52 Mainframe Interview Questions With Sample Answers

By Indeed Editorial Team

Updated 2 September 2022

Published 3 January 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

A mainframe is a central data hub that ensures a centralised form of computing. Maintaining computer applications with mainframe systems is essential to keep the system operational and online. If you are a mainframe developer looking for your first job or career advancement, it may be beneficial to prepare answers to commonly asked mainframe interview questions. In this article, we cover 52 most-asked questions in a mainframe interview and provide seven example answers.

General Mainframe Interview Questions

Below are 15 general mainframe interview questions that can help an employer understand your skills and experience with mainframe:

  1. Tell me about your experience with the mainframe.

  2. How does your experience support this job role?

  3. What task do you least enjoy when working with mainframes?

  4. How do you prioritise your time when working on multiple mainframe projects simultaneously?

  5. How has knowledge of the mainframe influenced your career growth?

  6. How do you explain a technical problem to a colleague unfamiliar with mainframe computing?

  7. How do you keep yourself updated with the latest development in mainframe computing?

  8. How has your educational qualification prepared you for a programming job?

  9. What certifications do you have that supports your expertise in the mainframe?

  10. How did you resolve problems in your previous job? Explain the project and process you went through to resolve the issue.

  11. Tell me about a time when you showed initiative as a mainframe developer.

  12. Describe your accomplishments as a mainframe developer.

  13. How do you keep yourself motivated during complicated projects?

  14. According to your knowledge, what is the future of mainframe computing?

  15. Describe how you complete a project from start to finish.

Related: How To Answer 9 Common Interview Questions For Freshers

In-Depth Interview Questions

An employer wants to understand your technical skills and expertise in mainframe computing by asking in-depth and technical interview questions. Here are some commonly asked interview questions:

  1. Explain the importance of DBCTL.

  2. Elaborate on the types of conditional statements in COBOL.

  3. How do you ensure a program executes above 16 Meg Line?

  4. How do you resolve deadlock or -911 errors in the DB2 program?

  5. Explain the difference between STATIC and DYNAMIC CALL proclamation.

  6. What is CICS and what are the CICS transactions?

  7. Explain the purpose of Execute Interface Block (EIB).

  8. How do you declare host variables?

  9. How are TYPE1 and Type2 indexes different?

  10. Outline the difference between HDAM and HIDAM.

  11. How are external and global variables different from each other?

  12. What are various forms of Evaluate statements?

  13. What are the benefits of mainframe computing?

  14. What is the difference between static and dynamic SQL?

  15. How do you use JCL for testing batch programs?

  16. How is delimited by size and delimited by space different from each other?

  17. Can you move the values of alphanumeric to a variable numeric?

  18. Explain confinement level.

  19. Explain the importance of the secondary index in IMS.

  20. What is the difference between multiple and composite indexes?

  21. What is the importance and effect of using foreign keys in a table?

  22. How do developers avoid deadlocks while reading data in the mainframe?

  23. How do you verify if a file is empty in JCL?

  24. Elaborate on the difference between NEXT SENTENCE and CONTINUE UNIQUE.

  25. What do you mean by referential integrity?

  26. Explain database descriptor.

  27. When do you use the JOB statement?

  28. What are host variables and how do you declare them?

  29. How can you resolve the SOC-7 error?

  30. Is it essential to use DCLGEN?

Related: Technical Interview Questions And Example Answers

Mainframe Interview Questions With Answers

Reviewing questions with sample responses can provide you with some additional perspective on answering questions during an interview. Below are a few questions with answers to help you understand how to answer questions such that it impresses an interviewer:

1. What is MDT?

When working with mainframes, knowing different attributes is essential. When answering such questions, be concise while demonstrating your knowledge and understanding of the concept. Be sure to list the purpose and importance of using MDT.

Example: “MDT or Modified Data Tag is a one-bit of attribute character. Mainframe developers use it because MDT allows screen modification of the field. When a user changes the MDT field, MDT turns on automatically. A value of 0 shows that MDT is off and no modifications are in process. But if the value is 1, it shows MDT is off and the terminal operator changes in the field. Also, MDT helps improve performance and reduce or control the data traffic in the communication lines.”

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2. What is the functions of three types of locks?

An interview may ask a technical question to establish your understanding of the mainframe. As locks prevent an application from accessing uncommitted data, they are helpful in mainframe development. Explain all three lock types to show your technical knowledge when answering this question.

Example: “The three types of locks are shared (S lock), update (U lock) and exclusive (X lock). In the shared lock, multiple users can read and access the information but cannot change the locked space. As users cannot make changes, the shared lock avoids concurrent changes. The update lock is a permissive lock that allows a program to read and change the locked space.

While the X lock gives exclusive access to the database object, no transaction can take place until the X lock is in effect. The exclusive lock allows a read after completing the update request and provides full protection to the data in the locked space.”

3. What is the difference between INCLUDE and COPY?

When working with the mainframe, developers often come across multiple terms having the same meaning and functions but are not the same. It is common for interviewers to differentiate between similar terms and their functions.

Example: “While INCLUDE and COPY help in expanding the layout defined in the copybook, there is a slight difference in its usage. INCLUDE executes at the pre-compilation stage by the SQL compiler, whereas COPY executes at the COBOL compiler's compilation stage. Also, INCLUDE can expand all DB2 members, while COPY can expand only COBOL file layouts. You cannot use COPY to expand DB2 members, but you can use INCLUDE to expand COBOL file layouts.”

4. What is DRDA?

An interviewer can ask important questions about the technical aspects of the mainframe. When answering a technical concept, provide the definition and focus on elaborating on the benefits of using DRDA in mainframe computing.

Example: “DRDA or Distributed Relational Database Architecture is a connection protocol that programmers use for local database processing. DRDA provides an open and robust distributed database environment. It primarily defines rules for accessing distributed data. It allows applications to access multiple tables at different locations. DRDA also consists of a different set of rules used for communication between a DBMS and application.”

5. Differentiate between multiple and composite indexes?

When working in mainframe computing, you may encounter multiple terms with the same meaning. These functions and terminologies are not the same. When answering such questions, clearly differentiate between similar terms and their functions.

Example: “Composite and multiple indexes may seem similar, but there is a key distinction between the two. Multiple indexes use two indexes for two different columns of a table. In contrast, a composite index uses only one index of combined values from two columns in a table.**"

6. When creating a table, you give the size of one field as 12, but the client specifies the requirement as 10. How can you solve this problem?

This question tests your core knowledge in mainframe computing. Be concise and use simple language to explain the steps you follow to solve the problem. Give an accurate answer that shows your technical knowledge of mainframe computing.

Example: “In mainframe computing, if a table is empty, I can alter the column to any length, but if there is some data present in the table, I can only reduce the column length to the largest data size available in that particular column.”

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7. What is JCL in the mainframe and explain the different JCL statements for a job?

Employers may ask this technical question to gauge your mainframe proficiency. Explain the concept and provide details about the various JCL statements for a job.

Example: “JCL is a job control language, a scripting language used to instruct the system for a batch job. Using the JCL language, developers create code that tells the operating system what action to perform. There are three main types of JCL statements for a job. The first statement identifies the work that an operating system performs, while the second statement, which is the EXEC statement, identifies the number of job steps within the job. The third statement or DD statement identifies the output and input datasets.”

Please note that none of the companies, institutions or organisations mentioned in this article are associated with Indeed.


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