Microsoft says IE9 has parallel Javascript rendering and execution

Question

The new JavaScript engine takes advantage of multiple CPU cores through Windows to interpret, compile, and run code in parallel. - http://technet.microsoft.com/en-us/library/gg699435.aspx

and

The Chakra engine interprets, compiles, and executes code in parallel and takes advantage of multiple CPU cores, when available. - http://msdn.microsoft.com/en-us/ie/ff468705.aspx

Wait what?!? Does this mean that we have multi-threaded parallel execution of JavaScript code (outside of web workers) in IE9?

I think this is just a bad marketing trick, but I would like more information about this. Maybe they mean that different browser windows / tabs / processes can use multiple processors?

Answer 1

Conclusions based mainly on comments and therefore provided as an answer from the wiki community, so this question ends with the actual answer:

Microsoft probably means that individual tasks (i) interpret and / or work; and (ii) compilation occurs in parallel. They probably applied technologies such as the Sun old HotSpot JVM so that the Javascript virtual machine interprets the code in the first instance, because it can start doing it instantly. In addition, JIT compiles any code that appears to be used often enough to make it useful. It may even have different compiler optimization levels, which it slowly types. In this case, it can use several cores to interpret or run one piece of code, as well as to compile arbitrarily many others, or even when recompiling and better optimizing the same code that is executed.

However, at a technical level, static analysis can also be performed to determine when callbacks are state-dependent and allow these callbacks to run in parallel if triggering events prompt them to do so. Thus, the Javascript virtual machine can actually interpret / run the code in parallel without affecting the semantically consistent nature of the language. Such a system will be logically similar to the operation of superscalar CPUs, although at a much greater distance and with much greater complexity.