Indeed. Running the DMA at 4.77Mhz made a lot of sense in the context of the original PC and XT, especially since the 8237 was only rated for 5Mhz anyways...

Indeed. Running the DMA at 4.77Mhz made a lot of sense in the context of the original PC and XT, especially since the 8237 was only rated for 5Mhz anyways... [Not to mention that the 8088 took 4 cycles to read a byte from memory and 5 cycles to read a byte from I/O.] The true power of the 8237 was that it never touched the data byte itself: it just manipulated the bus lines, transferring a byte directly from I/O device to memory in just 4 cycles, much faster than the 8088 could ever manage.