13.2.6.4 I/O Error Checking

When an input/output error occurs under MVS, a user-written synchronous error routine (SYNAD) can be given control. You can use this routine to analyze exceptional conditions or uncorrectable errors. The error can be skipped or accepted, or processing can be terminated.

If an input/output error occurs during data transmission, standard error recovery procedures, provided by the operating system, attempt to correct the error before returning control to your program. An uncorrectable error usually causes an abnormal termination of the task. However, if you specify in the DCB macro the address of an error analysis routine, the routine receives control in the event of an uncorrectable error.

You can write an SYNAD routine to determine the cause and type of error that occurred by examining:

∙

∙

∙

∙

The contents of the general registers.

The data event control block.

The exceptional conditional code.

The standard status and sense indicators.

Use a special macro instruction, SYNADAF, to perform these functions automatically. SYNADAF produces a descriptive error message that can be printed by a subsequent PUT or WRITE macro.

Having completed the analysis, you can return control to the operating system or close the erroneous data set and terminate processing. In no case can you attempt to reread or rewrite the record because the system has already attempted to recover from the error.

When you use GET/PUT macro instructions to process a sequential data set, the operating system provides three automatic error options (EROPT) to be used if there is no SYNAD routine, or if you want to return control to your program from the SYNAD routine:

∙

∙

∙

ACC - accept the erroneous block. SKP - skip the erroneous block.

ABE - abnormally terminate the task.

These options are applicable only to data errors, because control errors result in abnormal termination of the task. Data errors affect only the validity of a block of data. Control errors affect information or operations necessary for continued processing of the data set. These options are not applicable to output errors, except printer output errors. When chained scheduling is used, the SKP option is not available. If it is coded, it defaults to the ACC option. If you do not complete the EROPT and SYNAD fields, the system assumes ABE.

13.2.6.5 LIOCS Card File Definition

The methods of processing cards files are the same in VSE and MVS. Figure 31 on page 295 compares the VSE DTFCD and the MVS DCB operands. Figure 32 on page 295 gives an example of the macros that process a card file under both operating systems. Figure 33 on page 296 shows a short sample program.

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IBM OS/390 manual 13.2.6.4 I/O Error Checking, Liocs Card File Definition
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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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