Sequential DASD files are compatible between VSE and OS/390. However, OS/390 does not support sequential (SAM) files located within VSAM managed space. These files will have to be reloaded to different DASD areas before OS/390 can process them.

DL/I databases are compatible with IMS databases 1 if the ²IMSCOMP² parameter was specified during the DL/I DBD generation. If this parameter was not specified, then reloading of the database will be necessary; that is, a VSE positioning activity. Similarly, DB2 for OS/390 provides compatibility with DB2 for VSE. A section on database differences is included in this publication.

Note: VSE DASD volumes can be read and processed by OS/390. VSE DASD volumes, when first read by an OS/390 system, will have their free space areas calculated and appropriate entries recorded in the volume¢s VTOC. VSE systems can later process these volumes as required. (Even though OS/390 has written new records in the VTOC, VSE will ignore them.) Never, however, should both systems have concurrent access to DASD volumes. Also, all volumes are required by OS/390 to have unique volume serial numbers.

2.1.2.4 Operations

OS/390 operational procedures and operator commands differ significantly from those used in VSE. The input/output spooling subsystems (VSE/POWER and OS/390 JES) are quite different in function and operations also. Some of these differences are addressed in this publication.

Changing operational procedures and training of operators in the operations of OS/390 are very important tasks that must be performed during a VSE to OS/390 migration. Training courses are available to assist in this effort.

2.1.3 Comparison of Basic VSE Functions & Components to OS/390

Here is a list of some of the areas or programs that may be affected:

Table 1 (Page 1 of 3). Comparison of VSE Functions & Components to OS/390

Replacements

VSE

OS/390

Comment and Reference

 

 

 

VSE Base Functions

OS/390 Base Functions

 

IOCP

IOCP, HCD *

 

POWER (w/PNET, RJE)

JES2, JES3 (w/NJE, RJE) *

 

EREP

EREP *

 

MSHP

SMP/E *

 

...

...

 

 

 

 

Application Generators

Application Generators

 

VisualAge

VisualAge

 

VisualLift

VisualLift *

 

SDF/CICS & SDF II

SDF II

 

CSP

CSP

 

DMS/CICS

DMS/CICS

 

 

 

 

1IMS databases are the OS/390 equivalent of VSE DL/I databases.

16VSE to OS/390 Migration Workbook

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IBM manual Comparison of Basic VSE Functions & Components to OS/390, Operations, Iocp IOCP, HCD, Erep Mshp SMP/E
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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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