MSGLEN=length - The length of the MSGAREA specified above. The size of a message is 128 bytes.

O P T C D = (

￿ASY - Asynchronous access; VSAM returns control to the program after scheduling the request so the program can do other processing while the request is earned out. SYN is the default and specifies that VSAM will return to the processing program when the request is complete.

￿WAITX - If ²OPTCD=(..,SYN..)² and the specifics ²MACRF=(..,LSR or GSR..)², and ²EXLST ...,UPAD=², then VSAM branches to the UPAD

routine address when VSAM would otherwise have issued a WAIT. The most common use of UPAD routines is by IMS/VS or it may be used as a replacement for the VSE VSAM EXCPAD routines.

13.2.5.4 SHOWCB Macro

The VSE VSAM SHOWCB macro may not be source compatible depending on the fields requested. The use of the macro and the results should be carefully examined.

MVS VSAM Additional SHOWCB Fields

BFRFND - Number of successful GETs without physical reads required. (LSR or GSR only)

BUFRDS - Number of GETs requiring physical reads. (LSR or GSR only)

ENDRBA - Ending RBA of the space used by the data or index components (that is, the last byte used in the component).

HALCRBA - The High-Allocated-RBA of the specified component.

NUIV - Number of physical WRITEs not issued by the user. (LSR or GSR only)

UIW - Number of WRITEs issued by the user. (LSR or GSR only)

13.2.5.5 MVS VSAM CHECK Macro

The MVS VSAM CHECK macro is used to suspend processing until VSAM has completed the request associated with the RPL. This macro is used for asynchronous processing (that is, OPTCD=(ASY..).

13.2.5.6 VSE VSAM TCLOSE Macro

The TCLOSE macro of VSE is coded in MVS: ²CLOSE ...,TYPE=T²

13.2.5.7 VSAM Error and Reason Code Compatibility

MVS VSAM error codes and reason codes may have a slightly different meaning than VSE VSAM. In all cases, MVS documentation should be consulted. Especially in Assembler, the logic for specific error codes should be verified. In some cases, MVS VSAM provides additional information.

13.2.6 Data Management Macros

This section compares the VSE and MVS data management macro instructions. Detailed information on the coding of MVS data management macro operands can be found in the publication DFSMS/MVS Macro Instructions For Data Sets, SC26-4913.

Note: As a VSE user, you are familiar with the term filename. In MVS, filename is referred to as dcbaddress.

292VSE to OS/390 Migration Workbook

Page 316
Image 316
IBM OS/390 manual Data Management Macros, Showcb Macro, MVS Vsam Check Macro, VSE Vsam Tclose Macro

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.