I was skeptical that it was a joke since it's quite a big coincidence, but according to Arthur C. Clarke: > ...about once a week some character spots the fact

I was skeptical that it was a joke since it's quite a big coincidence, but according to Arthur C. Clarke: > ...about once a week some character spots the fact that HAL is one letter ahead of IBM, and promptly assumes that Stanley and I were taking a crack at the estimable institution ... As it happened, IBM had given us a good deal of help, so we were quite embarrassed by this, and would have changed the name had we spotted the coincidence.