TABLE OF CONTENTS In high-availability, mission-critical environments, it is useful (in many cases absolutely essential) to be able to swap system components while the system is running. Attempting to do this in a system that has not taken hot pluggability into account will very likely result in component damage and system disruption.
Two approaches to hot pluggability have been developed. The PCISIG invented Hot Plug for conventional PCI cards. PICMG created Hot Swap for CompactPCI. In some ways these approaches complement each other and in other ways they contrast.
Hot Plug is defined in the PCI Hot Plug Specification, Rev. 1.0, dated October 1997. The primary objective of Hot Plug is "to enable higher availability of file and application servers by standardizing key aspects of the process of removing and installing PCI adapter cards while the system is running." In an effort to expedite market acceptance of Hot Plug by making virtually any PCI card Hot Pluggable, the specification puts the burden of hardware changes on the platform vendor. Specifically, the Hot Plug environment requires that each slot have:
Power switches such that each board can be independently powered up and down.
Bus isolation switches that electrically isolate the slot from the bus while a board is being inserted or removed.
An independent RST# signal.
A way of drawing an operator's attention to a specific slot, an "attention indicator," probably an LED. There may also be a slot state indicator to show whether the slot is on...
