Mechanical units are composed of mechanical components and possibly a biological component. Most mechanical units are vehicles with a terran driver.
Due to their biological components, mechanical units are vulnerable to some special abilities, such as a queen's Spawn Broodling attacks. However, they are immune to some special abilities which can affect organic units, such as the science vessel's Irradiate ability.
A "subtype" of mechanical units exist in StarCraft – robotic. This category includes reavers, shuttles, observers, spider mines and interceptors. Robotic units are immune to certain spells mechanical units aren't – for example, they can not be the victim of spawn broodling – but otherwise, they are very similar.
Wings of LibertyEdit
Science vessels can repair nearby mechanical units.
Heart of the SwarmEdit
In multiplayer SCVs can repair mechanical terran and protoss units.