Normally a port will queue/buffer packets/frames awaiting transmission. If arrival rate continues to exceed transmission rate, queue/buffer overflow drops packets/frames.
Faster port to slow port is "classic" (your) example, but so too is multlple ports sending to fewer ports (e.g. 24 100 Mbps ports sending to gig port).
"does tcp slow it down ?"
Simple answer is yes, but there's much to TCP. Suggest you search Internet for additional information about TCP behavior. Your might start here: http://en.wikipedia.org/wiki/TCP_congestion_avoidance_algorithm