbreviation (see the letters “dos” as an abbreviation) should include a lowercase “o” to distinguish the abbrevation from DOS, which has a different meaning (“Disk Operating System”). This basically refers to any sort of attack (or action which accidentally) causes a service to become unavailable. The service is (whether intentionally or unintentionally) denied. (The term might, however, not be appropriate for intentional and authorized actions such as scheduled downtime.)

A commonly referred to variation is DDoS.

[#dpi]: DPI
Dots per inch

Perhaps most commonly referring to the amount of resolution of ink dots on a piece of paper (or similar, such as if an image was printed onto a T-Shirt or a sign is printed onto a large wooden board), this could also refer to things like the dot pitch (number of pixels per inch) of a monitor.

Deep packet inspection

A term used when a device (probably most often a firewall) looks at inner payloads of traffic.

Traffic inspection is routine and required for normal communications to occur, although routing can typically be done by looking at:

  • protocol numbers (e.g.: Ethernet protocol identifies IPv6 or IPv4
  • host addresses (Layer 3, IPv6 addresses or IPv4 addresses)
  • port numbers (for a protocol implementing Layer 4 of the OSI Model, such as TCP or UDP). These may be used for firewalling actions, including redirecting traffic (using port-based forwarding, a.k.a. port forwarding)

Instead of just looking at the type of information identified by the above bullet points, a device performing “deep packet inspection” may scan information in the payload of TCP segment (or a UDP datagram).

A commonly considered example is a firewall that generally allows HTTP traffic using the standard default port 80, but attempts to block certain types of content. The decision to block may be based on an implementation of some sort of content filtering technology, or some other traffic analysis (like frequency, and not just content?).

If the term “deep protocol inspection” is used, that likely refers to the same concept: that refers to the same thing as “deep packet inspection” (and may be abbreviated the same way: DPI).

[#domcntlr]: Domain Controller (“DC”)
A computer which is essentially in charge of an Active Directory domain. The domain controller typically fulfills authentication requests for the domain, and may also share information such as group policies. To fulfill these roles, the domain controller has information about user accounts. Often, the domain controller will also have additional roles such as being a file server for the users (which may make a lot of sense because the system already has information about the users), and possibly other critical infrastructure such as being a name resolution server and an automatic addressing server (which may make a lot of sense, in part because those services should be reliable and the domain controller may be a more expensive system and so should be able to provide reliability).
[#download]: download

Very much like the word “transfer”, the terms “upload” and “download” can be used as a verb (saying that something is happening), or as a noun (referring to a specific instance when the action occurs). The word “transfer” is an excellent word to use as a comparison to the words “upload” and “download”, because uploads and downloads are transfers.

The terms “upload” and “download” have been used differently by some different people. With both ways of using these terms, the terms refer to copying data from one computer (or device) to another. In both ways of using the term, one device sends the data, and one device receives the data.

Some organizations have used the term “download” to refer to a larger and more centralized computer sending information to a smaller and less centralized computer. Determining which computer is more “powerful” is not necessarily a strict measurement, and may be based on generalizations such as assuming that centralized computers, like servers, interact with other computers used by multiple users, and so those centralized computers are more powerful (in theory). So, a web server would generally be considered to be more centralized and powerful than the equipment used for running the web browser.

Which computer is the more powerful “server” is one way to determine whether a transfer is considered to be an upload or a download. With this definition, a computer may “download” data to another computer by sending a file. For example, when a user is obtaining data from a web server, the user is downloading the data, and the web server is also downloading the data. Both devices are being involved with transfering data that goes from the web server to the client, so the term “download” is used.

Another way that these terms have been used is that downloading refers to receiving, and uploading refers to sending. This is typically how the terms have been used by some software, such as specialized software implementing a file transfer protocol. Using this definition, the web client downloads data, and so the other end must be uploading the data. Therefore, the web server is uploading data, according to this definition. With this definition, nobody ever “downloads data to” anything, they “download data from” somewhere and “upload data to” somewhere.

Lots of computer experts who watched some of the various “Star Trek” shows on television have been known to be bothered by the television show's usage of the term “download”, because the term was used in a way that described data moving in an opposite direction of what they felt that a “download” would do. The reason for this was simple: there are multiple definitions of the word “download”, and the authors of the television show were using the term different than what people would use when they sent a file to a friend.

[#dpms]: DPMS
Display Power Management Signaling

A method of power saving related to video output displays.

DOS Protected Mode Services

Perhaps most famously implemented by EMM386 in at least some versions of operating systems based on DR-DOS code? (If details are available, try seeing the section on DOS Memory.)

[#dslabbr]: DSL

Probably: Digital Subscriber Line.

Also, the acronym of an operating system that uses the kernel. The name of this operating system (“D@#& Small Linux”) contains inappropriately sacreligiously profanity, and so is not discussed in great detail.

[#dsub]: D-subminiature (“D-sub”)
The DA-15 may be used for a “game port”: MIDI ports may also use DA-15 (although some MIDI ports have also used DIN connectors). DE-9 connectors are part of the family of D-subminiature (or “D-sub”) connectors which include DA-15, DB-25, DC-37, DD-50, and DE-9. DE-9 is often referred to as DB-9.
[#duid]: DUID
DHCPv6 UID, BSDlabel Disk UID
[#duotrigi]: duotrigint

This word is basically made up of two parts: duo, and trigint. It refers to a group of two plus thirty (thirty two).

This part of the phrase “dotted duotrigint” was discovered looking for a phrase to describe the notation used with IPv6 Reverse DNS. The goal was to find a phrase/term derived from the pattern used in the much more common term “dotted quad”, which refers to the standard notation of writing IPv4 addresses.

(Finding the prefix “duotrigint” took a bit of work, using the obversation on prefixes from Mazes.com's Numbering Systems and Place Values (archived by the Wayback Machine @ Archive.org), a page that along with hubpages.com page on Green and Latin Prefixes (archived by the Wayback Machine @ Archive.org) seemed to back up the (then-tentatively) selected prefix determined from the options of logical choices seen on “Math Forum”'s “Ask Dr. Math”'s page on “Prefixes in Math” page.)

[#dvi]: DVI

A type of video connector...