Cb locaion address, Entrypoint

ENTRYPOINT

In VSE, it defines the storage address of the entry point of the subtask. The entry point must be in storage before the subtask can be successfully attached. The EP, EPLOC or DE parameter in MVS causes the required module to be loaded into storage (if it is not already in storage) and begins execution at the entry specified.

The entry-point name must be a member name or an alias in a directory of a partitioned data set, or it must have been specified in the IDENTIFY macro. If the specified entry point cannot be located, the new subtask is abnormally terminated. MVS requires the subtask to perform normal initialization and termination coding. Therefore, the MVS subtasks are generally separate load modules rather than interspersed coding that commonly is found in VSE subtasks.

SAVE: Defines the address of a formatted user save area for the subtask containing the general purpose (and floating point) registers while the VSE task is not active. MVS assumes the responsibility for providing areas to save registers.

ECB: Defines a task event control block used in intertask communications and task synchronization. Both operating systems use a fullword ECB, but individual bits have different meanings.

ABSAVE: Used if the subtask is to execute the main task′s abnormal termination STXIT AB routine under VSE. When an ABEND is issued in MVS for a task that has previously issued an STAE macro, the ABEND is intercepted and control is given at the STAE exit routine address.

An additional facility available under MVS is the ability to specify an end-of-task exit routine (ETXR) to be given control after the new task is normally or abnormally terminated. This is true even if the originating task was active and must be in virtual storage when required. In a sense, this facility functions something like an STXIT routine. When a termination interrupt occurs, the routine is given control. This is a useful facility that you should examine when converting the ATTACH macro.

	VSE	DETACH SAVE=savearea
			(1)

	MVS	DETACH	cb locaion address
			(1-12)

The VSE DETACH macro, issued by the main task or the subtask itself, causes the subtask to terminate. An EOJ or CANCEL macro can also perform this function.

Under MVS, the DETACH macro is used to remove the task control block of the subtask from the system and to terminate the subtask and all its subtasks. DETACH is required when either ECB or ETXR was specified in the ATTACH for this subtask. Both of these parameters signal to the initiating task that the subtask has terminated normally or abnormally. The task control blocks for all subtasks must be removed by the originating task before the originating task can

284VSE to OS/390 Migration Workbook

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.

IBM OS/390 manual Cb locaion address, Entrypoint

Models: OS/390

ENTRYPOINT