1. An information processing system comprising: a control central processing unit; a memory; a serial interface coupled to a host apparatus to receive a first firmware; and a stream interface configured to receive an input stream including data to be processed and a second firmware and transfer the input stream to the memory, the stream interface being different from the serial interface, wherein the first firmware is executed to set, to the stream interface, a stream port for receiving stream data including a second firmware, wherein a download process in which the stream interface set by the first firmware receives the stream data including the second firmware and stores the stream data in the memory is executed in response to an instruction from the control central processing unit, and the control central processing unit analyzes the stream data stored in the memory to extract the second firmware in the memory space and executes the second firmware extracted in the memory space to process the data to be processed, wherein the stream interface detects synchronization upon reception of the input stream including the data to be processed, and the control central processing unit sets the stream interface so as to disable the synchronization detecting function before instructing the execution of the download process.