0 - 2 of 2 tags for multiple sessions

Hi can any one explain me how SESSION command is working in teradata;
Assume that i have 18 PE's in my teradata system. Will it login to 13 PE's at the same time. Please coreect me if i am wrong.
How to calculate No of sessions in teradata & what are the things we need to consider for sessions.

This book provides information about Teradata Parallel Data Pump (TPump), a data loading utility that helps you maintain (update, delete, insert, and atomic upsert) the data in your Teradata Database. TPump uses standard Teradata SQL to achieve moderate to high data-loading rates.