What is HCS (Host Compute Service) in Hyper-v server 2016?

This is a low level container management API in Hyper-V called the Host Compute Service (HCS). you can run any application without install it, all you need is import the service with it's own os runtime dependencies as package or container. Making a Windows Server Container with the HCS is just a single API call.  Making a Hyper-V Container instead just means adding a flag when calling into the API.

A layer of abstraction above the low level functionality. 

The HCS was a stable API Docker could build upon, and it was also easier to use. 

Making a Windows Server Container with the HCS is just a single API call. 

Making a Hyper-V Container instead just means adding a flag when calling into the API. 

It is os level virtualization, you can run any application without install it, all you need is import the service with it's own os runtime dependencies as package or container. The adea first invented by docker.com for Linux and Microsoft try to using it at windows. I believe it will take a while tell it become wildly used.

The Host Compute System API provides the functionality to start and control VMs and container.