VxD is the

device driver In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and ot ...

model used in Microsoft Windows/386 2.x, the 386 enhanced mode of

Windows 3.x Windows 3.x means either of, or all of the following versions of Microsoft Windows: * Windows 3.0 * Windows 3.1x Windows 3.1 is a major release of Microsoft Windows. It was released to manufacturing on April 6, 1992, as a successor to Windo ...

Windows 9x Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced from 1995 to 2000, which were based on the Windows 95 kernel and its underlying foundation of MS-DOS, both of which were updated in subs ...

, and to some extent also by the

Novell DOS 7 DR-DOS (written as DR DOS, without a hyphen, in versions up to and including 6.0) is a disk operating system for IBM PC compatibles. Upon its introduction in 1988, it was the first DOS attempting to be compatible with IBM PC DOS and MS-D ...

OpenDOS 7.01 DR-DOS (written as DR DOS, without a hyphen, in versions up to and including 6.0) is a disk operating system for IBM PC compatibles. Upon its introduction in 1988, it was the first DOS attempting to be compatible with IBM PC DOS and MS-D ...

, and

DR-DOS 7.02 DR-DOS (written as DR DOS, without a hyphen, in versions up to and including 6.0) is a disk operating system for IBM PC compatibles. Upon its introduction in 1988, it was the first DOS attempting to be compatible with IBM PC DOS and MS-D ...

(and higher) multitasker (TASKMGR). VxDs have access to the

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...

of the

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learnin ...

and all running processes, as well as raw access to the hardware. Starting with

Windows 98 Windows 98 is a consumer-oriented operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. The second operating system in the 9x line, it is the successor to Windows 95, and was released to ...

Windows Driver Model In computing, the Windows Driver Model (WDM) also known at one point as the Win32 Driver Model is a framework for device drivers that was introduced with Windows 98 and Windows 2000 to replace VxD, which was used on older versions of Windows such a ...

was the recommended driver model to write drivers for, with the VxD driver model still being supported for backward compatibility, until

Windows Me Windows Millennium Edition, or Windows Me (marketed with the pronunciation of the pronoun "me"), is an operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. It is the successor to Windo ...

. __TOC__

Name and design

The name "VxD" is an abbreviation for "virtual xxx driver", where "xxx" is some class of hardware device. It derives from the fact that most drivers had filenames of the form vxxxd.386 in

. Some examples are vjoyd.386 (joystick) and vmm.386 (memory manager). VxDs under Windows 3.x usually have the

filename extension A filename extension, file name extension or file extension is a suffix to the name of a computer file (e.g., .txt, .docx, .md). The extension indicates a characteristic of the file contents or its intended use. A filename extension is typically d ...

.386, while those under Windows 9x have .vxd. VxDs written for Windows 3.x can be used under Windows 9x but not vice versa.

History

Prior to the advent of Windows,

DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicatio ...

applications would either communicate directly with the various pieces of hardware (responding to interrupts, reading and writing device memory etc.) or go through a DOS

. As DOS was not multitasking, each application would have exclusive and complete control over the hardware while running. Though

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

applications don't often communicate directly with hardware, it was the only way for Windows drivers; and still is in the real and standard modes of Windows 3.x.

Windows/386 Windows 2.0 is a major release of Microsoft Windows, a family of Graphical user interface, graphical operating system, operating systems for Personal computer, personal computers developed by Microsoft. It was Released-to-manufacturing, release ...

and onward allowed multiple DOS applications to execute concurrently by executing each within its own

virtual machine In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardw ...

. To share physical resources among these virtual machines, Microsoft introduced virtual device drivers. These drivers solved issues relating to conflicting usage of physical resources by intercepting calls to the hardware. Instead of a machine port representing an actual device, it would represent a "virtual" device, which could be managed by the operating system.

Obsolescence

Although Windows 98 introduced the

(WDM), VxD device drivers can be used under Windows 98 and Windows Me. Using VxD drivers instead of WDM drivers in Windows 9x resulted in advanced

ACPI Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto c ...

states like

hibernation Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most ...

being unavailable. VxDs are not usable in

Windows NT Windows NT is a proprietary graphical operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems sc ...

or its descendants. Windows NT-based operating systems from 3.1 to 4.0 must use drivers written specifically for them, otherwise known as the

Windows NT Driver Model Windows NT is a Proprietary software, proprietary Graphical user interface, graphical operating system produced by Microsoft, the first version of which was released on July 27, 1993. It is a processor-independent, multiprocessing and multi-use ...

. Starting with

Windows 2000 Windows 2000 is a major release of the Windows NT operating system developed by Microsoft and oriented towards businesses. It was the direct successor to Windows NT 4.0, and was Software release life cycle#Release to manufacturing (RTM), releas ...

, Windows NT-based operating systems have adopted the Windows Driver Model from Windows 98. VxDs should not be confused with the similarly named

NTVDM Virtual DOS machines (VDM) refer to a technology that allows running 16-bit/32-bit DOS and 16-bit Windows programs when there is already another operating system running and controlling the hardware. Overview Virtual DOS machines can operate ei ...

-specific 'VDDs' (Virtual Device Drivers), which provide a method of emulating direct I/O under a Windows NT "DOS Box". NTVDM VDDs run as regular, 32-bit, user-mode DLLs, and must rely on the Win32 API (or another WDM driver) to emulate the desired I/O on behalf of the 16-bit program.

Name and design

History

Obsolescence

See also

References

Further reading