Then, with a thrill of recognition, Bowman could often glimpse familiar coastlines, shining in that spectral lunar light. And sometimes, when the Pacific was calm, he could even see the moonglow shimmering across its face; and he would remember nights beneath the palm trees of tropical lagoons.

Yet he had no regrets for these lost beauties. He had enjoyed them all, in his thirty-five years of life; and he was determined to enjoy them again, when he returned rich and famous. Meanwhile, distance made them all the more precious.

The sixth member of the crew cared for none of these things, for it was not human. It was the highly advanced HAL 9000 computer, the brain and nervous system of the ship.

Hal (for Heuristically programmed ALgorithmic computer, no less) was a masterwork of the third computer breakthrough. These seemed to occur at intervals of twenty years, and the thought that another one was now imminent already worried a great many people.

The first had been in the 1940s, when the long-obsolete vacuum tube had made possible such clumsy, high-speed morons as ENIAC and its successors. Then, in the 1960s, solid-state microelectronics had been perfected. With its advent, it was clear that artificial intelligences at least as powerful as Man's need be no larger than office desks – if one only knew how to construct them.

Probably no one would ever know this; it did not matter. In the 1980s, Minsky and Good had shown how neural networks could be generated automatically – self replicated – in accordance with any arbitrary learning program. Artificial brains could be grown by a process strikingly analogous to the development of a human brain. In any given case, the precise details would never be known, and even if they were, they would be millions of times too complex for human understanding. Whatever way it worked, the final result was a machine intelligence that could reproduce – some philosophers still preferred to use the word "mimic" – most of the activities of the human brain – and with far greater speed and reliability. It was extremely expensive, and only a few units of the HAL9000 series had yet been built; but the old jest that it would always be easier to make organic brains by unskilled labor was beginning to sound a little hollow.

Hal had been trained for this mission as thoroughly as his human colleagues – and at many times their rate of input, for in addition to his intrinsic speed, he never slept. His prime task was to monitor the life-support systems, continually checking oxygen pressure, temperature, hull leakage, radiation, and all the other interlocking factors upon which the lives of the fragile human cargo depended. He could carry out the intricate navigational corrections, and execute the necessary flight maneuvers when it was time to change course. And he could watch over the hibernators, making any necessary adjustments to their environment and doling out the minute quantities of intravenous fluids that kept them alive.

The first generations of computers had received their inputs through glorified typewriter keyboards, and had replied through high-speed printers and visual displays. Hal could do this when necessary, but most of his communication with his shipmates was by means of the spoken word. Poole and Bowman could talk to Hal as if he were a human being and he would reply in the perfect idiomatic English he had learned during the fleeting weeks of his electronic childhood.

Whether Hal could actually think was a question which had been settled by the British mathematician Alan Turing back in the 1940s. Turing had pointed out that, if one could carry out a prolonged conversation with a machine – whether by typewriter or microphone was immaterial – without being able to distinguish between its replies and those that a man might give, then the machine was thinking, by any sensible definition of the word. Hal could pass the Turing test with ease.

The time might even come when Hal would take command of the ship. In an emergency, if no one answered his signals, he would attempt to wake the sleeping members of the crew, by electrical and chemical stimulation. If they did not respond, he would radio Earth for further orders.

And then, if there was no reply from Earth, he would take what measures he deemed necessary to safeguard the ship and to continue the mission – whose real purpose he alone knew, and which his human colleagues could never have guessed.

Poole and Bowman had often humorously referred to themselves as caretakers or janitors aboard a ship that could really run itself. They would have been astonished, and more than a little indignant, to discover how much truth that jest contained.

The day-by-day running of the ship had been planned with great care, and – theoretically at least – Bowman and Poole knew what they would be doing at every moment of the twenty-four hours. They operated on a twelve-hours-on, twelve-hours-off basis, taking charge alternately, and never being both asleep at the same time. The officer on duty remained on the Control Deck, while his deputy saw to the general housekeeping, inspected the ship, coped with the odd jobs that constantly arose, or relaxed in his cubicle.

Although Bowman was nominal Captain on this phase of the mission, no outside observer could have deduced the fact. He and Poole switched roles, rank, and responsibilities completely every twelve hours. This kept them both at peak training, minimized the chances of friction, and helped toward the goal of 100 percent redundancy.

Bowman's day began at 0600, ship's time – the Universal Ephemeris Time of the astronomers. If he was late, Hal had a variety of beeps and chimes to remind him of his duty, but they had never been used. As a test, Poole had once switched off the alarm; Bowman had still risen automatically at the right time.

His first official act of the day would be to advance the Master Hibernation Timer twelve hours. If this operation was missed twice in a row, Hal would assume that both he and Poole had been incapacitated, and would take the necessary emergency action.

Bowman would attend to his toilet, and do his isometric exercises, before settling down to breakfast and the morning's radio-fax edition of the World Times. On Earth, he never read the paper as carefully as he did now; even the smallest items of society gossip, the most fleeting political rumors, seemed of absorbing interest as it flashed across the screen.

At 0700 he would officially relieve Poole on the Control Deck, bringing him a squeeze-tube of coffee from the kitchen. If – as was usually the case – there was nothing to report and no action to be taken, he would settle down to check all the instrument readings, and would run through a series of tests designed to spot possible malfunctions. By 1000 this would be finished, and he would start on a study period.

Bowman had been a student for more than half his life; he would continue to be one until he retired. Thanks to the twentieth-century revolution in training and information-handling techniques, he already possessed the equivalent of two or three college educations – and, what was more, he could remember 90 percent of what he had learned.

Fifty years ago, he would have been considered a specialist in applied astronomy, cybernetics, and space propulsion systems – yet he was prone to deny, with genuine indignation, that he was a specialist at all. Bowman had never found it possible to focus his interest exclusively on any subject; despite the dark warnings of his instructors, he had insisted on taking his Master's degree in General Astronautics – a course with a vague and woolly syllabus, designed for those whose IQs were in the low 130s and who would never reach the top ranks of their profession.

His decision had been right; that very refusal to specialize had made him uniquely qualified for his present task. In much the same way Frank Poole – who sometimes disparagingly called himself "General Practitioner in space biology" – had been an ideal choice as his deputy. The two of them, with, if necessary, help from Hal's vast stores of information, could cope with any problems likely to arise during the voyage – as long as they kept their minds alert and receptive, and continually reengraved old patterns of memory.