## Saturday 18 July 2009

### How long is a Petabyte life?

I have been thinking about Petabytes and tryng to get some perspective on how much data that really is.

In digital data terms a petabyte is a lot of data. 1 PB = 1,000,000,000,000,000 B = 1015 byte. Assuming a byte is 8 bits then a petabyte is 8 x 1015 bits.

According to this paper, Google processes more than 20 Petabytes of data per day using its MapReduce program.

According to Kevin Kelly of the New York Times, this reference, "the entire works of humankind, from the beginning of recorded history, in all languages" would amount to 50 petabytes of data.

These are all difficult to understand as they are abstract. So I tried to find a way of understanding what a Petabyte is in human terms. Scientific researchers estimate that the human retina communicates with the brain at a rate of 10 million bits per second (Reference HERE) or 106 bits per second. This sounds pretty impressive. How long does it take a human eye-brain system to move a petabyte of data (assuming that you could keep your eyes permanently open so that you are getting your full 10 million bits per second).

By my calculations a year is 3.15 x 107 seconds. This means a total amount of data per year from retina to brain of 3.15 x 1013 bits. Dividing 8 x 1015 by 3.15 x 1013 we get 254 years. This is a long time to keep your eyes open!

If we take a normal human life to be the biblical standard of Psalms 90: The days of our years are threescore years and ten, then a normal human creates about 0.27 petabytes in their life.

So I will define a new unit, the PetaBlife, with a symbol which is the number of standard human lifetimes required for a human retina to make a PetaByte of data.

If we take Google seriously, then each year they are processing the equivalent of 7.3 x 103 ℘.

Matt