large enough ISA to reduce subsequent GETMAINs and FREEMAINs to zero (or some very small number). This is one of the most important things a user can do to improve the performance of a PL/I program.

15.12 PL/I and CICS

15.12.1 File Support

The only PL/I file supported by PL/I under CICS is SYSPRINT, and its usage must be limited. The functions LINENO and COUNT are supported under MVS, but give a null value if they are used under DOS. Other file access facilities are provided by CICS/VS file access macros and/or EXEC commands.

15.12.2 Statements not Supported

DISPLAY and DELAY are not supported. The functions PLIREST, PLICANC,

PLICKPT and PLISRTx are not supported. MULTITASKING is not supported.

Inter-language linkages are limited to Assembler (with some restrictions).

15.12.3 CALLing DUMP

The only options permitted in calling DUMP are T and NT, S and C, B and NB, K and NK. The dump is not written to the PLIDUMP file, but is sent by transient files to a destination of CPLD. K and NK are special CICS/VS-only options on

PLIDUMP.

15.12.4 Execution Options

The execution options can only be communicated to PL/I by means of a PLIXOPT string:

DCL PLIXOPT CHAR(nn) VAR EXT INIT(′ xuxuxx′ ) ;

The options permitted are COUNT and NOCOUNT, FLOW and NOFLOW, ISASIZE, REPORT and NOREPORT, STAE and NOSTAE. The option SPIE will be ignored if it is specified. If a PLIXOPT string is not specified, defaults will be supplied. If they are wrong, the mistake can be very costly in CICS/VS transaction execution time. Every PL/I-CICS/VS transaction program should have a PLIXOPT string, especially to set ISASIZE. Note that the STAE option causes PL/I to issue a CICS DFHPC SETEXIT macro. It uses CICS error handling. It does not override it.

15.12.5 Compatibility

All these restrictions already exist in DOS. No differences exist at the PL/I level. The compatibility of CICS transactions written in PL/I appears therefore to be total.

15.12.6 PL/I-CICS/VS Transaction ABEND Codes

These are documented in the PL/I Programmer¢s Guide, not the CICS manuals. The only one which tends to puzzle users is ²APLS², which means that the PL/I ERROR condition was raised, but not by a program check or a transaction abend. For example, CONVERSION might have been raised by the PL/I library.

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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.
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