In earlier days, the Mainframe systems were computers basically used by the large organizations for processing large amounts of data. These are high performance systems possessing processors and memory components of various combinations. In the 21st century still there is a need for Mainframe Developers in many companies across the globe. While attending a Mainframe Interview, it is important to know the below given important Mainframe Interview questions and answers. 

Most Important Mainframe Interview Questions and Answers

1. What are the advantages of Mainframe Computers?

    1. Powerful performance capabilities
    2. Highly reliable
    3. Highly scalable

2. Where is the Mainframe technology used?

Mainframes are used in various real time applications such as business transactions, accounting, etc…..       

3. Expand DRDA.

Distributed Relational Database Architecture.      

4. What are the disadvantages of Mainframe technology?

  1. They require a special Operating System (OS)
  2. They are expensive
  3. Occupies more physical space

5. What is SPOOL?

SPOOL stands for Simultaneous Peripheral Operations Online. It is a mechanism in which the data is usually stored on a larger storage medium, so that it can be retrieved at some other time. 

6. What is the difference between supercomputers and mainframes?

Supercomputers are used for solving large complex mathematical operations, while the Mainframes are used for processing bulk amounts of data.

7. Expand SPUFI.

SPUFI stands for SQL Processing Using File Input.

8. Expand QMF. 

QMF stands for Query Management Facility.

9. How is QMF different from SPUFI?

With SPUFI, one can execute multiple queries at a time, whereas in QMF one       cannot execute multiple queries at a time.

10. Expand JCL.

JCL stands for Job Control Language. 

11. List out a few conditional statements present in COBOL language.

  1. IF condition
  2. Relation condition
  3. Negated condition
  4. Combined condition

12. Mention different types of table spaces.

Simple, Segmented and Partitioned 

13. Mention a few differences between Index and Subscript.



1. INDEXED BY phrase is used for declaration.  

  1. There is a need for a separate declaration with S9(04) COMP in WORKING STORAGE SECTION.

2. It is faster in accessing table data items.

    2. It is slower in accessing table data                         items.    

3. SET statement is used to initialize the INDEX

    3. MOVE statement is used to initialize    the Subscript.  

14. Why is Index faster than Subscript?

Because Index represent an offset into the array rather than being converting the occurrence number into the offset.

15. How do you create an Index?

We can create an Index by using the INDEXED BY phrase of the OCCURS clause to identify an index name.

16. What is the range of Subscript values?

Subscript values range from 1 to the number of times the table occurs. It can be any non-negative number.

17. What is the keyword/clause used to define a table in COBOL

An OCCURS clause is used to define a table/array in COBOL.

18. What are the two different types of tables?

Tables are classified into two types. They are:

  1. Fixed-length tables and 
  2. Variable-length tables

19. Define Fixed-length tables.

It specifies the number of OCCURS statically. The tables are defined with the number of OCCURS specified with a static value while writing the program.        

20. Define Variable-length tables.

It specifies the number of OCCURS dynamically. The number of occurrences value specified while running the program.

21. What are level numbers?

A level number is a one or two-digit value that describes the level of the hierarchy of data entries or items.   

22. How many types of locks are there in db2?


23. What is deadlock in db2?

A deadlock is a special situation where multiple processes try to access the same resource simultaneously and wait for the other process to release the resource.

24. What is a ‘view’ in db2?

A view is another method of representing the data present in one or more parent tables. A view of a table may contain a few columns and rows of the major table.

25. What is a Cursor?

A cursor is used to retrieve information and a process the returned data one by one.

26. List out some of the symbols used in a Picture Clause.

  1. 9 - Numeric Character
  2. A - Alphabetic Character
  3. X - Alphanumeric Character

27. What is the syntax to create a storage group in db2?

db2 create stogroup on ‘path’

28. What are joins in d2?

Joins are used to combine multiple tables into a single table. 

29. What is the use of an aggregate function?

An aggregate function is used to perform mathematical calculations on a set of values and returns a single numerical value. 

30. What is the difference between UNION and JOIN?

After applying UNION, the data appears in rows, whereas for JOIN, the data appears in columns.

31. How many ways can the parameters be passed between programs?

Two ways.

32. Is COBOL a structured language?


33. How many divisions are there in a COBOL program?


34. What is the difference between Call by Value and Call by Reference?

In case of Call by Value, the actual value is passed on from one program to  another, whereas in case of Call by Reference, the address of the value is passed on to another program.

35. How many types of statements are there in JCL?

There are three types of statements in JCL. They are:

  1. JOB
  2. EXEC and 
  3. DD

36. Expand JES.

JES stands for Job Entry Subsystem.

37. Is JES3 centralized?


38. Expand GDG.

GDG stands for Generation Data Group.

39. What does S03D represent?

It is used when an error occurs in opening an indexed sequential or direct access dataset.

40. List out a few types of VSAM datasets.

  1. Entry Sequenced Data Set 
  2. Linear Data Set 
  3. Key Sequenced Data Set 
  4. Relative Record Data Set 


1. Why do you choose Mainframe?

There are several reasons why one can choose Mainframeis its high performance, powerful processing capabilities and it is reliable. 

2. What is JCL in Mainframe?

JCL stands for Job Control Language. It is a set of statements that tell the mainframe OS to perform the work that you want.

3. Expand DB2?

DB2 is a Relational DataBase Management System.

4. Is the Mainframe frontend or backend?

It is related to the backend.

5. Does Mainframe have coding?

Yes, Mainframes have coding.


We hope that this article helps you in preparing for Mainframe technology interviews. These questions and answers will give you the required confidence to crack any interview. If you are looking to upskill further in the software development domain, then we would recommend Simplilearn’s Post Graduate Program in Full Stack Web Development. This course is designed and created in collaboration with Caltech CTME and can help you gain the required skills and knowledge to establish yourself as a highly skilled full stack developer.

If you have any questions or doubts, feel free to post them in the comments below, and our team will get back to you at the earliest.

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