Each hardware device is accessed by a single process at a time. Any multiplexing that needs to be fast is done in hardware. Other multiplexing can be done in us

Each hardware device is accessed by a single process at a time. Any multiplexing that needs to be fast is done in hardware. Other multiplexing can be done in user space. For example, and application can request a dedicated channel to some blocks on the hard disk (adjudicated by the OS) or just use another hard disk. Remember, we're building simple applications here so things don't need to constantly write off the the disk for various tasks. You would only be dealing with the disk if your actual data was too big to fit into memory. Cases like that need careful design, not delegation off to some other programmer who doesn't know your problem. If you're running a server application you split it into some reasonable number of tasks and allocate cores to them as needed. Nothing else runs on the system at all. If you need more cores either upgrade your hardware or you build another identical machine and talk to it over the network. If you look at the way Moore designs, he's crafting a complete artifact to solve a specific problem, not just throwing generic parts together.