The CPU can start processing a block once its transfer to main memory is completd; at the same time the disk I/O processor can be reading and transfering the next block into a different buffer. This technique is called double buffering and can also be used to write a continuous stream of blocks from memory to the disk. Double buffering permits continuous reading or writing of data on consecutive disk blocks, which eliminates the seek time and rotational delay for all but the first block transfer. Moreover, data is kept ready for processing, thus reducing the waiting time in the program.

Elmasri and Navathe, Fundamentals of Database Systems 3rd., Addison-Wesley, pp. 127-128, 2000

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Double buffer is a designation of disk reading/writing algorithm different from the archaic video memory access method.