The present invention is directed to an interface. In an aspect of the present invention, an interface system suitable for coupling a bus interface controller with a back-end device includes a bus interface controller and a back-end device in which the back-end device is coupled to the bus interface controller via an interface. The interface includes a command queuing interface suitable for enqueueing a transaction, a command completion interface suitable for reporting transaction completion and a data transfer interface suitable for transferring data. The data transfer interface includes an inbound data transfer interface suitable for transferring data and an outbound data transfer interface suitable for transferring data. The inbound data transfer interface and the outbound data transfer interface are suitable for processing commands simultaneously.