A modular system architecture that uses 3.5" square boards that snap together. PC/104 products are widely used because this "stack through" bus architecture provides a compact and rugged design for building process control and embedded systems. PC/104 boards use the earlier ISA bus, while PC/104+ refers to PCI-based boards.
PC/104 Boards
The top board is a complete PC from Intelec Technologies. The bottom one could be a data acquisition board or any other peripheral not part of the primary PC. The stacking pins and sockets (arrows) connect the boards together and are common on all PC/104 boards. The other pins on the perimeter depend on their function, which in this example indicate a large number of I/O connections.