Prior to the invention of the microprocessor PCB, a computer consisted of multiple printed circuit boards in a card-cage case with components connected by a backplane, a set of interconnected sockets. In very old designs the wires were discrete connections between card connector pins, but printed circuit boards soon became the standard practice PCB. The Central Processing Unit, memory and peripherals were housed on individual printed circuit boards which were plugged into the backplate.
During the late 1980s and 1990s, it became economical to move an increasing number of peripheral functions onto the motherboard. In the late 1980s, personal computer motherboards began to include single ICs (also called Super I/O chips) PCB capable of supporting a set of low-speed peripherals: keyboard, mouse, floppy disk drive PCB, serial ports, and parallel ports. By the late-1990s, many personal PCB computer motherboards supported a full range of audio, video, storage, and networking functions without the need for any expansion cards at all; higher-end systems for 3D gaming and computer graphics typically retained only the graphics card as a separate component PCB.
The most PCB popular computers such as the Apple II and IBM PC had published schematic diagrams and other documentation which permitted rapid PCB reverse-engineering and third-party replacement motherboards. Usually intended for building new computers compatible with the exemplars PCB, many motherboards offered additional performance or other features and were used to upgrade the manufacturer's original equipment.
