Data Managememt Under MVS Operating System - IBM Mainframe

Managing data simply refers to identifying, organizing, storing, and cataloging information so that it can be easily accessed and retrieved. DFP, or Data Facility Product, working in conjunction with the MVS operating system, manages and accesses data stored on disk and tape devices - relieving the user from manual interference.

In order to manage data retrieval from the various auxiliary devices, DFP relies on a retrieval method called access method. An access method enables a program to access data in a data set. An access method is determined by the way a particular data set is organized and stored and how such organization is reflected in the code of the source program. To manage the storage and placement of data sets, DFP uses a catalog and a volume table of contents (VTOC). The catalog contains information about the data set and identifies the volume on which the data set resides. The VTOC lists the data sets that reside on specific volume, as well as information about the location and size of each data set.

Users submit requests for processing large volumes of data that relay on the computer's speed. In early days, requirements contain both scientific and business applications. Both data and source programs were contained on punch cards. Subsequently, jobs and programs were submitted to the computer in a giant batch, which placed little demand on the user. The ability to store data and programs on magnetic tape and subsequently on disks, and other DASDs, allowed more data to be stored. So, for example, instead of storing its order entry, for inventory, a company might store the status of each customer's order. In this way, large databases began to develop. The users were able to use applications to browse and summarize the data. The result was the development of transaction-oriented systems such as CICS and a hierarchical database called IMS (Information Management System) that could query the databases and make the data available for a large user community on a real-time basis.

Transaction-oriented systems provided high performance for a large number of users on a timely basis, which meant an increase in revenue rather than simply a way to cut costs. And business that took advantage of computers gained a very decisive competitive edge. As computer processing became faster and less expensive, it was practical to use terminals to connect many users directly to the computer, thus on-line applications began to proliferate. At this point, the terminal became the primary I/O device and the user's means to interact with the CPU. In fact, to many users the terminal was synonymous with the computer.

Interactive access to MVS is made possible by TSO/E (Time-Sharing Option/Extension). TSO/E allows a wide variety of users to perform many different kinds of tasks. For example, a systems programmer can use TSO/E to keep MVS and associated products running smoothly. A business professional can use TSO/E to access data from a corporate database, and an application programmer can use the software to edit, compile, and test application programs. TSO/E can handle short-running applications that a use a few resources, as well as long-running applications that require large amount of resources.

Crucial MVS functions are backed up by recovery routines that run only when an error occurs. A recovery routine isolates an error and tries to confine it a single user or task. At the same time, the recovery routine collects information about the error so that if a system failure does occur, the reasons for the failure can be quickly determined and isolated. In addition, MVS enables the computer system to remain available despite hardware failures. For example, if a device fails, MVS isolates the piece of hardware and continues to run with the remaining devices. In a multiprocessing environment, MVS can recover form failure of a processor and continue to work on the remaining processors.


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