In IMS (Information Management System), control blocks are data structures used by various components of IMS to manage and control system operations, resource allocation, and communication between different parts of the system. These control blocks play a crucial role in coordinating the execution of IMS transactions, managing database access, and maintaining system integrity. Some of the key control blocks used in IMS include:
* Program Communication Block (PCB) : PCBs are used by application programs to communicate with IMS and access database resources. They contain information about the database segments that an application program intends to access or manipulate, along with other parameters required for database operations.
* Program Specification Block (PSB) : PSBs define the database operations that application programs can perform. They specify the segments to be accessed, the access paths to be used, and the Program Communication Blocks (PCBs) associated with each database operation.
* Message Control Block (MCB) : MCBs are used for message routing and control within IMS. They contain information about the source and destination of messages, message priorities, and other message-related parameters.
* Transaction Control Block (TCB) : TCBs manage the execution of IMS transactions. They contain information about the state of transactions, transaction identifiers, transaction attributes, and other transaction-related parameters.
* Database Descriptor (DBD) : The DBD defines the structure and characteristics of IMS databases. It contains metadata about database segments, segment attributes, relationships, access paths, and other database-related parameters.
* Database Descriptor Control Block (DBDCB) : DBDCBs are used to manage access to IMS databases. They contain information about database buffers, database locks, and other database access parameters.
* Data Communication Block (DCB) : DCBs are used for communication between IMS and external systems. They contain information about communication protocols, data formats, and other communication-related parameters.
* Task Control Block (TCB) : TCBs manage the execution of tasks within IMS. They contain information about task states, task priorities, task identifiers, and other task-related parameters.
These are some of the main control blocks used in IMS to manage system operations, resource allocation, and communication. Each control block serves a specific purpose and plays a crucial role in the overall functioning of the IMS system.
