Node.js uses non-blocking IO to achieve massive amounts of concurrency on a single thread, while one-thread-per-request models such as PHP rely on OS threading to do the exact same thing.
If anything, the node.js model is often capable of more concurrency because of the inefficiencies involved in OS threading and context switching.
EDIT: of course, event driven PHP exist. I don't know much about the current state of it.
Node.js uses non-blocking IO to achieve massive amounts of concurrency on a single thread, while one-thread-per-request models such as PHP rely on OS threading to do the exact same thing.
If anything, the node.js model is often capable of more concurrency because of the inefficiencies involved in OS threading and context switching.
EDIT: of course, event driven PHP exist. I don't know much about the current state of it.