3 terabytes

From The Signal and the Noise by Nate Silver. Page 12.

The human brain is quite remarkable; it can store perhaps three terabytes of information. And yet that is only about one one-millionth of the information that IBM says is now produced in the world each day. So we have to be terribly selective about the information we choose to remember.

The source for the information is from IBM.

What is big data?
Every day, we create 2.5 quintillion bytes of data — so much that 90% of the data in the world today has been created in the last two years alone. This data comes from everywhere: sensors used to gather climate information, posts to social media sites, digital pictures and videos, purchase transaction records, and cell phone GPS signals to name a few. This data is big data.

And from Robert Birge in Human Brain.

The typical adult human brain weighs about 3 pounds (1.4 kilograms). It contains several billion neurons connected at a hundred trillion synapses. The male brain is bigger; typically 1,300–1,500 cubic centimeters while the female's is typically 1,200–1,350 cubic centimeters. Volume, however, is not necessarily a figure of merit. Neanderthals had very large brains. Whales and dolphins have bigger brains than humans.

Robert Birge (Syracuse University) who studies the storage of data in proteins, estimated in 1996 that the memory capacity of the brain was between one and ten terabytes, with a most likely value of 3 terabytes. Such estimates are generally based on counting neurons and assuming each neuron holds 1 bit. Bear in mind that the brain has better algorithms for compressing certain types of information than computers do.