With version 41, Google Chrome has used multi-threading to improve the page load time.
As shared in another post while talking about defer attribute here, whenever a browser finds a script tag in page then it puts HTML parser on hold and begins downloading the script.
Once the download is over, browser parses the script and then executes it.
For all this time, the HTML parser is on hold which increases the page load time and delays rendering.
Now, with version 41, Google Chrome has implemented multi-threading for async & defer scripts. This way, as soon as a browser finds an async or defer script tag, though it will start downloading it immediately, but for parsing such scripts it will not wait for the download to finish. Rather, for all such cases, browser will start a new thread for parsing them and this way, both download and parsing can take place parallely almost.
Thus, as soon as download of the script is over, parsing too will be over in short span of time after it, instead of beginning it from zero.
Such a change would surely improve the load time, though, the difference would be significant for scripts which are large in size.