Part II. Web Performance Optimization
Web performance optimization streamlines your content and tunes your server to deliver web pages faster. In the following chapters, you’ll learn how to optimize your web pages and multimedia, shrink your Cascading Style Sheet (CSS) and HTML file sizes, and reduce server requests with sprites and suturing. You’ll learn how to squeeze your Ajax code and make it more robust. You’ll explore advanced techniques such as improving parallel downloads, caching, HTTP compression, and URL rewriting.
Finally, in Chapter 10 you’ll read about best-practice metrics and tools to measure and optimize your search engine marketing (SEM) campaigns and improve website performance. First, let’s explore the user psychology of delay, and trends in web page growth.
The Psychology of Website Performance
Previous research has shown that user frustration increases when page load times exceed 8 to 10 seconds without feedback. ,  Newer evidence shows that broadband users are less tolerant of web page delays than narrowband users. A JupiterResearch survey found that 33% of broadband shoppers are unwilling to wait more than four seconds for a web page to load, whereas 43% of narrowband users will not wait more than six seconds. 
The Effects of Slow Download Times
Even small changes in response times can have significant effects. Google found that moving from a 10-result page loading in 0.4 seconds to a 30-result page loading ...