An expansion module for a computing unit of a High-Performance Computer cabinet, the expansion module comprising a casing configured to be removably guided horizontally in a main housing of a computing unit of a High-Performance Computer cabinet, a support card, mounted within the casing, comprising at least one module connector, said module connector being configured to be removably connected to the computing unit, a plurality of card slots connectors, each card slot connector being configured to be removably connected to an expansion card, at least a lever for locking/unlocking the casing to the main housing of the computing unit, said lever being operable manually without using any tools and a handle, pivotable according to a vertical axis, configured for locking/unlocking simultaneously the expansion cards when mounted in the card slot connectors.