PIO

PIO, or Programmed Input/Output, is a method of transferring data from a device to another device, utilizing the computer processor and not the memory or DMA. Because PIO modes utilize the computer processor, using PIO is slower than DMA.

Note: There are no plans, and likely will never be plans, for a PIO Mode 5 (or anything beyond Mode 4), although some computer and hardware manufacturers have advertised computer or hardware with acceptance to PIO Mode 5. 

Also see: ATA, Bus mastering, DMA, Hard disk drive definitions, IDE