Most of the overhead in file I/O involves accessing the media (the physical device). If you are reading or writing many small blocks of information, the media device can spend a lot of time seeking to find the physical location on the media for each read or write operation. In this case, better performance is achieved by using buffered file I/O. With buffered I/O, the file I/O manager maintains an intermediate buffer larger than the blocks of information you are reading or writing. It only accesses the media when the buffer must be filled from or written to the disk.
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