Complex sentence: The 68000 has a 16-bit external data bus so must transfer 32 bits of data in two consecutive steps, a technique called multiplexing: all this is transparent to the software, which was 32-bit from the beginning.
Split into simpler sentences: The 68000 has a 16-bit external data bus so 32-bits of data is transferred in two consecutive steps, a technique called multiplexing. This is transparent to the software, which was 32-bit from the beginning.