new to electronics. I am not quite sure I understand hot-swapping fully. It appears that hot-swapping is when you could replace a device while the system is operating without interruptions; however, how would you replace a device that needs to always constantly be turned ON if it turns off it would interrupt the system?
Seems impossible.
It doesn't mean that there won't be any interruptions, it just means that the device will not be damaged and can resume normal operation after a hot plug/unplug event.
SATA hard disks are a good example of this: If you unplug the disk while the computer is running, you of course won't be able to access the disk anymore. Similarly, you will only be able to access a disk once you've actually plugged it in. "Hot swappable" only means that you don't have to shut down the entire computer in order to swap a disk. (Of course, you'll have to tell the operating system that you're about to unplug the disk, otherwise you might lose some data that was not yet written by the OS. You'd typically do this by unmounting the drive. This is what "safe remove" does in Windows.)
Imagine having to reboot your computer every time you want to plug in or remove an USB device - that'd be super annoying. That's why USB devices must be hot pluggable.
'Hot-swappable' is a combination of both hardware and software that allows you to connect and remove devices without powering the machine down, without damaging them or losing data, and use them once connected.
The hardware part typically consists of making the connector pins connect in a specific order, usually first ground, then power, then data. Additionally careful design of the device interface is required to limit inrush currents, so that plugging the device in doesn't cause a large voltage dip on the host system.
The software part requires that the host machine can see the new device, and initialise its driver, without requiring a power cycle. This isn't difficult, but has to be designed for. In the bad old days, machines would enumerate attached devices at powerup, and a device arriving later could not be accommodated. It may also need an orderly shutdown of the device before it can be removed, flushing buffers to permanent storage for instance.
