But with the invention of the web in 1990 came an explosion in popular demand. It was soon clear that it was only a matter of time before the internet would exhaust its supply of addresses. Work on a replacement for IPv4 began in the early 1990s, with IPv6 finally being made available around 1998 (IPv5 was an experimental protocol for streaming audio and video that has since ceased to exist). By giving the new internet version an address space of 128 bits, the designers pretty well guaranteed that it would not run out of unique identifiers for decades, or even centuries, to come.
Two raised to the 128th power is an astronomical number. In decimal terms, it is roughly 340 billion billion billion billion—or, as Martin Levy of Hurricane Electric likes to say, “more than four quadrillion addresses for every star in the observable universe.”