Computer Terms Beginning with "D"

[MysteRy]

Domain Suffix

Example: "The most popular domain suffix is '.com.'"

A domain suffix is the last part of a domain name. Common examples include ".com," ".net," and ".org," though many others exist. For example, country-specific domain suffixes such as ".uk," and ".se", and ".jp" can be used to identify websites located in the United Kingdom, Sweden, and Japan.

Newer domain suffixes, such as ".tv" and ".mobi" are used to identify specific types of websites. For example, the ".tv" domain suffix is commonly used by television station websites. The ".mobi" suffix is used for mobile versions of websites that can easily be viewed on mobile devices. Domain suffixes are also called "top-level domains" or "TLDs." You can view a comprehensive list of TLDs at the Sharpened.net Domain Suffixes page.

GoDaddy allows you to choose one of several different domain suffixes when you register a domain name.

[MysteRy]

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.

[MysteRy]

DOS

Stands for "Disk Operating System." DOS was the first operating system used by IBM-compatible computers. It was originally available in two versions that were essentially the same, but marketed under two different names. "PC-DOS" was the version developed by IBM and sold to the first IBM-compatible manufacturers. "MS-DOS" was the version that Microsoft bought the rights to, and was bundled with the first versions of Windows.

DOS uses a command line, or text-based interface, that allows the user to type commands. By typing simple instructions such as pwd (print working directory) and cd (change directory), the user can browse the files on the hard drive, open files, and run programs. While the commands are simple to type, the user must know the basic commands in order to use DOS effectively (similar to Unix). This made the operating system difficult for novices to use, which is why Microsoft later bundled the graphic-based Windows operating system with DOS.

The first versions of Windows (through Windows 95) actually ran on top of the DOS operating system. This is why so many DOS-related files (such as .INI, .DLL, and .COM files) are still used by Windows. However, the Windows operating system was rewritten for Windows NT (New Technology), which enabled Windows to run on its own, without using DOS. Later versions of Windows, such as Windows 2000, XP, and Vista, also do not require DOS.

DOS is still included with Windows, but is run from the Windows operating system instead of the other way around. The DOS command prompt can be opened in Windows by selecting "Run..." from the Start Menu and typing cmd.

[MysteRy]

Dot Matrix

A dot matrix is a 2D matrix of dots that can represent images, symbols, or characters. They are used for electronic displays, such as computer monitors and LED screens, as well as printed output.

In a dot matrix display, the images are estimated using a discrete set of dots instead of lines and shapes. Therefore, the more dots that are used, the more clear and accurate the image representation will be. For example, a 16x16 dot matrix can represent the letter "S" more accurately than a 8x8 matrix. If enough dots are used, the image will appear as a contiguous display rather than a group of dots. This is because the human eye blends the dots together to create a coherent image. For example, newspaper print is made up of dot matrixes, but it is hard to notice unless you look very closely at the paper.

Bitmap images on a computer screen are also dot matrixes, since they are made up of a rectangular grid of pixels. If you look closely enough at your monitor, you may even be able to see the dots that make up the image. But be nice to your eyes and don't stare too long!

While "dot matrix" has a broad definition, it can also be used to describe a specific type of printer. Dot matrix printers, or "impact printers," were introduced in the 1970s. These printers typically use the kind of paper with small holes on each side that are used to feed the paper through the printer. They are called dot matrix printers because they use a matrix of dots to print each character. While they do not have a very high resolution, dot matrix printers are an effective way of printing basic text documents. Therefore, while most businesses now use inkjet or laser printers, some organizations still find dot matrix printers to be an efficient printing solution.

[MysteRy]

Dot Pitch

This is the measurement used to determine how sharp the display of a CRT (Cathode Ray Tube) monitor is. It is measured in millimeters and the smaller the number, the finer the picture. Most CRT monitors will have a dot pitch between 0.25 and 0.28. However, some large presentation monitors have dot pitches from 0.30 to 0.50 (which would make for really fuzzy images on a standard 17" desktop monitor). The difference between a "dot" (as in dot pitch) and a pixel is that a pixel is mapped onto the dots on the screen. When the monitor is set to lower resolutions, one pixel encompasses multiple dots. So pixels are typically larger than the "dots" on the actual screen.

In a CRT display with a shadow mask, the dot pitch is measured as the distance between the holes of the shadow mask, again in millimeters. "So what's a shadow mask?" you ask. It's basically a metal screen full of holes where three electron beams (red, green, and blue) pass through. These beams focus to a single point on the tube's phosphor surface. Thousands of these points make up the images on your screen. Neat, huh? In a CRT display that uses an aperture grill (like a Sony Trinitron monitor), the dot pitch is measured by the distance between adjacent slots where electron beams of the same color pass through.

[MysteRy]

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.

[MysteRy]

Download

This is the process in which data is sent to your computer. Whenever you receive information from the Internet, you are downloading it to your computer. For example, you might have to download an upgrade for your computer's operating system in order to play a new game (especially if you're using Windows). Or you might download a demo version of a program you are thinking about buying from the software company's Web site. The opposite of this process, sending information to another computer, is called uploading.

[MysteRy]

DPI

Stands for "Dots Per Inch." DPI is used to measure the resolution of an image both on screen and in print. As the name suggests, the DPI measures how many dots fit into a linear inch. Therefore, the higher the DPI, the more detail can be shown in an image.

It should be noted that DPI is not dots per square inch. Since a 600 dpi printer can print 600 dots both horizontally and vertically per inch, it actually prints 360,000 (600 x 600) dots per square inch.

Also, since most monitors have a native resolution of 72 or 96 pixels per inch, they cannot display a 300 dpi image in actual size. Instead, when viewed at 100%, the image will look much larger than the print version because the pixels on the screen take up more space than the dots on the paper.

[MysteRy]

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."

[MysteRy]

DRAM

Stands for "Dynamic Random Access Memory." DRAM is a type of RAM that stores each bit of data on a separate capacitor. This is an efficient way to store data in memory, because it requires less physical space to store the same amount of data than if it was stored statically. Therefore, a DRAM chip can hold more data than an SRAM (static RAM) chip of the same size can. However, the capacitors in DRAM need to constantly be refreshed to keep their charge, so DRAM requires more power than SRAM.

Still, because DRAM can hold more data than SRAM and because it is significantly less expensive to manufacture, DRAM is the most common type of memory found in personal computer systems. While there are many types of DRAM available, the most common type is synchronous DRAM SDRAM, which is a faster version of standard DRAM. This is the type of memory most computers use for their main system memory.

If you choose to upgrade your computer's SDRAM, check your machine's requirements to see if the memory modules must be installed in pairs. If so, you will need to replace two modules at once and they must be the same size (i.e. two 1GB SDRAM memory modules).

[MysteRy]

Driver

This term usually refers to the person behind the wheel of a moving car. In the computer world, however, a driver is a small file that helps the computer communicate with a certain hardware device. It contains information the computer needs to recognize and control the device. In Windows-based PCs, a driver is often packaged as a dynamic link library, or .dll file. In Macs, most hardware devices don't need drivers, but the ones that do usually come with a software driver in the form of a system extension, or .kext file.

[MysteRy]

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.

[MysteRy]

Drop Down Menu

Example: "Websites often have drop down menus at the top of each page to provide easy navigation."

A drop down menu is a horizontal menu that displays a list of options when one of the primary menu items is selected. These options typically "drop down" below the selected menu item. Drop down menus may be used within programs (like a standard menu bar), as well as websites. Website drop down menus are often used for navigational purposes and are typically created using dynamic HTML (DHTML). They can help streamline navigation since they provide one-click access to more pages than a static navigation bar allows.

[MysteRy]

DSL

Stands for "Digital Subscriber Line." It is medium for transferring data over regular phone lines and can be used to connect to the Internet. However, like a cable modem, a DSL circuit is much faster than a regular phone connection, even though the wires it uses are copper like a typical phone line.

An asymmetric DSL (ADSL) connection allows download speeds of up to about 1.5 megabits (not megabytes) per second, and upload speeds of 128 kilobits per second. That is why it is called ADSL and not just DSL (because of the asymmetric speeds). There is also a "Symmetric Digital Subscriber Line" (SDSL) which is similar to ADSL, but allows data transfer speeds of 384 Kilobits per second in both directions. Theoretically, this type of connection allows download speeds of up to 9 megabits per second and upload speeds of up to 640 kilobits per second. The difficult part in establishing an DSL circuit is that it must be configured to connect two specific locations, unlike a regular phone line or cable modem. DSL is often seen as the new, better alternative to the older ISDN standard.

[MysteRy]

DSLAM

Stands for "Digital Subscriber Line Access Multiplexer." A DSLAM is a device used by Internet Service Providers (ISPs) to route incoming DSL connections to the Internet. Since a "multiplexer" combines multiple signals into one, a DSLAM combines a group of subscribers' connections into one aggregate Internet connection.

For example, a DSL access multiplier may receive signals from all the DSL modems in a certain neighborhood and patch them through to the Internet backbone. The DSLAM processes each incoming connection and may limit the bandwidth of certain DSL lines. Most DSL service providers use multiple DSLAMs to help route incoming and outgoing traffic in the most efficient way possible.