OPEN

TAPE

 

VSE

PUT

TAPE

 

 

.

 

 

 

CLOSE TAPE

 

RECORD1

DS

2000C

 

TAPE

DTFMT DEVADDR=SYS005,TYPEFLE=OUTPUT,

C

 

 

FILABL=STD,IOAREA1=RECORD1,

C

 

 

HDRINFO=YES,IOREG=(5),

C

 

 

RECFORM=FIXBLK,BLKSIZE=2000,

C

 

 

RECSIZE=100,REWIND=NORWD

 

 

MTMOD RECFORM=FIXBLK

 

 

OPEN

(TAPE,(OUTPUT,LEAVE))

 

 

LA

5,RECORD1

 

MVS

PUT

TAPE,(5)

 

 

.

 

 

 

CLOSE (TAPE,(LEAVE))

 

RECORD1

DS

CL100

 

TAPE

DCB

DDNAME=TAPEDD,DSORG=PS,MACRF=(PM),

C

 

 

RECFM=FB,BLKSIZE=2000,LRECL=100

 

 

 

 

Figure 36.

Tape File Programs in VSE and MVS

 

13.2.6.8 LIOCS Device-independent File Definition

Under VSE, when using the DTFDI macro to define your file, your entire program should be device-independent. Under MVS, every program should also be device-independent for optimum use from the operating system. In revising a VSE program with a DTFDI to run under MVS:

Code RECFM=F in the MVS DCB macro. DTFDI does not need the RECFORM parameter because only fixed, unblocked records are supported. If you omit RECFM in MVS, undefined is assumed.

If the DTFDI specified DEVADDR=SYSLST or DEVADDR=SYSPCH, the MVS DCB must specify RECFM=FM because the first byte of the VSE output area contains a control character. For increased flexibility, supply the RECFM and DEVADDR parameters, and all other parameters describing data set characteristics in the DD statement instead of in the problem program.

Figure 37 on page 304 shows a comparison between the VSE DTFDI and the MVS DCB macros.

Chapter 13. A s s e m b l e r 303

Page 327
Image 327
IBM OS/390 manual Liocs Device-independent File Definition, Open Tape VSE PUT Close Tape, Close TAPE,LEAVE

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.