Question: In the original film, the Discovery's onboard computer states: "I am a HAL 9000 Computer, Production Number 3. I became operational at the HAL plant in Urbana, Illinois, on the 12th of January, 1992." So, "HAL" was a manufacturer identification prefix (standing for Heuristically-programmed ALgorithmic Computers), "9000" was its model number, and "No.3" was its production lineage. In this sequel, however, Dr. Chandra is chatting with one of HAL's earth-based twin computers which has a feminine voice and is called "SAL"; but how can they arbitrarily change its manufacturer identification prefix? Being produced by the HAL plant in Urbana, Illinois, and being identical to the computer aboard the Discovery, the twin's name should have a different production number, but it should still be called "HAL," should it not?
Question: One thing that always confused me is why was it necessary to jettison Discovery after it was used as a booster rocket? Why couldn't they just keep it attached to the Leonov as they made their escape?
Answer: If they didn't, any further manoeuvring would require much more fuel. They would be moving the mass of two ships.
Answer: They needed to lighten their load, to make it go faster. In Back to the Future Part III, after hijacking the train, the Doc and Marty unhooked the passenger cars to lighten the load.
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.
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