A memory expansion board capable of holding up to 16 Mbytes of memory devices, using primarily 1 Mbit chips, in 2 Mbyte module increments, on a single IBM PC/AT compatible size board. The circuit board is so designed that when the memory expansion board is populated by modules and placed in a computer system it does not interfere with any of the other expansion slots within the computer system, all of the expansion slots being normally spaced apart. The memory expansion board also includes a means of protecting the memory expansion board and modules from damage due to misalignment when inserting the board and/or modules. When certain of the modules are inserted rotated 180 degrees the circuit board cannot be properly installed in the system board because of physical interference. Lastly, the memory expansion board includes a means for providing reduced length addressing memory lines to memory devices appearing on opposite sides of a circuit board.