[purplefox]

Yes, I meant threads ;) E.g. A web server using node.js on a 32 core server. You would have to manually manage 32 instances of node, and use a load balancer or the cluster module in order to route requests to the instances. With vert.x you just start one instance and from the command line you tell it how many instances to start. It then scales over your cores, no glue code or cluster module to write. (There's an example of this on the front page of the website).

[mbq]

Having VM per core may be quite beneficial -- you get more fault tolerance, immunity to GC glitches and one tier less when scaling over several machines. And there are nice tools to manage multiple processes.