PURPOSE: To eliminate a need of a complete aligner, in a system and method for data transfer between two data busses different in width.

CONSTITUTION: A byte tracking system 60 has a system bus 34 having 32-bit width. A system I/F 48 connects the system bus 34 to a FIFO buffer 42 and gives a 4-byte data word 62. The buffer 42 can be accessed for word read/write. A 4:1 multiplexer 64 is connected to the output side of the buffer 42 by a bus 66 having 32-bit width. Correct bytes 63 of the data word 62 are multiplexed and transmitted to an 8-bit output bus 68. A byte tracker circuit 70 controls the multiplexer 64 to determine which byte 63 should be sent to the output bus 68. The byte 63 given to the output bus 68 is serially converted by a P/S converter and is give to an encoder/decoder 36.