As you will note in Figure 1, after a TSO user enters a BDT request, it is processed by the BDT command processor, BDTTSO. BDTTSO issues an SVC to route it to IGX00034. This module invokes the BDT language processor (BDTLP), building the first control block, called the BDT subsystem interface data area (BSID), which contains the user’s request. The BSID is then passed to BDTSSBDT by the subsystem interface (SSI).