Is the web browser performance rule “only 2 requests in parallel per hostname” still correct?

Question

In his book \"High Performance Websites\" Steve Souders wrote (2007) that browsers limit parallel requests to a domain/hostname to two at a time. Is this still valid today?<

Answer 1

Almost incorrect today.

Most browsers have upgraded to 6 parallel connections. See Steve Souder's Browserscope > Network tab > Connections per Hostname. Older browsers still restrict to 2 connections - that may or may not be relevant to you depending on the browsers your application supports.