Fireship — Joan D. Vinge

Ethan Ring was on the run with a half-million dollar price on his head -- for Ethan was the amazing fusion of an ordinary man and the most incredible computer ever devised -- and the man had decided to run with his other half to Khorram Kabir's fantastic casino on Mars. But unscrupulous people knew he was there and he was blackmailed in order to penetrate Kabir's planet-wide computer networ, or die ...