Reference

VSE

MVS

Method:

 

 

 

 

 

Relative Track

Assumed if DSKXTNT is

Assumed if OPTCD does not

Addressing

specified. RELTYPE=HEX

contain A. The field specified

 

(the default) requires the

by blockaddress must contain

 

hexadecimal form TTTR.

TT in binary. There is no

 

RELTYPE=DEC requires the

equivalent to RELTYPE=DEC

 

zoned decimal form

in MVS. The form must be

 

TTITTTTTRR. RR must be 00.

converted to hexadecimal.

 

 

 

Relative Block

No equivalent.

OPTCD=R must be specified

Addressing

 

in the DCB parameter. The

 

 

field specified by block-

 

 

address must contain BB in

 

 

binary. The address of the

 

 

first record is 000.

 

 

 

Actual Physical

Assumed if DSKXTNT is not

Assumed if OPTCD contains

Addressing

specified. The address must

an A. The field specified by

 

be in the form MBBCCHHR.

blockaddress must contain

 

The R must be 0. The field

MBBCCHHR. The M byte is

 

specified by KEYARG must

different in VSE and MVS.

 

contain the key of the record.

See the description of the M

 

 

byte under Track and Record

 

 

Addressing.

 

 

 

Figure 43. Record Reference by KEY in VSE and MVS

Direct Access File Processing

In VSE, parameters required for creating or processing a DAM file are supplied or made known through the DTFDA macro instruction operands and using the READ/WRITE macros. For MVS, this information is in the DSCB, DCB, and READ/WRITE macros. Some information is also supplied in optional fields of the DD statement.

Figure 44, Figure 45 on page 319, Figure 46 on page 319, Figure 47 on page 320, Figure 51 on page 325, Figure 48 on page 320, Figure 49 on page 321 and Figure 50 on page 324 show parts of VSE programs with their MVS counterparts for loading and processing DAM files.

 

OPEN

(DAMFILE,(UPDAT))

 

 

.

 

 

 

.

 

 

 

READ

DECBUPOT,DI,,,,OLDKEY,,MF=E

 

 

CHECK

DECBUPDT

 

 

.

 

 

 

.

DECBUPDT,DI,DAMFILE,′ S′ , ′ S′ , ,

 

 

READ

C

 

.

BLOCKADDR,MF=L

 

 

 

 

 

.

 

 

DAMFILE

DCB

...DSORG=DA,MACRF=(RISC,WIC),

C

 

.

...OPTCD=R,BUFL=58...

 

 

 

 

 

.

 

 

 

 

 

Figure 44.

Updating a DAM File under MVS

 

318VSE to OS/390 Migration Workbook

Page 342
Image 342
IBM OS/390 manual Dcb Dsorg=Da,Macrf=Risc,Wic, OPTCD=R,BUFL=58, Direct Access File Processing, Reference, Method

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.