difference between mysql_connect() and mysql_pconnect()?

When mysql_pconnect() is used, the function initially tries to find an open persistent connection. If found; the identifier is returned. In this case, a new connection is not established. On the other hand, when mysql_connect() is used, a new connection is established.
Using mysql_pconnect(), the connection is not closed to enable future use.
Example:
mysql_pconnect("localhost","mysql_user","mysql_pwd");