As far as I know, some cables should not be disconnected from computer while it and/or the device is running and persistent hardware damage can occur if they are unplugged errorneously.
Currently the table is like this:
- USB, Firewire, Ethernet, HDMI – can connect and disconnect without caution;
- VGA Monitor – OK;
- Serial port (COM) – OK probably;
- SATA – should be more or less OK;
- IDE, PS/2 – not recommended;
- Parallel port (LPT) – very not recommended;
- CPU, RAM, PCI, motherboard to PSU slot, … – I don't know.
I tried or seen hot disconnections for all mentioned above (expect of LPT and the last point) without any problems.
Why the slow or device can be damaged by sudden disconnection? What happens when some (not all) pins are not connected?
Does it still apply for ( LPT or PS/2 or IDE ) USB adapters? Can they also be damaged or "unplugged cable => burned port" is only for old legacy hardware?
Can a cable with damaged wires (but without any short circuits) damage the port or device?
Note: just software issues (data loss, operating system crash) is out of scope in this question. It's only about hardware failures that cannot be fixed without bying things.
Best Answer
I think it is threefold:
When power supply of various IC's is not connected before signals on other pins, the semiconductor can act as a thyristor between power supply rails, which results in short circuit the PSU (failing the whole PC) and high power dissipation or blowing the chip(s on the device).
The computer for many devices just isn't aware of them being plugged or unplugged. The operating system will not be able to use it as it is unaware of its existence OR the operating system is trying to use a device that is no longer available. Only few buses are able to cope with hot plugging (eg. USB).
(inductive) power surges due to unplugging can easily blow poorly designed hardware. I blew out the DAC's on my video processor once...