The Supercomputer (スーパーコンピューター) was a miniature supercomputer that Sailor Mercury owned which could be used to scan surroundings and analyze data, proving very useful in battle. It was given to her by Luna. For some reason it was not seen or used often after the first season.
Sailor Mercury's Supercomputer appears first in Act 03, Volume 01. It gives Sailor Mercury the ability to analyze and solve very complex and scientific problems with ease, and can find weak points in enemies.
As the smartest and most intelligent of the Sailor team, the Supercomputer was given to Sailor Mercury by Luna in episode 9. It can be used to analyze enemies and other objects upon which data is needed, enabling her to find weak points in her enemies. Ami can also use the computer to communicate with the other senshi through their communication devices, as seen in episode 057.
In the anime, the computer once had a message on it that referenced the movie "RoboCop".