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V

V.25ter
V.25 is the ITU-T standard for Serial Asynchronous Automatic Dialing and Control, commonly known as the "AT" command set.
V.4
V.4 is an ITU-T standard for the general structure of signals over the public telephone network. The V.4 standard governs the data transmission of signals created from international alphabet number 5 code.
valid page
A virtual page that is currently in physical memory.

See also invalid page.

value entry
A named value with assigned data within a registry key.

See also registry and key object.

VBN
Virtual block number. A virtual block number identifies a block (in other words, "sector") relative to the start of a file. For a file with N blocks of data, the corresponding VBNs are numbered 1 through N.
VCACHE
In Windows, a 32-bit protected-mode cache driver.
VCB
Volume control block. An internal file system structure in which a file system maintains state about a mounted volume.
VCOMM
In Windows, a 32-bit protected-mode communications driver.
VCR
Video cassette recorder. An analog magnetic recording and playback machine. Usually used for recording and viewing full-motion video; also useful as a data backup device.
VDM
Virtual DOS machine. A protected subsystem that emulates MS-DOS and DOS-based Windows.
vertical blanking interval (VBI)
The length of time required to move a graphics display's electron beam from the bottom scan line back up to the top scan line.
VGA
Video graphics array. A video adapter that supports 640x480-pixels color resolution. Video display standard for boot devices under Windows operating systems. Provides medium-resolution text and graphics.
video codecs
Full-color video. Requires 3 bytes per pixel, at 640x480 resolution; equals nearly 1 MB of digital data per frame. This means that a developer could easily use 1 GB of hard-disk space by storing less than one minute of uncompressed digital video information.
Video Electronics Standards Association (VESA)
An organization that sets standards for video devices.
video port extensions (VPE)
The video port extensions to DirectX®. Driver developers for devices with a hardware video port should implement these extensions. The hardware video port is a dedicated connection between video devices, typically between an MPEG device or NTSC decoder and the video card. This dedicated connection carries horizontal sync (Hsync) and vertical sync (Vsync) information with the video data. The hardware video port and overlay can use this sync information to flip automatically between multiple buffers, writing to one surface while the overlay displays another. This allows tear-free video without burdening the application.
video request packet (VRP)
A mechanism used to communicate device I/O control requests from a display driver to its corresponding adapter-specific miniport driver. For example, when a display driver calls EngDeviceIoControl, this function calls a system service causing the NT-based operating system I/O Manager to set up an IRP and call the Microsoft-supplied video port driver with that IRP. The video port driver uses the IRP to set up a VRP in a VIDEO_REQUEST_PACKET structure. The video port driver then calls the corresponding video miniport driver's StartIo entry point with the VRP.
VideoPort routines
An interface to adapter-specific miniport drivers exported by the system-supplied video port driver. Video miniport drivers call these routines to obtain all system support they need to carry out I/O operations.
view
A whole or partial mapping of a section object in the virtual address space of a process. For more information, see Section Objects and Views.
virtual device driver (VDD)
A device driver that operates in user mode and communicates with a corresponding device driver in kernel mode. A VDD supports only special-purpose hardware devices from an MS–DOS application. The VDD acts as a layer between MS-DOS applications and the hardware attached to the machine running an NT-based operating system.

For more information see the topic, Virtual Device Drivers for MS-DOS Applications or Special Hardware.

virtual DOS machine (VDM)
See Windows NT virtual DOS machine and NTVDM.
virtual memory
A view of memory that does not necessarily correspond to the underlying physical memory structure. For example, a given range of virtual addresses might be mapped to and backed by some number of discontiguous physical pages, even though the corresponding virtual pages can be accessed as a single, contiguous range.
VM
Virtual machine. Software that mimics the performance of a hardware device. For example, a software program that allows applications written for an Intel processor to be run on a Motorola chip interprets the Intel machine instructions, becoming a virtual Intel machine.
VMCB
Volume map control block. An opaque structure that stores VBN-to-LBN mappings for an IFS’s volume file.
VMR
Video Mixer-Renderer. A DirectShow sink filter that displays the contents of a video stream.
volume
Volume is the general term that refers to all of the following entities that you can create and use on a computer running Windows:

A volume has a single drive letter assigned to it, and is formatted for use by a file system.

volume file
A virtual file, maintained by certain file systems, whose contents map metadata structures of the on-disk file system. A volume file is a type of stream file.
VPB
Volume parameter block. A VPB is a structure, defined by the I/O Manager, that maps a file system’s volume device object to the device or partition upon which the volume is mounted. The file system's device object is actually used to represent the volume (VPB) mounted on the actual device (physical device object). Device objects for physical disks, tapes, CD ROMs, and RAM disks have associated VPBs.

See also mount.

VRP
Video request packet. A structure used to communicate device I/O control requests from a display driver to its corresponding adapter-specific miniport driver. For example, when a display driver calls EngDeviceIoControl, this function calls a system service and the I/O Manager sets up an IRP and calls the system-supplied video port driver with that IRP. The video port driver uses the IRP to set up a VRP and calls the corresponding video miniport driver’s StartIo entry point with the VRP.
VxD
Virtual device driver. A device driver that runs at the privileged ring 0 protected mode of the microprocessor. Can extend the services of the Windows kernel, supervise hardware operations, or perform both functions. Such driver files are usually named according to the scheme VxD, where x refers to the device or service supported.
Built on Friday, April 11, 2003