Gramps Unit is the name given to an ambiguous and antique computer.
Originally, he was shown to take up an entire basement as Whirlwind and Univac era mechanical computers do. He requires extensive electricity which explains one reason why Mom Unit is concerned about fuel. Starting up Gramps Unit is very complex and requires many buttons and levers. This was a rhythmic theme spoken by children in the background. By season 2 episodes, there were no more children speaking in the background during the title cards, and that means this theme was forgotten about as well. When Gramps Unit was started up, he required data to analyze and was unable to communicate unless data was manually fed to him. The calculations were later printed out and also spoken by him. He does not seem to be completely conscious, but he does have a belief that Robots are superior and coexisting with humans is impossible. Gramps Unit often burned out some of his relays and some of his parts were knocked loose, leading to Robot Jones to consider that "Gramps Unit is just an old bucket of bolts.".
The next design showed him to be much more active and holding the capabilities of a Cray or D.E.C. supercomputer. He is also shown to run the house and act as a security system. He displays the same eccentric behavior as Dad Unit around humans and will try to zap them. This design was so sophisticated that he needed as many buttons and levers to push to be taken offline as the earlier version needed to be put online. When he was restarted, he noticed humans inside the house but that they were invited by Robot Jones. Together, Robot Jones and Gramps Unit told Dad Unit and Mom Unit that Robot wanted to study humans and that Gramps Unit invited some over.
This third design resembles a rack server with his signature magnetic tape reels and is now able to fit inside the family motorhome. He is able to run with a single electrical wire instead of the first design, which requires numerous electrical wires. The newest design of Gramps Unit enables him to run off of batteries when this single electrical wire is not plugged in.
It is unsure who Gramps Unit is supposed to be the parent for. But since there are inconsistent designs with Gramps Unit, it is possible that there is a Gramps Unit being a parent of Dad Unit as well as a Gramps Unit being a parent for Mom Unit. It could be that the first two designs are the same Gramps Unit who recieved upgrades to be able to run continuously and automatically. It could also be that the second and third designs are supposed to be the same Gramps Unit, with the capability of barely fitting inside the family motorhome. It could also be that each design is completely separate, meaning that the first Gramps Unit is supposed to be the Great Grandfather for Robot Jones. Based off of the similarities with the very first Gramps Unit requiring numerous electrical wires and the need of fuel conscious Mom Unit to supply fuel, it is possible that this Gramps Unit is the father for Mom Unit; and also since the second design's personality is very similar to Dad Unit, the second design is supposed to be the father for Dad Unit.