The PC/104 standard defines an ultra-compact, modular, and stackable version of the PC (ISA) bus. The PC/104 form factor features full hardware and software compatibility with the PC bus.
PC/104 modules measure 3.6" x 3.8" and are stacked 0.6" apart. Stacking does not require a backplane or card cage. This design makes a three-module stack measuring only 3.6" x 3.8" x 2" possible. Now you can put a PC system anywhere, even in locations where space is at a premium.