The Demon Summoning Computer
The first COMP was designed by Stephen Hawking lookalike Steven in the first Shin Megami Tensei. He gives it to the protagonist to try and fend off the invasion of demons inside of Tokyo. He later appears in Shin Megami Tensei II to give a COMP to Aleph. The COMP allows its user total control over his or her cadre of demons, at the expense of MAG.
The COMP appears slightly modified in the Devil Summoner series as a GUMP, or Gun Computer. A totally new type of COMP that looks suspiciously like a Nintendo DS was featured with mostly the same functionality as the old in Devil Survivor, or 3DS in the case of the Overclocked enhanced port.
The functionality of the COMP as a summoning and confinement device for demons seems to be based on the concepts taken from Renaissance era magic grimoires, such as the magic ring and Vessel of Brass of the Hebrew King Solomon. In legends attributed to Solomon, he was able to summon demons with the aid of his magic ring, said to be imprinted with the Seal of Solomon, now the same used as the Star of David in modern Judaism, and confined them within the Vessel of Brass, which was inlaid with Hebrew text and bound with magical seals and pentagrams. With both items, he was able to command the demons at his will to perform various tasks, the most notable of which was the construction of the First Temple in Jerusalem.
The COMP does not feature in Shin Megami Tensei: Nocturne, as the Demi-Fiend's demonic disposition allows him to summon demons at will. In Shin Megami Tensei: Strange Journey, a Demon Summoning Program is mysteriously downloaded onto the crew's Demonica Suits, allowing analogous functionality to that of a COMP.