When I started using Unix in the mid-90s, RAM was still expensive, and the rule thumb was that to get best use of a workstation you should have 2x main memory as swap, 4x for a server. This was reckoned to give the best trade-off between the number of processes running and the working set you actually needed.

Shortly afterwards this stopped making sense because RAM got cheap. Should a 4G PC have a 16G swapfile? Should a 256G server have a 1T swapfile?

In short virtual memory was a hack to get around economical constraints. If you have the main memory, use it! Were it not baked into the OS at a deep level, I've have stopped using swap 10 years ago. It could be taken out of the next version of all the main OSs altogether, and no-one would even notice.

I didn't actually mean to add that second link in there (I realised you were talking about virtual machines and edited my comment accordingly... But forgot to remove the second URL!)

However, disk-backed page faults are but one component of a virtual memory subsystem. The real genius is the OS can provide access to memory uniformly in a way that is transparent to processes.

Indeed but in practice, paging to disk and memory protection are so entwined now.

Not really. In Windows its just a change to a system setting to disable the swap file, and in a unix it's a config file change or a command like swapoff to turn it off.

The fact that the two are entwined now is because of system defaults and decisions by OS developers on how to implement the page replacement algorithms in MM subsystems.

swapoff -a

Bitter experience has taught me to have a swapfile 1x main memory and set swappiness=0 in the kernel.