stolen from http://www.isi.edu/in-notes/iana/assignments/port-numbers, reformatted, corrected typos, and marked up slightly, then split into pieces, because it's not cool to make a 380KB node:
- Well Known Ports (ports 0-1023,
"on most systems can only be used by system (or root) processes or by programs executed by privileged users")
- Registered Ports (ports 1024-49151,
"on most systems can be used by ordinary user processes or programs executed by ordinary users.")
- Dynamic and/or Private Ports (ports 49152-65535)