A data transfer system having a transfer discrimination circuit for discriminating the type of data transfer between an input/output channel device and I/O devices for a computer includes a transfer discrimination circuit. This circuit includes a edge detection unit operating in response to a tag signal supplied to the edge detection unit for detecting the trailing edge of the tag signal after a leading edge of the tag signal has passed. The edge detection unit having a leading edge detector, a trailing edge detector, a storage element, and logic gate circuits. A timing unit is included operating in response to the output of the edge detection unit for counting a predetermined time, along with a discrimination storage unit operating in response to the output of the timing unit for delivering an output indicating an interlock data transfer or an output indicating a data streaming feature data transfer.