Virtual Device Driver FAQ
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This article contains frequently asked questions on the topic Virtual Device Driver....

1.Define Virtual Device Driver ?

In certain Microsoft operating systems, a virtual device driver is a program that handles software interrupts from the operating system (rather than hardware interrupts) for each of the computer's main hardware.

2.What is Device Driver ?

In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device.

3.How the driver communicates with the devices ?

Through the computer bus.

4.What is virtual device ?

Also referred to as a virtual peripheral, a virtual device mimics a physical hardware device, essentially tricking the CPU into believing that a device exists when actually it doesn't. For example, fax software can act as a virtual printer.

5.Virtual device driver can be abbreviated as ?


6.In VxD, what x stands for ?

x is the placeholder for a device name such as virtual keyboard driver, virtual mouse driver and so on.

7.What is the Purpose of VxD ?

VxDs are designed to virtualize hardware devices but we can also treat VxDs like ring-0 DLLs.

8.Device drivers can be abstracted into physical layer.  How ?

Physical layers communicate with specific device instances.

9.What is the extension of virtual device driver ?


10.Device drivers can be abstracted into logical layer. How ?

Logical layers process data for a class of devices such as Ethernet ports or disk drives.

11.How to use device drivers in Linux Operating System ?

In Linux environments, programmers can build device drivers either as parts of the kernel or separately as loadable modules.

12.Makedev includes a list of the devices in Linux, which are they ?

ttyS (terminal), lp (parallel port), hd (disk), loop (loopback disk device), sound (these include mixer, sequencer, dsp, and audio).

13.What is the extension of loadable device drivers in Windows ?


14.What is the extension of loadable device drivers in Linux ?


15.What is the advantage of  loadable device drivers ?

The advantage of loadable device drivers is that they can be loaded only when necessary and then unloaded, thus saving kernel memory.

16.Which are factors are to be considered while writing device drivers?

Writing a device driver requires an in-depth understanding of how the hardware and the software of a given platform function.

17.Who writes device drivers ?

The task of writing drivers usually falls to software engineers who work for hardware-development companies.This is because they have better information than most outsiders about the design of their hardware.

18.What is LDD ?

logical device driver (LDD)

19.Who write LDD ?

LDD is written by the operating system vendor.

20.What is PDD ?

Physical device driver (PDD)

21.Who write PDD ?

By the device vendor.

22.What is WDF ?

Microsoft has attempted to reduce system instability due to poorly written device drivers by creating a new framework for driver development, called Windows Driver Foundation (WDF).

23.What is Kernel-Mode Driver Framework (KMDF) ?

The Kernel-Mode Driver Framework (KMDF) model continues to allow development of kernel-mode device drivers, but attempts to provide standard implementations of functions that are well known to cause problems, including cancellation of I/O operations, power management, and plug and play device support.

24.Apple has an open-source framework for developing drivers on Mac OS X, which one is that ?

I/O Kit.

25.What is DLL ?

Dynamic-link library (also written without the hyphen), or DLL, is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems. These libraries usually have the file extension DLL, OCX (for libraries containing ActiveX controls), or DRV (for legacy system drivers).

26.How VxD become dangerous ?

VxDs are the most powerful entities in the system. Since they can do anything to the system, they are also extremely dangerous. An ill-behaved VxD can crash the system. There is no safeguard against ill-behaved

27.What is ring3 dll ?

ring3.dll is a process from Eastman Kodak Company. It can be found in the location of %programfilescommon%kodakifscore ing3.ring3.dll is a potential security risk which can be modified maliciously by virus.ring3.dll virus should be disabled and removed if it was attacked and brought you ring3.dll error.

28.VxD specific to which OS ?

VxDs are specific to Windows 9x.

29.Which are the different types of VxD under Windows 95 ?

Static VxD and Dynamic VxD.

30.What is Static VxD ?

Static VxDs are those VxDs that are loaded during system bootup and stay loaded until the system shutdown. This type of VxD dates back from the days of Windows 3.x.

31.What is Dynamic VxD ?

Dynamic VxDs are available under Windows 9x only. Dynamic VxDs can be loaded/unloaded when needed. Most of them are VxDs that controls Plug and Play devices which are loaded by Configuration Manager and Input Output Supervisor. You can also load/unload dynamic VxDs from your win32 applications.

32.VMM stands for ?

Virtual Machine Manager.

33.Define VMM ?

Virtual Machine Manager (VMM) is the true operating system behind Windows 95. It erects and maintains the framework for managing virtual machines. It also provides many important services to other VxDs.

34.VxDs, including VMM, communicate with each other via three mechanisms. Which are they ?

Control Messages, Service APIs, and Callbacks.

35.What is control messege?

VMM sends system control messages to ALL loaded VxDs in the system when some interesting events occur. In this regards, control messages are like windows messages of the ring-3 Windows applications.There are about 50 or so system control messages. The reason that there are not many control messages is that there are often many VxDs loaded in the system and each of them gets a crack at every control message, if there are too many control messages, the system will grind to a halt.

36.What is device control procedure ?

Every VxD has a function that receives and deals with control messages called device control procedure.

37.What is Service APIs ?

A VxD, including VMM, usually exports a set of public functions that can be called by other VxDs. Those functions are called VxD services. The mechanism of calling those VxD services is quite different from that of ring-3 applications. Every VxD that exports VxD services MUST have a unique ID number. You can obtain such IDs from Microsoft.

38.What is API ?

An application programming interface (API) is a source code based specification intended to be used as an interface by software components to communicate with each other. An API may include specifications for routines, data structures, object classes, and variables.

39.What is Callbacks ?

callbacks or callback functions are functions in VxD that exist to be called by other VxDs.Callbacks are not public like services. They are private functions whose adresses the VxD gives to other VxDs in specific situations.

40.What is virtual machine ?

A virtual machine (VM) is a "completely isolated guest operating system installation within a normal host operating system". Modern virtual machines are implemented with either software emulation or hardware virtualization or (in most cases) both together.

41.What is hardware virtualisation ?

Computer hardware virtualization is the virtualization of computers or operating systems. It hides the physical characteristics of a computing platform from users, instead showing another abstract computing platform.

42.What is the fullform of VPN ?

Virtual Private Network.

43.Define VPN ?

A virtual private network (VPN) is a network that uses primarily public telecommunication infrastructure, such as the Internet, to provide remote offices or traveling users access to a central organizational network.

44.Give an example for virtual device driver ?

Daemon Tools

45.Give some names of open drivers ?

CUPS, SANE, Vidix, Direct Rendering Infrastructure etc.

46.What is VMWare ?

Its a virtualisation software for providing multiple OSs in a sytem.

47.What is disk image ?

A disk image is a single file or storage device containing the complete contents and structure representing a data storage medium or device, such as a hard drive, tape drive, floppy disk, optical disc, or USB flash drive.

48.What is Vitualbox ?

VirtualBox is a powerful x86 and AMD64/Intel64 virtualization product for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also
the only professional solution that is freely available as Open Source Software under the terms of the GNU General Public License (GPL) version 2.

49.What is the benefit of running device drivers in user mode ?

The primary benefit of running a driver in user mode is improved stability, since a poorly written user mode device driver cannot crash the system by overwriting kernel memory.

50.What is Xen ?

Xen is a virtual-machine monitor providing services that allow multiple computer operating systems to execute on the same computer hardware concurrently.

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