Here’s some fairly good background talking exactly about what you’re asking: java and multiple cores.
Long story short, you should expect that you can run multiple servers without any additional software or configuration. If you decide to get a hypervisor–or if you look into CPU pinning/affinity–that’s always an option, but I think it’s overengineering a solution for what is otherwise a very straightforward scenario.
MineOS doesn’t do resource-use accounting, and so most users typically are just interested in ‘getting it working’.
If you want something that divvies up the resources, you’re also divvying up the userspace, which means multiple installations of MineOS because MineOS isn’t going to know how to create additional servers on separate instances.
Ultimately this means that hypervisor overhead + redundant installations might have a more detrimental impact than simply letting Java delegate the work of your servers to the appropriate cores.
Last thing of note, yes there are additional servers that take advantage of multiple processes, but even without, Java itself can use more than a single core from the host machine.
- garbage collection can be done separately from the game loop
- games can be done on separate cores as well