[spion]

Not magic, but APIs like these: https://en.wikipedia.org/wiki/Epoll https://en.wikipedia.org/wiki/Kqueue

Pretty much all event loop based programs work the same way: instead of blocking on a single request for IO, they use system calls (e.g. epool_wait) that block until any of the many descriptors (sockets) has some event (data to be read, client connecting, etc). It gets a bit complicated when there are queued tasks for the thread pool and timers involved too, but its the same principle.

[wppick]

Don't most computer have separate processors for network, hard drive, etc. So, even if you have a single core processor, you are still running a multi-processor environment? Can anyone give me details on this? Someone told me something like this once and it has confused me ever since...

[irascible]

Yes. There are 100s of sub units that are complete processors on your motherboard. DSP, Ethernet controllers, Disk IO controllers, sound controllers, memory controllers.. and thats not counting the programmable controllers in every disk drive, sd card, reader, USB hub, peripheral, etc.

[wppick]

Does this have an impact on writing concurrent software?