In MVS, to make a request for feedback, insert the letter F in the type code of a READ/WRITE macro (DIF, DAF and so on). The format of the blockaddress field after feedback, however, is determined by the OPTCD parameter. If the OPTCD parameter does not contain an F, feedback will be in the form of MBBCCHHR. If you code an F in the OPTCD parameter, the format of the feedback depends on the reference method used. Figure 52 provides details on reference methods and feedback formats.

Type or

 

 

 

 

 

Reference

 

 

 

 

 

 

 

 

 

 

 

Character-

 

Relative

Relative

Relative

Actual

istics

 

block

track

track

device

 

 

number

number

number.

address.

 

 

within the

and block

You supply

 

 

 

data set.

identifi-

key in key

 

 

 

You supply

cation.

field.

 

 

 

key

 

 

 

 

 

 

 

 

 

 

 

BBB

TTR

TT

MBBCCHHR

 

 

 

 

 

 

Feedback

Feedback

Binary

T T = T r a c k

Relative

 

Format

Format

value left

number

track

 

 

 

justified in

(2-byte

number

 

 

 

block

binary

(2-byte

 

 

 

address

value)

binary

 

 

 

field.

 

value)

 

 

 

 

R = R e c o r d

 

 

 

 

 

on track

 

 

 

 

 

(1-byte

 

 

 

 

 

binary

 

 

 

 

 

value)

 

 

 

 

 

 

 

 

Minimum

3

3

2

8

 

length

 

 

 

 

 

(bytes) of

 

 

 

 

 

Block-

 

 

 

 

 

address

 

 

 

 

 

field

 

 

 

 

 

 

 

 

 

 

 

OPTCD

Relative

BBB

BBB

TTR

TTR

= F

Address

3

3

8

3

 

Bytes

 

 

 

 

 

 

 

 

 

 

 

OPTCD

Actual

MBBCCHHR

MBBCCHHR

MBBCCHHR

 

NOT

Address

8

8

8

 

= F

Bytes

 

 

 

 

 

 

 

 

 

 

 

Figure 52. MVS Feedback Formats

13.2.6.13 LIOCS Indexed Sequential Definition

Indexed sequential (ISAM) files should be converted to VSAM; that is, ISAM files should not be used in MVS. VSE ISAM files should either be converted prior to the migration to MVS (recommended) or during the conversion process.

326VSE to OS/390 Migration Workbook

Page 349 Page 351
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IBM OS/390 manual Liocs Indexed Sequential Definition, Type or Reference
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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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