I/O devices are typically classified as either character-mode or block-mode devices. Character-mode devices facilitate unstructured data transfer with the system, where each byte of data is dispatched and received independently. Block-mode devices, on the other hand, are designed to send large amounts of data in a single operation, usually in fixed-length blocks or frames. This allows for more efficient data transfer but is useful only if the data files are structured and organized beforehand. Furthermore, block mode transfers typically require a special protocol interface depending on different OS companies.