What are the device drivers?
A device driver, or a software driver is a type of computer software, typically
developed to make the hardware in your computer work. Typically this constitutes
an interface for communicating with the device, through the specific computer
bus or communications subsystem that the hardware is connected to, providing
commands to and/or receiving data from the device, and on the other end, the
requisite interfaces to the operating system and software applications. Often
called a driver for short, it is a specialized hardware dependent computer
program which is also operating system specific that enables another program,
typically an operating system or applications software package or computer
program running under the operating system kernel, to interact transparently
with a hardware device, and usually provides the requisite interrupt handling
necessary for any necessary asynchronous time-dependent hardware interfacing
needs.
Device driver theory
The key design goal of device drivers is abstraction. Every model of hardware
(even within the same class of device) is different. Newer models also are
released by manufacturers that provide more reliable or better performance and
these newer models are often controlled differently.
Computers and their operating systems cannot be expected to know how to control
every device, both now and in the future. To solve this problem, operating
systems essentially dictate how every type of device should be controlled. The
function of the device driver is then to translate these OS mandated function
calls into device specific calls. In theory a new device, which is controlled
in a new manner, should function correctly if a suitable driver is available.
This new driver will ensure that the device appears to operate as usual from
the operating systems' point of view.
Depending on the specific computer architecture, drivers can be 8-bit, 16-bit,
32-bit, and more recently, 64-bit. This corresponds directly to the architecture
of the operating system for which those drivers were developed. For example, in
16-bit Windows 3.11, most drivers were 16-bits, while most drivers for
32-bit Windows XP are 32-bit. More recently, specific 64-bit Linux and Windows
versions have required hardware vendors to provide newer 64-bit drivers
for their devices.
Device driver development
Writing a device driver is considered a challenge in most cases, as it requires
an in-depth understanding of how a given platform functions, both at the
hardware and the software level. Because many device drivers execute in kernel
mode, software bugs often have much more damaging effects to the system.
This is in contrast to most types of user-level software running under modern
operating systems, which can be stopped without greatly affecting the rest
of the system. Even drivers executing in user mode can crash a system if the
device being controlled is erroneously programmed. These factors make it more
difficult and dangerous to diagnose problems.
All of this means that the engineers most likely to write device drivers come
from the companies that develop the hardware. This is because they have more
complete access to information about the design of their hardware than most
outsiders. Moreover, it was traditionally considered in the hardware
manufacturer's
interest to guarantee that their clients would be able to use their hardware in
an optimum way. However, in recent years non-vendors too have written numerous
device drivers, mainly for use under free operating systems. In such cases,
co-operation on behalf of the vendor is still important, however, as reverse
engineering is much more difficult with hardware than it is with software,
meaning it may take a long time to learn to operate hardware that has an unknown
interface.
In Windows, Microsoft is attempting to address the issues of system instability
by poorly written device drivers by creating a new framework for driver
development known as Windows Driver Foundation (WDF). This includes UMDF User
Mode Driver Framework that encourages development of certain types of drivers
- primarily those that implement a message-based protocol for communicating
with their devices - as user mode drivers. If such drivers malfunction they
will not cause system instability. The KMDF Kernel Mode Driver Framework 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.
Device driver applications
Because of the diversity of modern hardware and operating systems, many ways
exist in which drivers can be used. Drivers are used for interfacing with:
* Printers
* Video adapters
* Network cards
* Sound cards
* Local buses of various sorts - in particular, for bus mastering on modern
systems
* Low-bandwidth I/O buses of various sorts (for pointing devices such as mice,
keyboards, USB, etc.)
* computer storage devices such as hard disk, CD-ROM and floppy disk buses
(ATA, SATA, SCSI)
* Implementing support for different file systems
* Implementing support for image scanners and digital cameras
Choosing and installing the correct device drivers for given hardware is often
a key component of computer system configuration.
Virtual device drivers
A particular variant of device drivers are virtual device drivers. They are
used in virtualization environments, for example when an MS-DOS program is
run on a Microsoft Windows computer or when a guest operating system is run
inside e.g. VMware. Instead of enabling the guest operating system to dialog
with hardware, virtual device drivers take the opposite role and emulate a
piece of hardware, so that the guest operating system and its drivers running
inside a virtual machine can have the illusion of accessing real hardware.
Attempts by the guest operating system to access the hardware are routed to
the virtual device driver in the host operating system as e.g. function calls.
The virtual device driver can also send simulated processor-level events like
interrupts into the virtual machine.
inside a virtual machine can have the illusion of accessing real hardware.
Attempts by the guest operating system to access the hardware are routed to
the virtual device driver in the host operating system as e.g. function calls.
Enjoy
Rohan
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