Without device drivers, there is no functioning system.
User activities are performed by means of a set of standardized calls that are independent of the specific driver; mapping those calls to device-specific operations that act on real hardware is then the role of the device driver.
The role of a device driver is providing mechanism, not policy.
"what capabilities are to be provided"(the mechanism)
"how those capabilities can be used"(the policy)
Since different environments usually need to use hardware in different ways, it's important to be as policy free as possible.
It is a software layer that lies between the applications and the actual device.
Different drivers can offer different capabilities, even for the same device.
One of the good features of Linux is the ability to extend at runtime the set of features offered by the kernel.
Each piece of code that can be added to the kernel at runtime is called a module.
The Unix way of looking at devices distinguishes between three device types. Each module usually implements one of these types, and thus is classifiable as a char module, a block module, or a network module.
Every software package used in a Linux system has its own release number, and there are often interdependencies across them: you need a particular version of one package to run a particular version of another package.
to be continued...