Six months to 1 billion

So the iTunes Store just sold its three billionth song. Wow. That’s a lot of anything, regardless of what you’re counting. (OK, if you're counting grains of sand on the coastline of the United states, perhaps it's not a lot.) But more interesting to me is the pace at which Apple reached its latest billion-song threshold. It took the company a little less than three years to sell the first billion iTunes downloads. Then it took less than a year to sell the second billion. Now, just over six months later, the store has passed the three-billion song mark.

Looking at it as precisely as possible, if we assume that the two and three billion song targets were hit the same day as the press releases went out (January 9, 2007, and July 31, 2007, respectively), that means it took 203 days to sell one billion songs. That means the Store had to average about 4,926,108 song purchases per day, or 205,255 per hour. Breaking it down even further, that's 3,421 songs sold per minute, or an astounding 57 songs sold every second for those 203 days!

If each song is an average of 5MB, then the Store’s bandwidth usage—just for songs, not counting movies, TV shows, games, podcasts, or any other non-song-related Store item—is a staggering 1,002GB per hour . That’s nearly a terabyte of data transfer per hour, every hour, for those 203 days. Think about paying that bill from your ISP! “Yes, I’d like to know the cost of your 720TB per month data transfer plan, please.”

Clearly the rate of sales can’t continue to double every time the next billion song mark is reached, but Tuesday’ announcement makes it clear that the iTunes Store hasn’t yet reached a point where the growth rate is slowing. It will be interesting to see how long it takes for the next billion; the acceleration curve on the first three would point to something like three months from now, but that seems almost too fast to me. What do you think? Where is the iTunes Store on the unit sales curve? Will things continue to accelerate, or is six months as quickly as we’ll see a billion songs sold?

This story, "Six months to 1 billion" was originally published by PCWorld.

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