Archecores form the driving force behind Arche-Ymirus mechs. They are capable of providing an endless stream of activated blue crystal energy to fuel high performance over an extended period of time.
Blue crystal engines come in different grades. In addition to the Archecores discovered in the Arche ruins, humans have also developed the blue crystal steam engine and various other power systems consisting of small-scale motors connected to crystallis hydraulics. These systems make imperfect use of blue crystal energy, with efficiency vastly inferior to Archecores. Steam engines are mostly installed in pseudo-Ymirus mechs and other war machines, while Arche Knights are usually equipped with crystallis hydraulics. 
But because most people have at best a limited understanding of technology, these systems are often referred to as Arche engines, Arche motors, or simply—and incorrectly—as Archecores.

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For the sake of distinguishing them from the various human-invented systems, the superior power cores excavated from ancient ruins are referred to as true Archecores.