Many of you know that along with health I also have a passion for technology. The fact that a petabyte drive is real and will be here in seven years is absolutely amazing and will transform much of the way computers are used today.

So just how big is a petabyte drive and what could you put on it?

One certainty is that you will not fill the space with personal jottings or reading matter. In round numbers, a book is a megabyte. If you read one book a day for every day of your life for 80 years, your personal library will amount to less than 30 gigabytes. Remember a petabyte is 1 million gigabytes so you will still have 999,970 gigabytes left over.

To fill any appreciable fraction of the drive with text you'll need to acquire a major research library. The Library of Congress would be a good candidate; it is said to hold 24 million volumes, which would take up one-fiftieth of your disk. So you could fit 50 Library of Congresses on your petabyte drive.

Other kinds of information are bulkier than text. A picture, for example, is worth much more than a thousand words; for high-resolution images a round-number allocation might be 10 megabytes each.

And this is being generous. Most images from a digital camera are one to four megabytes, not 10. How many such pictures can a person look at in a lifetime? I can only guess, but 100 images a day certainly ought to be enough for a family album. After 80 years, that collection of snapshots would add up to 30 terabytes. So your petabyte disk will have 970,000 gigabytes left after a lifetime of high quality photos.

What about music? MP3 audio files run a megabyte a minute, more or less. At that rate, a lifetime of listening--24 hours a day, 7 days a week for 80 years--would consume 42 terabytes of disk space. So with all your music and pictures for a lifetime you will have 928,000 gigabytes free on your disk.

The one kind of content that might possibly overflow a petabyte disk is video. In the format used on DVDs, the data rate is about two gigabytes per hour. Thus the petabyte disk will hold some 500,000 hours worth of movies; if you want to watch them all day and all night without a break for popcorn, they will actually fill up your petabyte drive if you have a lifetime of video on it as it will give you 57 years of video.

But this would probably be more than enough for most people as who wants to see a picture of you sleeping for one-third of your life. However, a second petabyte derive could record every moment of life, in high-quality video, of the oldest person on earth.

Still another nagging question is how anyone will be able to organize and make sense of a personal archive amounting to 1 million gigabytes. Computer file systems and the human interface to them are already creaking under the strain of managing a few gigabytes; using the same tools to index the Library of Congress is unthinkable.

Perhaps this is the other side of the economic equation: information itself becomes free (or do I mean worthless?), but metadata--the means of organizing information--is priceless.

The notion that we may soon have a surplus of disk capacity is profoundly counterintuitive. A well-known corollary of Parkinson's Law says that data, like everything else, always expands to fill the volume allotted to it. Shortage of storage space has been a constant of human history; I have never met anyone who had a hard time filling up closets or bookshelves or file cabinets.

But closets and bookshelves and file cabinets don't double in size every year. Now it seems we face a curious Malthusian catastrophe of the information economy: the products of human creativity grow only arithmetically, whereas the capacity to store and distribute them increases geometrically. The human imagi