Dr. Heywood Floyd: I do seem to remember a process where you people ask me questions and I give you answers, and then I ask you questions and you give me answers, and that's the way we find out things. I think I read that in a manual somewhere.
HAL 9000: I'm completely operational, and all my circuits are functioning perfectly.
HAL-9000: What is going to happen?
Dave: Something wonderful.
HAL-9000: I'm afraid.
Dave: Don't be. We'll be together.
HAL-9000: Where will we be?
Dave: Where I am now.
Answer: The most likely reason the name was changed was probably a literary one. It makes it easier for the audience to differentiate SAL from HAL, showing how they are two distinct computers playing different roles in the film. It may also just be a feminine nickname being that SAL has a female voice.
raywest ★
I thought perhaps "SAL" was a nickname, also, until I saw that the computer's maker nameplate reads "SAL 9000" (visible in close-ups of SAL's glowing eye).
Charles Austin Miller