There are many types of motherboards ranging in size and shape. The first motherboard appeared in 1981 and was made by IBM PC. It measured 8” x 11.5” and had five expansion slots that were positioned 1” apart in the back, left of the board.
The XT(Extended Technology) computer came about in 1982 and measured about 8.5” x 12” inches. This board had a total of eight expansion slots positioned at 0.8” apart.
The first AT(Advanced Technology) board measured 12” x 13.5” and also had eight expansion slots spaced 0.8” apart. The popular form of the AT became the main model made by manufacturers.