In 1987 four new 32-bit computer backplane buses joined FASTBUS (ANSI/IEEE Std. 960-1986) as IEEE standards. They are Futurebus (IEEE Std. 896.1), VME (IEEE Std. 1014), NuBus (IEEE Std. 1196), and Multibus-II (IEEE Std. 1296). The author compares and contrasts these buses, discusses their strengths and weaknesses, and considers possible directions for future improvement. He discusses fundamental limits and ways in which they can be overcome.