VSE DTFDA

MVS DCB DSORG=DA

BLKSIZE = nnnn

BLKSIZE = nnnn

DEVICE = nnnn

UNIT = (in DD statement)

ERRBYTE = xxxxxxxx

(See description of SYNAD routine)

IOAREA1 = xxxxxxxx

Area address (READ/WRITE macro)

SEEKADR = xxxxxxxx

Not required (READ/WRITE macro)

TYPEFLE = xxxxxx

OPEN macro option

AFTER = YES

MACRF = (..WA..)

DEVADDR = SYSnnn

UNIT = (in DD statement)

ERREXT = YES

SYNAD = xxxxxxxx

HOLD = YES

This function can be implemented by using

 

the ENQ/DEQ logic of MVS for a specific

 

resource or by requesting exclusive con-

 

trol of a data block thru MACRF = (..X..)

IDLOC = xxxxxxxx

(See description of updating the file)

KEYARG = xxxxxx

Keyaddress (READ/WRITE macro)

KEYLEN = nnn

KEYLEN = nnn

LABADDR = xxxxxxxx

EXLST = xxxxxxxx

READID = YES

MACRF = (..RI..)

READKEY = YES

MACRF = (..RK..)

WRITEID= YES

MACRF = (..WI..)

WRITEKY = YES

MACRF = (..WK..)

RECFORM= xxxxxx

RECFM = xxx

RECSIZE = (nn)

Length (READ/WRITE macro)

 

or DCB LRECL = nnnnn

RELTYPE = xxx

OPTCD = (...,R...).No equivalent for DEC

SEPASMB = YES

User must code the DCB

SRCHM = YES

LIMCT= n,OPTCD = E

TRLBL = YES

EXLST = xxxxxxxx

VERIFY = YES

OPTCD = W

XTNTXIT = xxxxxxxx

EXLST= xxxxxxxx

Figure 40. Comparison of DTFDA and DCB Macros

Error Bytes

The error bytes used in VSE to test for successful completion of an I/O operation are equivalent to a two-byte exception code in MVS. The two-byte exception code is placed in the DECB (DECB+1) of the corresponding READ/WRITE macro after a WAIT or CHECK macro has been issued.

If you issue a WAIT macro (WAITF in VSE), test for successful I/O completion provide the appropriate actions.

In MVS, if you issue the CHECK macro, the system performs the test. If an unusual condition occurs, the system branches to your SYSNAD routine if you have provided one, or it abnormally terminates the job step.

The information provided in the two bytes is different in VSE and MVS. Therefore change any parts of your programs that refer to these error bytes. Figure 41 on page 313 gives a comparison of the VSE and MVS exception codes.

312VSE to OS/390 Migration Workbook

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IBM OS/390 After = YES, Errext = YES, Readid = YES, Readkey = YES, Writeid= Yes, Writeky = YES, Srchm = YES, Trlbl = YES
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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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