VOL1

v o l u m e label

HDR1 and HDR2

data set header label

EOV1 and EOV2

data set trailer labels (end of volume)

EOF1 and EOF2

data set trailer labels (end of data set)

UHL1 - UHL8

user header labels

UTL1 - UTL8

user trailer labels

 

 

Note: UHL and UTL processing are user standard labels.

Under VSE, standard label write processing when FILABL=STD is specified in the DTF includes:

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

￿ VOL1 ￿ HDR1 ￿ TM ￿ Data Records ￿ TM ￿ EOV1 ￿ TM ￿

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

for the first and intermediate volumes of a multivolume file, and

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

￿ VOL1 ￿ HDR1 ￿ TM ￿ Data Records ￿ TM ￿ EOF1 ￿ TM ￿ TM ￿

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

for the last volume of a multivolume file.

In addition to VSE formats, OS/390 standard labels, identified by the DD parameter LABEL=(,SL), include HDR2, EOV2 and EOF2 labels. If these labels are on input tapes under VSE, they are skipped; on output tapes, they are overwritten. OS/390 accepts the absence of these labels when processing input data sets.

OS/390 obtains information about the characteristics of a tape file (for example, blocksize) from three different sources:

1.The tape label (for labelled tapes)

2.The DCB parameter of the DD job control statement (JCL) that identifies the data set

3.The DCB macro specification (assembler) or comparable high-level language file specification within the source program. (Coding these in a program is not recommended; that is, recoding and relinking of the program is required when device type, blocksizes or other data set changes are desired.)

For output tapes, specifying the file characteristics via JCL specifications is recommended. It provides flexibility by allowing OS/390 to make final device (in this case, tape drive) assignments at job execution time.

VSE file-ids can be up to 17 characters in length, and do not have to be qualified; that is, the 17 characters do not have to have any periods in the string of characters. In OS/390, file names (data set names) must have qualifiers if more than eight characters are used in the name (that is, a period must be used in the file name with no more than eight characters in a qualifier). If VSE created

file-ids are longer than eight characters and unqualified, the files can be read in

OS/390 only by specifying their file-id in apostrophes. This is done in the JCL DSN= parameter; for example, DSN= payroll/datafile52134′.

If HDR2 tape labels are not present on data sets used as input to OS/390 (HDR2s arent created by VSE systems), you must supply the

104VSE to OS/390 Migration Workbook

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Image 128
IBM OS/390 manual VOL1 HDR1 TM Data Records TM EOV1 TM, VOL1 HDR1 TM Data Records TM EOF1 TM TM, UHL1 UHL8, UTL1 UTL8

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.