The invention introduces a method for executing host input-output (IO) commands, performed by a processing unit of a device side when loading and executing program code of a first layer, at least including: receiving a slot bit table (SBT) including an entry from a second layer, where each entry is associated with an IO operation; receiving a plurality of addresses of callback functions from the second layer; and repeatedly executing a loop until IO operations of the SBT have been processed completely, and, in each iteration of the loop, calling the callback functions implemented in the second layer for a write operation or a read operation of the SBT to drive the frontend interface through the second layer.