A high-density server includes a plurality of server enclosures, each of which includes an enclosure frame with a pair of front decks and a rear opening, an enclosure element having a power supply unit, and a pair of server modules having module connectors. The enclosure element is positioned in the rear side of the enclosure frame. The module connector of the server module is detachably connected to the front connector of the power supply unit when the server module moves along the front deck in an insertable/removable manner inside the enclosure frame. A cooling fan is positioned in the front side of the server module relative to the rear opening of the enclosure frame. An external interface is attached to the rear end of the server module or installed in the enclosure element, thus preventing a mess in the front face of the server enclosure due to external wires.