MARC is a Transaction Server transaction processor that enables you to perform system operations and tasking functions. You initiate communications with MARC by opening the MARC window. Depending on the way your terminal is defined to the Transaction Server, the MARC window might appear automatically after you log on to the Transaction Server. If it does not, you might still be able to open the MARC window by entering the command ?ON MARC. Your interactions with MARC between the time you open the MARC window and the time you log off or close the window are referred to as a session. MARC assigns each session an identifying number called the session number.