You can hot-plug PCI adapter cards only if their corresponding device drivers support hot-plugging.
The LED indicators on the system often indicate the status of the slot's hot-plug operation. In the case of PCI Express devices, the LED behavior matches the behavior defined in the PCI Express specification. For other types of devices, the behavior might be platform dependent. Refer to your platform guide for specific details.
For PCI Express devices, when the Attention button is pressed, the power indicator blinks to indicate the beginning of a state transition. The blinking ends when the state transition has ended.