What is an I/O buffer? What is the advantage of buffering? Is buffering always effective? Justify your answer with help of an example.

One kind of I/O requirement arises from devices that have a very high character density such as tapes and disks. With these characteristics, it is not possible to regulate communication with devices on a character-by-character basis. The information transfer, therefore, is regulated in blocks of information. Additionally, sometimes this may require some kind of format control to structure the information to suit the device and/or data characteristics. 

For instance, a disk drive differs from a line printer or an image scanner. For each of these devices, the format and structure of information is different. It should be observed that the rate at which a device may provide data and the rates at which an end application may consume it might be considerably different. In spite of these differences, the OS should provide uniform and easy to use I/O mechanisms. Usually, this is done by providing a I/O buffer. The OS manages this buffer so as to be able to comply with the requirements of both the producer and consumer of data. Basically, the buffers absorb mismatch in the data transfer rates of processor or memory on one side and device on the other.