13.2.6.1 List and Execute Macro Forms

The list and execute forms of data management macro instructions, used together provide the same services available from the standard form of the macro. The list form of the macro provides a parameter list to be passed to either the control program or another problem program, depending on the micro instruction.

Use the execute form with one or two parameter lists established by the list form. The execute form provides the executable instructions required to modify the parameter lists and pass control to the required program. The advantages of the list and execute forms of a macro are:

Any operands that remain constant in every use of the macro can be coded in the list form. You can omit these operands in each of the execute forms of the macro that uses the list. This saves coding time and virtual storage area when you use a macro many times.

The execute form of the macro can modify any of the operands previously designated. There are some exceptions.

The list used by the execute form of the macro can be located in a portion of virtual storage assigned to the task through the use of the GETMAIN macro. This ensures that the program remains reentrant.

13.2.6.2 Definition of BLKSIZE

In VSE, the keyword BLKSIZE is defined as the length of one input/output area. The value specified in BLKSIZE depends on the type of processing intended. Depending on the selected options in the DTF, the value specified in BLKSIZE for the VSE file can be:

Data length (for direct access and all sequential files)

Data length, plus key length (for direct access files)

Data length, plus eight bytes for count (for direct access and sequential DASD files)

Data length, plus count, plus key length (for direct access files). In all cases MVS uses the keyword BLKSIZE to mean only data length.

Note: In MVS, the maximum value for BLKSIZE (that is, length of data blocks) is 32760. In VSE, the length of data blocks on DASD or tape can be greater than 32760.

13.2.6.3 IOREG

In VSE, specification of the IOREG parameter on a DTF allows blocked records to be processed directly in the buffer. In MVS, the equivalent technique is called Locate Mode. There are two major differences between IOREG and Locate Mode:

Locate Mode always returns the record address in R1; consequently, an LR ioreg,R1 instruction must be inserted after each GET instruction when converting to MVS.

The combination IOREG=(reg),TYPEFLE=OUTPUT has no exact equivalent in MVS. The easiest way to convert this type of file is to use Move Mode (MACRF=PM) instead of Locate Mode (MACRF=PL).

Chapter 13. A s s e m b l e r 293

Page 317
Image 317
IBM OS/390 manual List and Execute Macro Forms, Definition of Blksize, Ioreg

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.