CHKPT Macro

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿

￿

￿

res￿ar￿ address

￿

￿

￿

￿

SYSnnn,

(r1)

￿

￿

￿

￿ , end address

, ￿poin￿er

￿

￿ VSE ￿ CHKPT

￿

(r2)

(r3)

￿

￿

￿

￿

dpoin￿er , filename

￿

￿

￿

￿

(r4)

(r5)

￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿

￿

￿

dcbaddress ,checkid address

￿

￿

￿

￿

,checkid leng￿h

￿

￿ MVS ￿ CHKPT

￿

,′ S′

￿

￿

￿

￿

CANCEL

￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

The MVS CHKPT macro is similar to the VSE CHKPT macro with two minor differences in the checkpoint logic. One difference is in the use of registers when control returns to you after the CHKPT macro. In VSE, register 0 indicates successful or unsuccessful checkpointing. In MVS, register 15 indicates not only successful or unsuccessful checkpointing, but also successful restart. Another difference is in the restart logic. In VSE, you specify a restart address as one of the parameters in the CHKPT macro. MVS automatically restarts with the instruction following the CHKPT macro.

Many VSE parameters are not necessary in MVS:.

The SYSnnn parameter in VSE specifies the logical unit on which the checkpoint is stored. The dcbaddress parameter of the MVS CHKPT macro gives the address of the user-coded data control block (equivalent to a DTF) for the checkpoint data set, which must be a magnetic tape or direct access volume.

A restart address is not given in MVS.

An end address used in VSE to specify the highest storage address to be dumped during CHKPT is not needed, because MVS automatically dumps the entire contents of the programs virtual storage data areas.

tpointer in VSE provides a list to the CHKPT macro of the tape files used in the program. If this parameter was not specified, repositioning of tape files would not be performed at restart. MVS automatically repositions tape files without the use of a similar parameter.

dpointer in VSE permits operator volume verification at restart time. The facility is provided by MVS when it allocates devices for a particular job step.

Filename in VSE points to the DTF describing the disk CHKPT file. This file must be opened prior to use, and label checking is performed at that time. The MVS DCB is roughly equivalent. The data set may be opened by you or by the checkpoint routine when the CHKPT macro is executed. It is recommended that the user issue the OPEN rather than default to the system, because the system opens every time a CHKPT is issued.

282VSE to OS/390 Migration Workbook

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IBM OS/390 manual Resar address, End address Poiner, VSE Chkpt, ′ S′, Chkpt 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.