Abstract: To effect a block data transfer between a plurality of physical I/O devices coupled through interfaces to an I/O channel ("IOC") bus, a source logical device is established by programmably assigning to each of the physical device interfaces a logical device identifier, a leaf identifier determining when the physical device participates relative to the first data transfer in the block data transfer, a burst count specifying the number of consecutive transfers for which the physical device is responsible when its interleave period arrives, and an interleave factor identifying how often the physical device participates in the block data transfer. A destination logical device is similarly established. The source and logical devices are then activated to accomplish a block transfer of data between them.