Does this only apply to only the PS/2 ports… or all the different ports (Parallel, Serial)? I know with USB you can plug that in and out with no problem. What is different with that? Is it not still a live feed of electricity?
and PM Blair is the bomb!!! ....jk
This is a complicated one but if you really want to know, I'll tell you.....
Technically, serial (RS232) & parallel ports are not powered.
However, there are some parallel/serial devices which need power but do not come with their own power source. Serial mice, for example, need a small amount of power for the circuitry thats inside them. Also, dongles require a small amount of power but they do not have batteries or external power packs either. Serial Mice etc draw their power from the port by using the output signal (data) lines in the port. As serial ports were originally intended for communication between 2 devices (e.g between 2 computers), there are 3 output signal lines in a serial port (TD, RTS & DTS). Signals sent from the port represent 1/0 or ON/OFF (think of binary). This form of signal is represented by voltages, e.g zero or negative voltage = OFF, 3V & above = ON.
Devices such as serial mice are able to use these signal line to acquire the power they need to drive their own circuitry. Obviously devices which need more power than this (eg printers), must have their own power source instead of taking power from the port.
USB ports are metal & are powered and USB devices may be plugged in & out of live ports (hot swappable), as you said. The reason this is safe is due to the design of the USB connectors themselves. They are designed with the outer metal sheath to be more prominent than the internal connectors. This means that the outer sheath always make contact with the port first. As this outer sheath provides the 'ground' connection, this means that the resulting circuit is already grounded (or earthed) when the live parts come in contact. This eliminates the risk of static electricity damaging any components on the board or in the USB device.