Mainframe Interview Questions


Answering questions in front of your entire class was too difficult for you in your school or college days because you were not prepared at the time when the teacher or lecturer used to ask questions to you. Similarly, in an interview, you never know what an interviewer may ask you to judge your skills and expertise. However, with the help of our Mainframe interview questions and answers, it has just become easier for you to determine what are the questions usually asked in the interview and how to answer them appropriately so that you get the job that you are waiting for.

About Mainframe

The mainframe is basically computers that are used primarily by large companies and organizations to perform critical tasks in complex applications. They use mainframe computers to process bulk data like census, consumer statistics, industry and market statistics, planning of enterprise resources, transactions processing, and lots more processes that deal with a huge amount of data. They are quite larger in size and have more amount of processing capabilities than servers, minicomputers, or any other workstations. These system architectures were introduced in the early 1960s but continued to develop for years together. These mainframe computers are often utilized as servers in these huge companies and organizations.

Best Mainframe Interview Questions of 2022

1. What is DRDA?

DRDA stands for Distributed Relational Database Architecture. It works as a connection protocol for local database processing. Database vendors like IBM use it. This architecture contains a set of rules that helps communicate between any application and database relation.

2. What is the function of the clause were in mainframe programming?

While working with a relational database system, the clause “WHERE” isolates an element or a row.

3. Explain how the LIKE table can be created?

You can use the LIKE parameter and the CREATE statement to create the LIKE table. These tables are needed during the testing phase of the production environment.

4. How is runstats used in environment testing?

The catalog columns are filled with default values and the end result during environment testing may not produce accurate results. Runstats is used to clear the default values of these columns.

5. What is the need of a secondary index in IMS?

It is a substitute path into any IMS database. It can be used as a file to acquire required data.

6. Explain foreign keys?

Foreign keys are properties of a particular table having matching entries to a primary key in some another table. This results in the formation of a relation between the two tables.

7. Write about the self-referencing constraint?

It limits the changes that can be made to the primary key from a foreign key. For this purpose, the foreign key has to define a DELETE CASCADE rule.

8. What does a deadlock mean in DB2?

When two independent processes contend for the same resource or the resources reserved by one another, it is called a deadlock. -911 and -913 are the SQLcode for a deadlock.

9. What is the function of DBCTL?

It is used to access IMS files for CICS Transactions and it is an address space. PSBs, DBDs, IMS files and ACBs are fixed into DBCTL for file access. Now if an IMS call is generated by a CICS program the processing gets transferred to DBCTL to be carried, and the result is sent as reply.

10. How are TYPE 1 and TYPE 2 indexes different?

TYPE 2 index is available for DB2V4. In this type, the data pages get locked, but the index pages are not locked. Therefore, TYPE 2 index are faster.

11. What are the different types of Table spaces?

There are three table spaces, namely:

  • Simple
  • Segmented
  • Partitioned

12. Write the difference between HIDAM and HDAM databases?

HIDAM has a separate index file which is based on the root segment. This file has information regarding the pointer that marks the position of the data. On the other hand, HDAM file does not have separate index file, but the key field of every record is passed through a randomizer which places the record to a particular position in the database.

13. Explain referential integrity?

It is the rule that states that consistency needs to be conserved between the foreign and primary keys. This means that each foreign key entry needs to have a fitting primary key entry.

14. How are composite and multiple indexes different?

Multiple index are two indexes, one each for a column of the same table. Composite index is only one index, which consists of combined values of 2 columns of a table.

15. What is the advantage in De-normalizing tables in DB2?

It lowers the requirement for executing intensive relational joins. It also cuts the number of required foreign keys.

16. Explain Database Descriptor in brief?

DBD, short for Database Descriptor, restricts access to the database when objects get altered, created or dropped.

17. State the maximum value up to which volumes can be inserted to an STOGROUP?

Volumes can be inserted up to 133. Practically though, only 3-4 volumes, when added to an STOGROUP, becomes hard to manage and monitor.

18. Explain delete-connected tables?

Tables, which are related through a foreign key, are known as delete-connected tables. This is because whenever any entry in the primary key is deleted, it affects the values in the foreign key table too.

19. Explain lock contention?

The DBD only allows entry to one object at a particular time. Lock contention is said to happen when more than one object seeks permission for execution simultaneously.

20. What is SPUFI?

SPUFI is the abbreviated form of SQL Processing Using File Input. It is a menu-driven tool which the developers use to make objects in the database.

21. What is an alias?

It is a substitute to a synonym. Aliases are developed for distributed environments so as to avoid the use of location qualifier of a view or table. It is not dropped when the table gets deleted.

22. What is the place for VSAM KSDS?

It is the BSDS.

23. Name and explain the type of locks?

There are three types of lock, namely:

  • Shared – This type of lock permits two or more programs to read from the locked space but does not allow them to change it.
  • Update – This lock is more lenient. It permits the program to read and change the locked space.
  • Exclusive – This lock restricts all users from accessing the locked space.

24. What do you mean by the custom field in Mainframe?

Custom fields are also known as post meta. Post meta is a feature in Mainframe which allows post authors to add additional information at the time writing a post. Mainframe stores this information as metadata in key-value pairs. Users can later display this metadata by using template tags in their Mainframe themes if required.

25. Explain isolation level?

Isolation level is the degree to which the activation group in focus is isolated from the activation groups executing at the same time.

26. What is NOTCAT2?

It is an MVS message that indicates the presence of a duplicate catalogue in the database. This problem can be fixed by removing one of the entries and then adding a new one.

27. What will happen if both STEPLIB and JOBLIB are specified?

JOBLIB is a Data Definition statement. It determines the location of the program, which called the EXEC statement. JOBLIB applies to all steps present in that whole job. It is not possible to use it for catalogued procedures. STEPLIB is very similar JOBLIB. It determines the dataset in which the program exists. It applies only to one step and not the entire job. STEPLIB can be used at any position in the job step and can also be used for catalogued procedures.

In a situation when both STEPLIB and JOBLIB are specified, JOBLIB will be ignored by the system.

28. State the difference between JES2 and JES3?

In JES3, the allocation of data sets for the steps takes place even before the job is scheduled for execution. While in JES2, this allocation takes place just before the execution of each step.

29. State all the File OPEN modes?

The four File Open methods are:

  • I-O
Career scopes and salary scale

With the growth in the computer industry sector over a period of time, mainframe computers are considered as the backbone for most of the companies who rely on servers. Although, all the companies rely on servers to carry out their daily tasks, however, it depends on the usage of the mainframe computers. Therefore, there are many companies who are hiring developers and system architects who are well-versed in handling these mainframe computers. Hence, the scope and opportunities for you getting a job are high. As a fresher, you can earn up to 78,000 dollars to 80,000 dollars per annum, and if you are experienced, then you can up to 163,000 dollars per annum.


There are a lot of scopes and opportunities for you to work in this specific sector if you want to pursue a career. However, cracking the interviews is the most difficult task, which can be dealt with if you follow our Mainframe interview questions and answers.