DBMS_OUTPUT has different default buffer sizes, depending on your Oracle version.
You can increase the buffer up to 1,000,000 using the following PL/SQL statement:
The SQL*Plus statement to achieve the same result is:
SET SERVEROUTPUT ON SIZE 1000000
Starting with Oracle release 10g, it is possible to use the following unlimited buffer settings:
DBMS_OUTPUT.ENABLE (buffer_size => NULL);