HAL, possibly the film's principal character, whether programmed or genuine, with emotions greater than those of the astronauts, is initially the only one who shows fully-realised human characteristics. Only HAL knows the real mission of the journey - both astronauts are unaware of the purpose of their Jupiter mission. The programmed computer has been designed to withhold vital information from the astronauts until the spacecraft is almost at the destination. It is only when the astronauts begin to question HAL's decision making, in terms of putting their lives at risk, that their own human instincts and emotions come to the fore. It is with the realisation that HAL is out of control that Dave ultimately decides he must switch him off.
IBM contributed advice about computers of the future, but insisted that their logos be removed from the on-board computer once they realised that it was to become an errant device. IBM was even less pleased when it was realised that HAL, the name of the computer, was IBM's name with all the letters displaced by one character. The producers maintain that this was coincidence, but the conspiracy theorists maintain that it was Kubrick and Clarke having a swipe at the computer company. The included letter is a very rare and significant handwritten document directly from the film's principal writer, that reiterates and ultimately confirms that the name choice was not made with any pre-meditated link to IBM, however subtle, (originally, the computer was to be named Athena and to possess a female voice).