40+ Important Mainframe Interview Questions and Answers

Most Important Mainframe Interview Questions and Answers

1. What are the advantages of Mainframe Computers?

Mainframes are known for their high performance, reliability, and scalability. They are capable of handling millions of transactions per second, making them essential for enterprises.

2. Where is the Mainframe technology used?

Mainframes are widely used in industries like banking, insurance, retail, and government. They support critical applications such as real-time transaction processing, accounting, and payroll.     

3. Expand DRDA.

DRDA stands for Distributed Relational Database Architecture. It allows applications to access distributed databases as if they were a single system.

4. What are the disadvantages of Mainframe technology?

• They require a special Operating System (OS)
• They are expensive
• Occupies more physical space

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5. What is SPOOL?

SPOOL (Simultaneous Peripheral Operations Online) is a technique where data is stored temporarily on disk before being sent to a device such as a printer. This improves efficiency by allowing jobs to be queued and processed sequentially.

6. What is the difference between supercomputers and mainframes?

Supercomputers are designed to perform complex mathematical and scientific calculations at very high speeds. Mainframes, on the other hand, are optimized for large-scale data processing and transaction management.

7. Expand SPUFI.

SPUFI stands for SQL Processing Using File Input. It is a DB2 tool that allows users to execute SQL queries stored in a file and view the results.

8. Expand QMF. 

QMF stands for Query Management Facility. It provides an interactive environment for executing SQL queries and generating reports.

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. It is used to instruct the mainframe operating system on how to run a job, what resources to use, and how to handle input and output.

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

• IF condition
• Relation condition
• Negated condition
• Combined condition

12. Mention different types of table spaces.

In DB2, table spaces can be Simple, Segmented, or Partitioned. Each type determines how data is stored and managed within the database.

13. Mention a few differences between Index and Subscript.

14. Why is Index faster than Subscript?

An Index directly stores the memory offset of an element within an array, allowing the system to access data immediately. A Subscript, on the other hand, represents the occurrence number in the array and must be converted into an offset at runtime, which slows down processing.

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:

• Fixed-length tables and 
• 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.        

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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?

DB2 supports three types of locks: shared, exclusive, and update locks. These control access to database objects and prevent conflicts in multi-user environments.

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.

• 9 - Numeric Character
• A - Alphabetic Character
• 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 combine rows from two or more tables into a single result set, based on a related column. Common joins include INNER JOIN, LEFT JOIN, and FULL JOIN.

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?

Parameters can be passed using Call by Value, which sends a copy of the data, or Call by Reference, which passes the memory address for direct modification.

32. Is COBOL a structured language?

Yes. COBOL supports structured programming constructs like loops and conditionals, making programs easier to read, debug, and maintain.

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

There are four divisions: Identification, Environment, Data, and Procedure. Each division serves a specific purpose in structuring the 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?

36. Expand JES.

JES (Job Entry Subsystem) is responsible for managing the input and output of jobs in the mainframe environment.

37. Is JES3 centralized?

No. JES3 is not fully centralized; it provides job scheduling and resource management across multiple processors.

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. The main types of VSAM datasets are:

• KSDS (Key Sequenced Data Set)
• ESDS (Entry Sequenced Data Set)
• RRDS (Relative Record Data Set)
• LDS (Linear Data Set)

FAQs

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.

Conclusion

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 Full Stack Developer Courses. These courses can help you gain the required skills and knowledge to establish yourself as a highly skilled full stack developer.