A Blue Box, also known as a Plasma Positronic Harddrive Core, holds the soul/mind of a sentient robot. It is also called a Thought Matrix
As its name suggests, it resembles a blue box. It appears as a blue cube with energy swirling inside and flashes of electricity.
The mind held in a blue box is sentient and fully capable of emotion. While its exact manner of construction is not known, what is known is that it needs plasma to continue functioning. A blue box is a dynamic memory-processor matrix, it is able to generate new connections between memories and processing, allowing a robotic mind to mimic and organic mind in term of thought processing.