 The 86b was larger (about 3x higher than the 86a or 1.5x higher than an IBM PC) due to the need of an expansion box with room for extension cards, two full height FDD's and extra power supply.The 86a could be field upgraded to 86b by adding the expansion box on top of the 86a unit and replacing the ROM Basic with a BIOS ROM.The case was black plastic with room for storing the full size IBM compatible keyboard.