Close Macro, Reread Leave Rewind Disp | IBM OS/390 specification

Note: You can specify any number of dcbaddresses and associated options in the OPEN macro instruction.

CLOSE Macro

VSE	CLOSE(R)	filename
		,...
		(r1)

MVS	CLOSE	dcbaddress
		,option ,... ,TYPE=T
		(2-12)

1. Options

REREAD

LEAVE

REWIND

DISP

2. If you omit the option, the following positioning occurs:

If TYPE=T is coded, LEAVE is assumed (BSAM only).

If TYPE=T is not coded, DISP Is assumed (BSAM only).

3.You can code CLOSE with TYPE=T to temporarily close sequential data sets on magnetic tape volumes processed with BSAM. When you use TYPE=T,

the DCB used to process the data set maintains its open status, and you don′t have to issue another OPEN macro to continue processing the same

data set. A request to temporarily close a data set causes MVS to process labels, modify some of the fields in the system control blocks for that data set, and reposition the volume (or current volume in the case of multivolume data sets) in much the same way that the normal CLOSE macro does. When you code TYPE=T, you can specify that the volume either be positioned at the end of data (the LEAVE option) or be repositioned at the beginning of data (the REREAD option). Magnetic tape volumes are repositioned either immediately before the first data record or immediately after the last data record; the presence of tape labels has no effect on repositioning. When a DCB is shared among multiple tasks, the task that opened the data set must also close it; however, a subtask of the task that opened the DCB can issue the CLOSE macro with the TYPE=T option.

4.When using QSAM, close all output data sets before ending the program to ensure that all records have been written.

CNTRL Macro

VSE	CNTRL	filename	,code
		(1)

MVS	CNTRL	dcbaddress,code ,number of blocks

298VSE to OS/390 Migration Workbook

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.

IBM OS/390 manual Close Macro, Reread Leave Rewind Disp

Models: OS/390