Professional Website Performance: Optimizing the Front-End and Back-End

Chapter 1

A Refresher on Web Browsers

WHAT’S IN THIS CHAPTER?

• Reviewing web browsers and the HTTP protocol
• Understanding the steps involved in loading a web page
• Getting to know Keep Alive and parallel downloading

To access a website, you need a web browser — the piece of client-side software that requests resources from a web server and then displays them. Web browsers are one of the most important pieces of software in the modern Internet, and competition between vendors is fierce — so much so that many vendors have chosen to give their browsers away for free, knowing that an increased share of the browser market can indirectly reap profits in other areas.

Although such competition is good news for consumers, it can be a different story for web developers, who must strive to make their sites display correctly in the myriad of browsers, each of which has its own idiosyncrasies and nonstandard behavior. To understand how this situation has evolved, let’s begin by returning to the early days of the World Wide Web.

A BRIEF HISTORY OF WEB BROWSERS

Although Mosaic is often thought of as the first web browser to hit the market, this isn’t actually true — that honor falls on WorldWideWeb, a browser developed by Tim Berners-Lee in 1990 at the same time as he developed the HTTP 0.9 protocol. Other browsers soon followed, including Erwise, ViolaWWW, MidasWWW, and Cello — with Cello being, at this point, the only browser for Microsoft Windows. The year 1992 also saw the release of Lynx, ...