Over the years I have met many people in many professions: actors, writers, biologists, computer pioneers, artists, astronomers, composers, even a trio of Nobel Prize winners in physics. They had numerous and diverse skills. What none of them had was a good memory. Or rather, what none of them would admit to was a good memory. Their emphasis was the other way round: how hard it was to recall people's faces, or names, or birthdays, or travel directions.

History records examples of people with prodigious memories. Mozart, at thirteen, went to the Sistine chapel in Rome to hear a famous "Miserere" by Allegri, then wrote out the whole work. The mathematician, Gauss, did not need to look up values in logarithm tables, because he knew those tables by heart. And Thomas Babington, Lord Macaulay, seemed to have read so much and remembered it so exactly that one of his exasperated colleagues, Lord Melbourne, said, "I wish I was as cocksure of anything as Tom Macaulay is of everything."

To the rest of us, hard-pressed to remember our own sister's phone number, such monster memories seem almost inhuman. My bet, however, is that even these people would, if asked, complain of their poor memories and emphasize what they forgot. And each of us, without ever thinking about it, has enormous amounts of learned information stored away in our brain.

I say "learned information," because some of what we know is "hard-wired," and we call that instinct. We don't learn to suck, to crawl, or to walk by committing actions to memory, and we normally reserve the word "memorize" for things that we learn about the world through observation and experience. I am going to stick with this distinction between instinct and memory, though sometimes the borderline becomes blurred

We don't remember learning to talk, but we accept that it relies on memory because others tell us we did (though there is good evidence that the ability to acquire language is hard-wired). And most of us would not say that riding a bicycle depends on memory, although clearly this is a learned and not an inborn activity.

I want to concentrate on factual information that is definitely learned, stored, and recalled, and ask two simple questions: Where is it stored, and how is it stored?

The easy part first: information is stored in the brain. But when we ask where in the brain, and ask for the form of storage, we run at once into problems. The tempting answer, that a piece of data is stored in a single definite location, as it would be in a computer, proves to be wrong. Although many people believe that the brain ultimately operates like a computer - a "computer made of meat" - in this case the analogy is more misleading than helpful.

Much of what we know about memory comes from the study of unfortunate individuals with brains damaged by accident or disease. This is hardly surprising, since volunteers for brain experiments are hard to come by. (As Woody Allen remarked, "Not my brain. It's my second favorite organ.")

Studies of abnormal brains can be misleading, but they show unambiguously that a human memory does not sit in a single defined place. Rather, each memory seems to be stored in a distributed form, scattered somehow in bits and pieces at many different physical locations. Although ultimately the information must be stored in the brain's neurons (we know of nowhere else that it could be stored), we do not yet understand the mechanism. Some unknown process hears the question, "Who delivered the Gettysburg address?" goes off into the interior of the brain, finds and assembles information, and returns the answer (or occasionally, and frustratingly, fails to return the answer): "Abraham Lincoln."

And it does the job fast. The brain contains a hundred billion neurons, but the whole process, from hearing the question to retrieving and speaking the answer, takes only a fraction of a second.

We may not be Mozart, but each of us possesses an incredible ability to store and recall information. Does this impress us? Not at all. Instead of being pleased by such a colossal capability, we are like the celebrated Mr. X, always complaining about his sieve-like memory.

I would give Mr. X's name, but at the moment I cannot quite recall it.

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