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A program that operates or controls a particular type of device that is attached to a computer.
Provides a s/w interface to hardware devices ,enabling operating systems and other computer programs to access hardware function without needing to know precise details of the hardware being used.
Its purpose is to allow smooth functioning of the hardware for which it is created and to allow it to be used with different operating systems.
Acts as a translator between hardware device and the programs using it

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A device driver converts general IO instructions into device specific operations

A device driver has three sides
1.One side talks to the rest of the kernel
2.One talks to the hardware end
2.One talks to the user

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Encapsulation
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Hides low level device protocol from the client.
Unification
Makes similar devices look the same
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Protection
Only authorized applications can use the device
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Multiplexing
Multiple applications can use the device concurrently

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 are the generic device drivers that load with the operating system into the memory as part of the operating system not the entire driver but a pointer to that effect so that the device driver can be invoked as soon as it is required.
The drivers are pertaining to BIOS, motherboard, processor, and similar hardware form part of Kernel Software.
A problem with Kernel Device Drivers is that when one of them is invoked, it is loaded into the RAM and cannot be moved to page file
(virtual memory). Thus, a number of device drivers running at the same time can slow down machines. That is why there is a minimum system requirement for each operating system. The different operating systems already add up the resources needed for kernel device drivers, so that end users need not worry about extra memory requirements.

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Usually triggered by users during their session on a computer.
It might be thought of devices that the user brought to the computer other than the kernel devices.
Drivers for most of the Plug and Play devices fall into this category.
User Device Drivers can be written to disk so that they don’t act tough on the resources.

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A driver communicate with the device through the computer bus or communication subsytems to which the hardware connects.
When a calling program invokes a routine in the driver,thedriver issues commands to the device
Once the device sends the data back to the driver,the driver may invoke routines in the original calling program

The different steps are:
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a device object is created on the computer which is designed to control the device.
This device object represents the printer and its physical structure modes that allow your computer’s operating system to control its functions.
When we choose an operation (like Control + P to print a document) on the printer then this command goes to the device driver through the kernel of the operating system.
Resultantly a calling program invokes a routine in the device driver and the driver issues corresponding commands to the microcontrollers within the printer. Further these microcontrollers control the components of the printer like motors etc. to start printing the document.

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basic input/output system
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 the most basic computer driver in existence first program that boots when a PC turns on.
The BIOS is stored on memory built into the motherboard and is designed to boot the hardware connected to the PC, including the hard drives, video display output keyboard and mouse.

2. Motherboard Drivers
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Small programs that are read by either Windows or Linux and allow for basic computer functions while inside the operating system.
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These drivers normally include programs that allow broadband ports, USB ports and I/O ports for the mouse and keyboard.
Depending on the make of the motherboard, the drivers may also have basic drivers for video and audio support.
3. Hardware Drivers
 programs that are designed to allow pieces of computer hardware, such as expansion slots, to function on a computer. Video cards, sound cards, network cards and other expansion cards come with driver discs to ease the installation process of the hardware. Other devices, like certain kinds of digital cameras and MP3 players, have
PC drivers programmed into their software for easy use on most makes of personal computers.

3.Virtual Device Drivers
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Virtual device drivers are different than most drivers.
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 virtual device drivers emulate a piece of hardware and essentially trick the computer into thinking that it is reading from a piece of actual hardware.
A particularly popular use for virtual device drivers is with reading
.iso files without having an actual disc, using one of these drivers to emulate a CD or DVD drive.