Website Performance: Tables Versus CSS

Most website designers have been using CSS for page layout for several years now, but I occasionally see some websites that continue to use HTML tables for layout. As I’ve been focusing on website performance lately, I’ve found some references that modern browsers render sites using tables for layout slower than they do sites that use CSS. I decided to investigate and confirmed that there are many possible situations where sites using large tables will appear to load much slower than those using CSS. I put together two pages to confirm:

This page uses <div> elements for layout
This pages uses a large table for layout

On both pages I’ve added a 5-second sleep near the end of the page to show what might happen if the server was slow, if there were network problems, or any other number of things may have happened.

Notice that the page created using a table changes a lot after the delay. I’ve tried it in Firefox 3 which extends the main (yellow) content section all of the way to the right until it receives the rest of the document, at which point it has to shrink that part to make room for the section on the right. Internet Explorer behaves even worse. It leaves a blank white page until after the delay, at which point it draws the whole table.

By contrast, the page created with CSS positioning shows all of the content above the delay and has it in the correct position. When the rest of the document is sent it just fills in the appropriate content, but doesn’t have to re-arrange anything on the page.

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