PCI-E was hot pluggable since day 1, usually you have some extra bits and pieces to make it reliable though - depending on server it might involve switches or s

PCI-E was hot pluggable since day 1, usually you have some extra bits and pieces to make it reliable though - depending on server it might involve switches or special card holders in case or card cages which you put the card in first. And usually some status leds and "attention, I want to remove this device" button. A card cage design was used on some IBM machines, where you attach the card a slim sled with a lever attached, this allowed you to "slide in" the card into running computer then use the lever to push it into edge connector (this also handled powering up/down the connector, iirc). Some servers have cases which instead implement that completely in the case itself, though usually that means you need more effort to do the replacement. Then there are alternative PCI-E connectors - ExpressCard, U.2 & SATAExpress (used in SSDs), OcuLink and related (cabled PCI-E)