gamma ramp

A lookup table (LUT) of numeric values used to compensate for a particular monitor's color response. The table is divided into three parts (one each for red, green, and blue), with each part containing 256 lookup values.

A gamma ramp is used to map the range of possible intensities for each color to a limited number (256) of values. An IHV chooses these values so that the transition from one color intensity to the next is as smooth as possible, given that the eye perceives changes in light intensity nonlinearly.

Microsoft DirectDraw takes a pixel from the frame buffer, and examines it in terms of its individual red, green, and blue color components. Each component is represented by a value from 0 to 65535. DirectDraw takes the original value, and uses it as an index into a 256-element array (the ramp), where each element contains a value that replaces the original one. DirectDraw performs this "look-up and replace" process for each color component of each pixel within the frame buffer, thereby changing the final colors for all of the on-screen pixels.


See generic descriptor language (GDL).

generic printer description (GPD)

A text-based file used to describe a printer that is printing from Microsoft Windows using the Universal Printer Driver (Unidrv). A GPD contains information about the printer features that Unidrv presents in the user interface to allow the user to configure the printer.

A GPD also contains the printer commands and attributes that enable Unidrv to generate the correct printer-ready output data when the user prints from a Windows-based application. Creating a printer driver can be as simple as creating a GPD file if there is no custom functionality beyond what Unidrv provides.

generic descriptor language (GDL)

A mechanism for reading structured data, particularly data associated with printers. GDL files are used to configure Unidrv drivers and to configure bidi communication in Unidrv and Pscript drivers.


The actual shape (bit pattern, outline, and so forth) of a character image. For example, an italic letter 'a' (a) and a roman 'a' (a) are two different glyphs that represent the same underlying character. Synonymous with "character image" or simply "image."

glyph translation table (GTT)

A table that maps characters with the bitmaps that are used to display those characters.


See guest physical address (GPA).

gradient fill

A technique used to fill a rectangular or triangular region with color that changes smoothly across the region. For rectangular regions, the gradient fill can be specified as top to bottom, or left to right.

For more information, see the topic DrvGradientFill.

graphics capabilities bits (GCAPS)

A driver specifies its graphics capabilities by setting GCAPS_Xxx and GCAPS2_Xxx flags in the flGraphicsCaps and flGraphicsCaps2 members of the DEVINFO structure. GDI obtains the GCAPS when it calls the driver's DrvEnablePDEV routine.

graphics device interface (GDI)

Consists of Windows GDI and kernel-mode GDI. Windows GDI is a user-mode API used by applications that require graphics support. Kernel-mode GDI interfaces directly with kernel-mode graphics drivers, as well as Window Manager. Kernel-mode GDI exports several services and functions that can be called by device drivers to perform a host of drawing and graphics-related operations. This eliminates the need for graphics drivers to implement much of the required graphics functionality.

The Windows GDI library that is directly accessible to applications can be found in Gdi32.dll. It fields calls to the functions listed in and passes the application-supplied information to kernel-mode GDI by way of executive system services in the operating system. The kernel-mode GDI library is found in Win32k.sys. Kernel-mode GDI communicates with a graphics driver by calling the driver's implementations of the DDI functions listed in Winddi.h.

graphics engine

Another name for GDI.

See also the kernel-mode GDI definition under graphics device interface (GDI).

guest physical address (GPA)

A guest operating system's view of the physical memory in an SPA. There is one GPA per partition.

guest operating system

An operating system that is hosted by a partition, which uses hypercalls to access physical resources through the hypervisor.

guest virtual address (GVA)

A virtual address that enables address translation and provides a guest page table.


Globally unique identifier. A 16-byte quantity that is unique, having been generated from the unique identifier on a network card, the current date and time, and a sequence number. This combination of variables is used to allow any party to create identifiers that will be guaranteed not to match another GUID. For more information see the topic, Using GUIDs in Drivers.


See guest virtual address (GVA).



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