D

DACL: See discretionary access-control list.
DBCS: See double-byte character set.
DC: See device context.
DDE: See dynamic data exchange.
DDE client application: An application that requests a conversation with a dynamic data exchange (DDE) server application, and receives data from the server during the conversation. See also DDE server application.
DDE conversation: The interaction between a dynamic data exchange (DDE) client and a DDE server application.
DDE server application: An application that provides data to a dynamic data exchange (DDE) client application during a DDE conversation. See also DDE client application, DDE conversation.
DDE transaction: An exchange of messages or data between a dynamic data exchange (DDE) client application and a DDE server application. See also DDE client application.
dead key: A key used with another key to create an accented character. A dead key, when pressed, produces no visible character but indicates that the accent mark it represents is to be combined with the character produced by the next letter key pressed. See also key.
deadlock: A bug where the execution of thread A is blocked indefinitely waiting for thread B to perform some action, while thread B is blocked waiting for thread A. For example, two threads on opposite ends of a named pipe can become deadlocked if each thread waits to read data written by the other thread. A single thread can also deadlock itself. See also named pipe, thread.
debugger: An application that enables a developer to observe and correct programming errors by stepping through an application program, examining data, and checking conditions.
debugging: The process of observing and correcting logical and syntactical errors in an application.
debugging event: An event that occurs in a process being debugged that causes the kernel to notify the debugger. Also, the notification the kernel sends to the debugger. See also debugger, process.
default color palette: An array of RGB values identifying the colors that can be used with a device context by default. Windows associates the default color palette with a context whenever an application creates a context for a device that supports color palettes. The default color palette ensures that colors are available for use by an application without requiring additional action by the application.
default window procedure: A system-defined function that provides default processing for messages an application-defined window procedure does not process. See also window procedure.
desktop wallpaper: The pattern created by the bitmap that the desktop window uses to paint the background of the screen.
desktop window: A system-defined window that paints the background of the screen and serves as the base for all windows displayed by all Windows applications.
detached process: A console process that does not have access to the console of its parent process. Typically, a detached process runs in the background, but it can use the AllocConsole function to create a new console if it needs to print a message to the screen or get input from the user. See also console process, parent process.
device: Input sources and output destinations are collectively referred to as devices. Some examples of devices are keyboard (input), monitor (output), printer(output), and disk files, which are input and output devices.
device capabilities: The curve-, line-, polygon-, raster-, and text-drawing capabilities of a display or printer.
device context: Structure that defines a set of graphic objects and their attributes, and the graphic modes that affect output. In addition, the device context (DC) refers to a physical output device—its name, device driver, and other attributes. GDI function call parameters contain a handle to a DC to include the attributes of the specified device. There are four types of DC: display (supports drawing operations on a video display terminal), printer (supports drawing operations on a printer or plotter), memory (supports drawing operations on a bitmap), and information (supports retrieval of device data.) See also graphic modes, graphic objects.
device coordinate space: One of four coordinate spaces used for all graphic device interface (GDI) drawing operations.
device-dependent bitmap: An array of bits that can only be used with a particular display or printer.
device element: Data required for operation of Media Control Interface (MCI) compound devices. The device element is generally an input or output data file.
device-independent bitmap (DIB): An array of bits combined with several structures that specify the width and height of the bitmapped image (in pixels), the color format of the device where the image was created, and the resolution of the device used to create that image. See also bitmapped image, pixel.
device type: A class of Media Control Interface (MCI) devices that respond to a common set of commands.
Dfs: See Distributed File System.
DIB palette: The logical color palette created when a device-independent bitmap (DIB) was created. See also color palette.
DIB pattern-brush: A logical brush created from a device-independent bitmap (DIB). See also device-independent bitmap (DIB), logical brush.
digital differential analyzer (DDA): An algorithm that determines which pixels on a video display (or dots on a printed page) are part of a line or curve. See also pixel.
directory: An organizational construct supported by most disk-based operating systems. Rather than listing all the files on a volume at once, users can create multiple directories to contain groups of files. Directories can also contain other directories.
disabled window: A window that cannot receive input from keyboard, mouse, or other input device.
discretionary access-control list (DACL): An access-control list that is controlled by the owner of an object and that specifies the access particular users or groups can have to the object. See also access-control list (ACL), system access-control list.
disk drive: A physical device that reads from or writes to disks. Disk drives are referenced by letters, typically A for the first floppy-disk drive, B for the second floppy-disk, C for the first fixed-disk drive, D for the second fixed-disk drive, and so on. Each drive on an operating system is assigned a unique letter to distinguish it from other drives.
display context: A special device context that treats each window like a separate screen surface. See also device context, window.
display driver: A Windows dynamic-link library (DLL) that contains functions that process input from the graphics engine and convert that input into device-specific commands. These commands are processed by the display adapter. See also dynamic-link library (DLL).
display element: The parts of a window and the Windows display that appear on the system display screen.
Distributed File System (Dfs): Windows NT system software that provides distributed file system capabilities on computers running Windows NT Server 4.0 and later, Windows NT Workstation, and Windows 95. Dfs organizes shared resources on a network in a tree structure, and it provides the ability to logically group shares on multiple servers. See also junction point, leaf volume, root volume, alternate path.
dithering: A graphics technique that simulates a color by altering two or more colors in a pattern.
division type: The technique used to represent the time between Musical Instruments Digital Interface (MIDI) events in a MIDI sequencer.
DLL: See dynamic-link library (DLL).
domain: A group of workstations and servers that share a single group name.
double-byte character set (DBCS): A mapping of characters to their identifying numeric values, in which each value is 2 bytes wide. Double-byte character sets are sometimes used for languages that have more than 256 characters. For example, a double-byte character set is used to encode Japanese (Kanji) characters. See also multibyte character set.
double-click: To press and release a mouse button twice in quick succession.
drag: To move the mouse while holding down a mouse button.
drag-drop: To select one or more files in File Manager, drag them to an open application, and drop them there.
driver service: A service that follows the device driver protocols for Windows NT rather than using the Service Control Manager interface.
drop-down combo box: A combo box, created by using the CBS_DROPDOWN style, containing a drop-down list and a selection field that can be edited by the user.
drop-down list: A list in a combo box that is visible only when it is opened by the user. Combo boxes with the CBS_DROPDOWN and CBS_DROPDOWNLIST styles contain drop-down lists.
drop-down list box: A combo box, created by using the CBS_DROPDOWNLIST style, containing a drop-down list and a selection field that cannot be edited by the user. A drop-down list box can be used in place of a list box when screen space is tight.
due time: The time at which the state of the waitable timer is to be set to signaled. This value is specified when the timer is started. A positive value indicates an absolute time. A negative value indicates a relative time.
dynamic data exchange (DDE): A form of interprocess communications that uses shared memory to exchange data between applications. Applications can use DDE for one-time data transfers and for ongoing exchanges in applications that send updates to one another as new data becomes available.
dynamic-link library (DLL): A .DLL file that contains one or more functions compiled, linked, and stored separately from the processes that use them. The operating system maps the DLLs into the process's address space when the process is starting up or while it is running. The process then executes functions in the DLL. See also process.
dynamic priority: A thread priority value used by the scheduler in making scheduling decisions. The value for each thread can never be lower than the thread's base priority, but it can be raised and then lowered to enhance responsiveness to input or other significant events. See also base priority, thread.