The HP Internal Serial + PS/2 Port (part 56Q78AA) is an HP option kit that adds legacy connectivity to an HP business desktop. It consists of a full-height expansion-slot bracket carrying two PS/2 mini-DIN ports (keyboard and mouse) and one 9-pin D-sub RS-232 serial port, wired on a short internal cable to a header connector that plugs into the matching port on a compatible HP motherboard. It is used where older equipment still depends on these interfaces: point-of-sale terminals, barcode scanners and receipt printers with serial connections, industrial controllers, laboratory instruments, KVM switches, or PS/2 keyboards and mice in secure environments. Because it connects to an internal header rather than using a PCIe slot, it only works in HP desktops that provide the corresponding header - confirm compatibility against the QuickSpecs for your model before ordering. HP lists the kit at 315 x 58 x 20 mm and 52 g.