The architecture of IMS DB (Information Management System Database) consists of several key components that work together to manage and access data in a hierarchical database environment. Here's an overview of the architecture :

Database : At the core of IMS DB architecture is the hierarchical database itself. The database is organized as a tree-like structure composed of segments, with each segment representing a logical grouping of related data elements. Segments are interconnected through parent-child relationships, forming the hierarchical data model. The database stores both the data and the structure of the data, including segment definitions and relationships.

IMS Control Program (IMSCP) : The IMS Control Program is the central component responsible for managing the IMS environment. It provides various services such as database management, transaction processing, and communication with application programs. IMSCP coordinates the activities of other IMS components and ensures the integrity and availability of data.

Message Processing Region (MPR) : MPRs are runtime environments within IMS that execute application programs. These programs interact with IMS DB to perform database operations such as reading, writing, and updating data. MPRs handle communication between application programs and the IMS control program, as well as managing resources such as database buffers and locks.
Program Communication Block (PCB) : PCBs are data structures used by application programs to communicate with IMS DB. Each PCB contains information about the database segments accessed by the program, including segment names, pointers to data buffers, and status indicators. PCBs are defined and managed by application programs and are used to specify database operations and retrieve data from IMS DB.

Program Specification Block (PSB) : PSBs define the database operations that can be performed by application programs. They contain information about the PCBs used by programs, as well as the database calls and access paths required for each operation. PSBs are created and maintained separately from application programs and provide a standardized interface for accessing IMS DB.

Database Descriptor (DBD) : The Database Descriptor defines the structure of the IMS database, including segment definitions, relationships, and access paths. It serves as a blueprint for IMS DB operations and is used by IMS to validate database requests and navigate the hierarchical structure of the database.

Data Language/I (DL/I) : DL/I is a programming interface provided by IMS DB for accessing and manipulating database data. It offers a set of commands and functions that allow application programs to perform database operations such as reading, writing, and updating data. DL/I abstracts the complexity of navigating the hierarchical database structure and provides a high-level interface for interacting with IMS DB.