Character Drivers and Block Drivers

I am stuck here for over a week. Actually I cannot decide what to do. The materials I have found so far, everybody seems to be concerned to dive into programming stuff rather than describing what is it. Well, I am trying to define some definition stuff without getting into much programming.


Character Devices and character drivers:

Character devices can be accessed as a stream of bytes, and this job is done by character drivers. Which means, the driver can access the device and transfer data as characters. The benefit of this method is, if the device is a sequential access device - character by character data transfer method is the most effective one. And we can use this method almost everything. Even if the device is a random-access device, we can emulate/pretend that the device is a sequential access device.

The serial port is the most familiar and widely used character device (/dev/ttys0). Character devices are represented by file nodes, and all the nodes are mounted on /dev directory. Though this device is treated as a file system, we cannot manipulate this file as conventional file (naturally).


Block devices and block drivers

Block devices are accessed by filesystem nodes just like a char device does (in /dev directory). It is treated like char devices almost in all ways, except one. That is, it trasnfers data by blocks (1KB per block, usually). And that gave the block devices the power of hosting the filesystems itself (disks, storage). Block devices are usually the disks and other storage devices, and virtual filesystems. Block devices are managed by kernel itself.


Here is a little note on linux file systems. click here

A little comparison

So in Linux, devices are treated as files. The benefit is, a common structure can be used for talking to all the devices. The idea nice. Then why do we have block drivers and character drivers. We could have done everything by character drivers. But the problem occurs when the random-access devices comes in. For example, if we use large storage devices, using character drivers won't be efficient, we need block drivers in this case. Again, for a keyboard, using a block driver is useless. So, we need these two distinct drivers.