What is an I/O buffer?

I/O buffer:

One type of input-output requirement arises from devices which have a very high character density as disks and tapes. With these characteristics, this is impossible to regulate communication along with devices upon a character-by-character basis. The information transfer, thus, is regulated into blocks of information. Furthermore, sometimes it may need several kind of format control to structure the information to suits the device or and data characteristics.

For example, a disk drive is different from a line printer or an image scanner.