A Linker Core (リンカーコア Rinkā Koa) is a specialized organ in a mage or a knight's body that manifests and shapes mana into useful forms. The power potential of a mage thus depends on the capacity of their Linker Core, and, currently, any analysis of their abilities is done by examining their Linker Core.
In computer science, a linker is a special type of computer program that transforms compiled computer code into an executable program. Similarly, a Linker Core is an organ that transforms the energy calculations created by a mage, into a functional spell that can be implemented and stored. An alternate use for the term "core" refers to a central processing unit or CPU for short.
A mage's Linker Core can be forcibly removed from their bodies but it apparently regenerates with time. Nanoha Takamachi had her Linker Core stolen by Shamal in A's but still managed to fire a Starlight Breaker immediately afterwards, most likely because the Starlight Breaker had already been prepared and merely needed to be fired. Nanoha was unable to cast any magic at all for the next few days. In fact, the Book of Darkness relied on the Wolkenritter stealing others' Linker Cores, as they apparently also contain magical knowledge of the respective mage, i.e. spells that the Book needs to fill its 666 pages.
Species that are known to possess Linker Cores are:
- Humans (only mages)
- Wolkenritter (and probably other living programs like Materials, too)
- Unison Devices
- Artificial Mages
- Combat Cyborgs
Familiars are said to "share one heart" with their masters, which may mean that they effectively use their master's Linker Core for their magic. This is indirectly supported by the fact that familiars and their masters share all their knowledge of magical spells.