When updating records, it is convenient to use the list and execute forms of READ/WRITE macros rather than the standard forms and to request dynamic buffering. To update a direct access file that was created sequentially, as in Figure 51 on page 325, use coding similar to that of the example in Figure 44 on page 318, which uses the list and execute forms of the READ and WRITE macros. The key does not need to be rewritten after a record has been retrieved and updated, so the key address field is specified as zero. You must specify BUFL because dynamic buffering was requested.

 

 

.

 

 

 

.

 

 

OPEN

DAMFILE,TAPE

 

GETTAPE

GET

TAPE

 

 

 

.

 

 

 

.

 

 

WRITE DAMFILE,ID

 

 

WAITF DAMFILE

 

 

 

.

 

 

 

.

 

 

CLOSE DAMFILE,TAPE

 

TAPE

DTFMT

 

 

 

MTMOD

 

 

DAMFILE

DTFDA BLKSIZE=50,DEVICE=3340,DSKXTNT=3,

C

 

 

ERRBYTE=ERROR,IOAREA1=OUTPUT,

C

 

 

SEEKADDR=ADDR,TYPEFLE=OUTPUT,

C

 

 

RELTYPE=HEX,VERIFY=YES,WRITEID=YES

 

 

DAMOD ERREXT=YES,RELTRK=YES

 

Figure 51. Loading a Random (Preformatted) DAM File under VSE

Multiple Search / Feedback

Under VSE, if you have specified SRCHM=YES, READ or WRITE KEY and IDLOC=xxxxxxxx, the system returns to you the address of the record currently being read or written. This address is placed in the field specified by IDLOC. VSE supplies the ID in the same form used in the SEEKADR location, except when physical IDs are involved. In that case, only the last five bytes of the physical ID, cchhr, are supplied instead of the complete relative ID including zeros.

If you use READ or WRITE ID (or READ or WRITE KEY without SRCHM), VSE returns the address of the next record. This address is placed in the field specified by IDLOC. When using relative addressing with IDLOC, all your extents, except the last extent for each file, should end on cylinder boundaries.

Under MVS, if the data set was created using relative track, key,. and extended search, you may request feedback to increase the speed of an update run. Feedback means that after the execution of a READ/WRITE macro, the address of the retrieved record is supplied by the system in the field specified by blockaddress.

Thus, if a READ requires an extended search over several tracks to locate a specific record by its key, the subsequent update WRITE may use the address supplied by the feedback option rather than repeat the entire search.

Chapter 13. A s s e m b l e r 325

Page 348 Page 350
Page 349
Image 349
IBM OS/390 manual Multiple Search / Feedback, Loading a Random Preformatted DAM File under VSE
Page 348 Page 350

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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