Memory core

Memory cores are the devices which contain the memories of a Transformer.

Generation 1 cartoon
Once he began working on Optimus Prime, the Quintesson tasked with reviving the Autobot leader noted that his memory core was still intact, which would go a long toward restoring him.

Transformers Animated
Memory cores have some protection against a low-level Electromagnetic pulse, but higher level pulses can utterly wipe them, destroying the Transformer's memory.