(from ACF/SSP) and user-written VTAM exits. In our example STEPLIB points to the ACF/SSP library which contains the NCP loader. Any libraries defined by STEPLIB are PDSs containing load modules, and have similar DCB characteristics to SYS1.LINKLIB.

4VTAMLIB contains VTAM tables which are assembled and linked, such as the subarea Class of Service table and the various mode tables. Again, VTAMLIB is a load module PDS with DCB=(RECFM=U) and an appropriate block size. In our example four libraries are concatenated together; the IBM-supplied VTAM tables are in SYS1.VTAMLIB and any user-defined replacements are in the two other libraries defined in front of SYS1.VTAMLIB.

5VTAMLST contains VTAM tables which are not assembled and linked. Here reside the definitions of the VTAM resources (major nodes), the NCP source deck, VTAM start options and those tables which VTAM reads in source form. VTAMLST is a PDS with DCB=(RECFM=FB,LRECL=80) and a suitable block size. In the example three VTAMLST data sets are concatenated together; all the VTAM definitions are in these libraries and SYS1.VTAMLST is not used.

6The NCPLOAD DD statement points to the data set(s) where NCP load modules may be found. The DD name for this statement is user-defined, and VTAM discovers it from the NCP source definitions (BUILD LOADLIB=).

7In addition, VTAM requires a member IVTPRM00 to be present in the SYS1.PARMLIB OS/390 data set. This member provides initialization parameters for Communication Storage Manager (CSM), which is part of VTAM from V4R4 onwards. CSM provides data storage facilities for both VTAM and TCP/IP, as part of the high-performance data transfer function implemented by those products on high-speed connections.

//NET

PROC

PERF=13

 

//NET

EXEC

PGM=ISTINM01,REGION=6000K,TIME=1440,DPRTY=(15,13),

C

//PERFORM=&PERF

//STEPLIB DD DSN=SSP.V4R6.SSPLIB,DISP=SHR //VTAMLIB DD DSN=SA39.VTAMLIB,DISP=SHR

//DD DSN=ITSC.VTAMLIB,DISP=SHR

//DD DSN=SYS1.VTAMLIB,DISP=SHR

//DD DSN=SYS1.NETVIEW.V3R1M0.SCNMLNK1,DISP=SHR

//VTAMLST DD DSN=ITSC.VTAMLST,DISP=SHR

//DD DSN=BUCZAK.VTAMLST,DISP=SHR

//DD DSN=RISC.VTAMLST,DISP=SHR

//SISTCLIB DD DSN=SYS1.SISTCLIB,DISP=SHR //NCPLOAD DD DSN=ITSC.NCPLOAD,DISP=SHR

//DD DSN=RISC.NCPLOAD,DISP=SHR

Figure 17. VTAM Start Procedure

9.1.2 Resource Definition and Operation

The differences in the coding of VTAM definitions, tables and start options are minor, but cannot be ignored. The VTAM Resource Definition Reference and the VTAM Network Implementation Guide should be used to review operating system differences.

Chapter 9. Telecommunications Subsystems 187

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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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