Tim Berners-Lee borrowed the URL’s double slash from an Apollo workstation
An original BCS interview supplies his alternative address spelling, while a 1997 technical email explains the job those punctuation marks were meant to do.
The web’s inventor had second thoughts about the punctuation everybody learned to say out loud. Tim Berners-Lee told BCS he would have left out the double slash. Before giving those two characters a retirement party, though, there is an earlier email worth opening.
In January 1997, Berners-Lee explained the design on the W3C’s public URI mailing list. The distinction came from Apollo’s Domain file system: a path could start from the local machine or from the surrounding network. The paired slashes marked a different starting scope. They had a job before they became something a radio presenter had to pronounce.
Think about giving directions from your kitchen versus giving directions from the town center. The instructions after the starting point can be identical while sending somebody to a completely different place. The punctuation tells the reader which starting point applies, with considerably less room for “you know, over there.”
Berners-Lee used telephone numbers to illustrate the same idea, then generalized the hierarchy far enough to include Earth and Mars. A web address debate with room for another planet is thoroughly committed to future compatibility. Most of us would settle for the printer staying connected (small ambitions).
The original BCS interview, “Isn’t it semantic?”, gives the other half. Interviewer Brian Runciman asked what he would do differently after roughly fifteen years of the web. Berners-Lee’s reply included “I would have skipped on the double slash” and proposed reversing the order of the domain. The interview introduces the approaching www2006 conference, which places this exchange before the often-cited 2009 coverage.
His example was http:uk/org/bcs/members. Reading the larger grouping first would let a hierarchy continue in one direction through the organization and down to members. That makes the suggestion more interesting than the usual story about two useless keystrokes. He was reconsidering where an address should put its boundaries.
An established address system carries everyone else’s saved references along with it. Changing an attractive detail can require changing the tools and assumptions surrounding the detail, too. A URL parser exists because those boundaries need one consistent interpretation; counting slashes by eye would be a strange place to economize.
Future address systems may hide even more of their syntax from the people using them. The problem of choosing the right scope will remain underneath, wherever the interface puts it. Berners-Lee’s own example left a wonderfully specific unresolved destination in that hierarchy: Mars had a canal and a crater waiting for an address.
Mars got a path, too.