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 type of I/O requirement arises from devices which have a very high character density like tapes and disks. With these attributes, it is not possible to regulate communication along with devices on a character-by-character basis. Hence, the information transfer is regulated in blocks of information. In addition, sometimes this may need some type of format control to structure the information to suit the device and/or data characteristics. For example, a disk drive is different from a line printer or an image scanner.

For each of these devices, the format and structure of information is dissimilar. It should be examined that the rate at which a device may offer data and the rates at which an end application may consume it might be significantly different. In place of these differences, the OS should offer uniform and easy to use I/O mechanisms. Generally, this is done by providing an I/O buffer. The OS manages this buffer thus as to be able to comply with the requirements of both the producer and consumer of data. Essentially, the buffers absorb mismatch in the data transfer rates of processor or memory on one side and device on the other.