Advantages to using MFS
Two primary advantages to using MFS are that it simplifies the development and maintenance of terminal-oriented application systems and improves online performance.
To simplify IMS application development and maintenance, MFS performs many common application program functions and gives application programs a high degree of independence from specific devices or remote programs.
With the device independence offered by MFS, one application program can process data to and from multiple device types while still taking advantage of their different capabilities. Thus, MFS can eliminate or minimize the changes in application programs when new terminal types are added.
MFS makes it possible for an application program to communicate with different types of terminals without having to change the way it reads and builds messages. When the application program receives a message from a terminal, how the message appears in the program's I/O area is independent of the kind of terminal that sent it; the appearance depends on the MFS options specified for that program. If the next message that the application program receives is from a different type of terminal, the user does not need to do anything to the application program. MFS shields the application program from the physical device that is sending the message in the same way that a database program communication block (PCB) shields a program from the data in the database and how it is stored.
Other common functions MFS performs include left or right justification of data, padding, exit routines for validity checking, time and date stamping, page and message numbering, and data sequencing and segmenting. When MFS performs these functions, the application program handles only the actual processing of the message data.
The following figure shows how MFS can make an application program device-independent by formatting input data from the device or remote program for presentation to IMS, and by formatting the application program data for presentation to the output device or remote program.
MFS also improves online performance of a terminal-oriented IMS by using control blocks that are designed for online processing. The MFS control blocks are compiled offline, when IMS is not being executed, from source language definitions. MFS can check their validity and make many decisions offline to reduce online processing. In addition, during online processing, MFS uses look-aside buffering of the MFS control blocks in order to reduce CPU usage and the channel costs of input/output activity.
Because MFS control blocks are reentrant and can be used for multiple applications, online storage requirements are reduced. Optional main-storage indexing and anticipatory fetching of the control blocks can also reduce response time. IMS gains additional performance improvements, because multiple I/O operations can execute concurrently in loading the format blocks from the MFS format library.
In addition, MFS uses z/OS® paging services to reduce page faults by the IMS control region task.
Finally, MFS can reduce use of communication lines. Compressing and transmitting only the required data reduces line load and improves both response time and device performance.