Deep Thought was Deep Blue's ancestor; a chess-playing supercomputer named after the computer in The Hitchhiker's Guide to the Galaxy. Constructed in 1988 by a team of grad students at Carnegie Mellon University, it originally had 2 processors and could calculate 750,000 positions per second. It received a performance rating of ELO 2450.

In 1989, Deep Thought was upgraded to contain 6 processors and analyze 2,000,000 positions per second. It was beaten by Gary Kasparov in 41 moves that year, but in 1993 it defeated the youngest grandmaster in history, Judit Polgar. IBM soon began sponsoring the project and Deep Blue was born.