There is a new mysterious feature in the latest developer releases of Google’s Chrome browser. It is called “Prerendering” and is described to speculatively render entire websites in the background to make the pages available instantly when you click on a link. Subjectively, the promise of “wicked fast” page loading is not exaggerated, even if we have no clue how Google achieves this goal. Is this Chrome’s next big play?

      Web Page Prerendering recently surfaced as an option in Chromium’s flags, which can be enabled or disabled with a simple click. The description is mysteriously simple and short: “Speculatively prerenders complete webpages in the background for a faster browsing experience.” We have been playing with this feature for a few days now and have been trying to understand if Chrome prerenders pages, how it prerenders and when it prerenders. There is no real evidence that confirms that Chrome in fact prerenders pages – there is simply a subjective impression whether a page loads faster or not.

      Our opinion is that pages do load quite a bit faster, especially on smaller websites, which typically suffer from slow load times. ConceivablyTech no exception – while we work diligently to optimize our server as far as we can, there are limits and we are fully aware that our pages do not load as fast as pages on other, larger sites with possibly dozens or hundreds of servers. Google’s new prerendering appears to alleviate this issue as our article pages are significantly snappier. We noticed the same effect on other smaller sites as well as very complex pages such as CNN, which include external content and can have substantial delays when loading into a browser window.

      For example, the homepage of CNN took somewhere between 1295 ms and 3281 ms to load in Chrome 9.0 Dev. The data volume of the static website itself was about 1.26 MB, while external content added about 900 KB until the entire page was available in Chrome. We noticed that CNN’s article pages are at least 500 KB in size and were available without noticeable delay, almost instantly. You would expect Google to clog your available bandwidth to achieve this result. You would also expect a constant request of data from your PC and a constant flow of data to your PC. However, what we found is that data transfer volumes to the browser were not exceptionally high, in a range of less than 100 KB per minute. A spike in data transfer was noticed as soon as the mouse pointer was hovering above a link.

      You would also expect the cache of the browser to be built up beyond the elements of your current page. However, this was not the case. The browser cache simply stored the elements of the visited pages. It is entirely possible that Google stores the prerendering information somewhere else and it is more than likely that the entire data volume is stored in a format that can be read by Chrome much faster.

      Google declined to comment on this feature and did not provide details beyond what is publicly available, which is virtually zilch. What is rather unlikely, however, is that the prerendering feature is based on your browsing history. Those files are may largely be already available in your data cache and it may be a waste of time to re-render pages that are cached already.

      We found another new feature that substantially improves the time of web pages being available in the browser window. Google is now offering the “false start” feature through its flags options. Using “Snap Start”, Chrome uses an abbreviated handshake in a client-server connection that can dramatically speed up the loading of web pages. There is still some concern about this feature, as it requires server support and can, potentially, cause websites not to be available. However, we found this one to be especially effective during our testing. Compared to Chrome 5.0, which Google described as lightning fast, it appears that Chromium 9 is light years ahead just half a year later.

      If you are looking for plain benchmark numbers, there aren’t any effective ways to measure this advantage in a reliable and meaningful way – as these features depend on your Internet connection and browsing behavior. Chromium 9 is still about 15-20% ahead of Firefox 4 Beta 7 in JavaScript and is about twice as fast in Google’s V8 benchmark. However, the perceived speed advantage is massive. Mozilla and Microsoft should keep an eye on what Google is developing right now.

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