Mainframe: Top IMS DC Interview Questions (2 of 2)

1) Which block MFS uses for input message?

DIF- Device input format

2) What is second block it uses?

MID- Message input descriptor

3) Which block application program uses for output messages?

MOD-Message output descriptor

4) What is next block it uses?

DOF- Device output format

5) What are 3 groups of MFS control statements?

  • Device Format Control Statements
  • Message descriptor control statements
  • Compilation Control Statements

6) What are FMT and FMTEND?

FMT: Identifies the beginning of a device format
FMTEND: Control statements end with a FMTEND statement

7) What is MDT tag in IMS DC?

  • MDT tag indicates whether or not the data in the field has been changed by the terminal user since the screen was sent to the device.
  • When a screen is displayed, MDT’s of fields is OFF.
  • Advantage: Telecommunications Efficiency

8) What are JUST and FILL?

JUST parameter specifies how data should be positioned in a message field. Default is Left Justification
FILL parameter specifies what pad character MFS should use to complete a field when the data that’s mapped into it doesn’t fill. you with
Ex: FILL=C’0’

9) How to get multiple physical pages?

MFS provides a facility to generate a single physical input message from multiple physical pages.

10) How to send message to multiple destinations?

The application Program that’s processing a Single Input Message can send multiple Output Message to Multiple Destinations.
–ISRT call is issued but only difference is that the call specifies Alternate PCB instead of I/O PCB.

11) How terminal works with data?

There are three ways to maintain Data between Terminal Interaction.
•Store Data in the Terminal Screen.
•Store Data in the Databases
•Store Data in the IMS provided Scratch Pad Area.

12) What is SPA?

A conversational Program must use a SPA(Scratch pad area)
–A Unique SPA is associated with each terminal that’s running a conversational transaction.

13) How recovery happens in IMS DC?

If an Application Program Abends, IMS automatically reverse or Rollback the changes it has made to the Databases and Message Queues.

14) How CHECKPOINT works in IMS DC program?

The checkpoints are taken automatically with each transaction a program processes. (This is called Single Mode Processing.)
–In Multiple Mode Processing, the only automatic checkpoint is at the End of the Program. However, the program can force a checkpoint by issuing CHKP call, which causes IMS to write a Checkpoint Record to the Log.
–The Checkpoint Call Syntax:


Author: Srini

Experienced software developer. Skills in Development, Coding, Testing and Debugging. Good Data analytic skills (Data Warehousing and BI). Also skills in Mainframe.