The mainframe is used by businesses these days as they are very high-performance computers. Mainframe computers can process huge amounts of calculations and transactions in real-time. They have a large amount of memory and processors for processing a huge amount of data for big business houses. While appearing for an interview to advance the mainframe in an organization, you would need to be well equipped with different types of small details about the mainframe which the interviewer may ask you about. The questions might get very in-depth and technical, and for that, thorough knowledge is required. Here we have listed the top 50 mainframe interview questions and answers that an interview board may ask to evaluate your knowledge levels.    

List of Interview Questions

Following are the top 50 mainframe interview questions :

  1. What is meant by mainframe testing?

Mainframe testing refers to the testing of computer code services and applications. It is sometimes performed on deployed code victimization into the input data.

2What role does mainframe testing plays?

Testing plays an important role in application development, improving the quality of the systems and also the price point.

3. Name the various attributes of mainframe computing?

There are 5 attributes of mainframe computing, and they are virtual storage, multiprogramming, batch processing, time-sharing and spooling.

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

Dynamic SQL is SQL statement that is constructed at runtime, and so these statements cannot be hard-coded into the application. This statement is ready throughout the execution of the associate degree SQL application. At the same time, static SQL is a SQL statement that does not change at runtime and can be hard-coded into the application.

5. What do you mean by spool?

The full form of the spool is Simultaneous Peripheral Operations On-Line. It is a buffering mechanism in which data is temporarily held to be used and executed. Spooling works in a way that accumulates data, processes and instructions from multiple sources for execution later on.

6. What is the function of an update cursor?

Rows of data can be updated as you retrieve them by using a cursor. The information server places an additional lock on rows fetched once it is fetched, a less exacting lock is placed.

7. Name the different types of Table spaces?

 There are 3 types of spaces; they are simple, segmented and partitioned.

8. Name the divisions in a COBOL project?

A COBOL program has 4 divisions, namely the identification division, the environment division, data division and the procedure division.

9. Explain the difference between index and subscription?

Index refers to the number of displacement positions in an array, and it does not need to be declared in the working storage section. An index is much faster and is initialized by using the SET operator and is also incremented by the set up by the operator. 

Subscription refers to a number of occurrences in an array that will be declared in the working storage section. Subscriptions are slow in access and initialized using MOVE statement and incremented using ADD operator.

10. What is table declaration in COBOL?

Arrays in COBOL are known as tables, and this is a linear data structure and a collection of individual data items of the same type. Occurs clause is used to define a table that can be used only with level numbers starting from 02 to 49.

11. What is lock contention?

Lock contention is when more than one object seeks to get executed simultaneously as DBD allows entry to one object at a particular time. It occurs when one process or thread attempts to acquire a lock held by another. 

12. Name the types of locks?

There are 3 types of locks, and they are shared lock, update lock and exclusive lock.

13. Explain the functioning of the 3 types of locks?

Shared lock – This type of lock allows 2 or more programs to read from the locked space at a time, but they are not allowed to change it.

Update lock – This type of lock permits the program that uses its space to change it.

Exclusive lock – This lock type restricts all type of users from accessing the locked space.

14. What do you mean by COMP-1 and COMP-2?

COMP-1 refers to a short or single-precision floating-point format, and it occupies storage of 4 bytes.

COMP-2 refers to Long or double-precision floating-point format, and it occupies storage of 2 bytes.

15. What is the difference between SEARCH and SEARCH ALL?

SEARCH is a serial search that is used for single-dimensional and multi-dimensional arrays.   

SEARCH ALL is a binary search and is used only for a single dimensional array. The table must be sorted before using this.

16. What is meant by binary search?

Binary search or logarithmic search is a search algorithm that finds the position of a target value by comparing it to the middle element of the array within a sorted array.

17. How can a binary search be used?

Binary search is faster than a linear search, but the array needs to be sorted before applying a binary search. Binary search can be used to solve a wider range of problems like finding the next smallest or the largest element in the array.

18. How is a sign stored in a comp-3 field?

Comp-3 stores a sign in a low order, half a byte of the field or the last nibble. 

19. What is a confinement level?

It is that level which the initiation assembles in the centre if it is disconnected from the actuation bunches.

20. What is Alias?

This is described as a situation in which a data location in memory can be accessed through different names in the program, which means that modifying the data in one of the names will modify all the data.

21. What is NOTCAT2?

NOTCAT2 in the database demonstrates the nearness of a copy inventory.

22. What is SPUFI?

SPUFI is a menu-driven abridged type of SQL processing.

23. What is INSPECT?

It is COBOL verb and is used to discover the number of times a certain string shows up.

24. What is the full form of DRDA?

DRDA is the acronym for Distributed Relational Database Architecture.

25. How to create a LIKE table?

I can be created by using LIKE parameter in the statement CREATE.

26. Where is the VSAM KSDS placed?

It is placed at the BSDS.

27. What are the file-OPEN modes?

There are 4 file-OPEN modes, and they are input, output, extend and I-O.

28. What is meant by the linkage section?

Linkage maps to the specific data in the program’s working storage.

29. Can min or max be used with alphanumeric data?

Yes, it can be used.

30. What is a linkage segment?

It is a part of a program that maps information things in the working stockpile of the program.

31. What are foreign keys?

These are properties of a particular table having matching entries in some other table to a primary key.

32. How is JCL used for testing batch programs?

In a batch atmosphere, a JCL is used for running programs.

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

Composite index consists of combined values of 2 columns of a table, whereas multiple indexes are 2 indexes for each column of the same table.

34. What is the status of 88?

It is conditional names.

35. What is ISER NUMERIC Rule?

The NUMERIC TRUE to the item only 0-9, but if the tested item is a signed item, then it can have 0-9, and -.

36. What is A COPYBOOK in COBOL?

It stores the format for any record and uses the format design for other programs.

37. What is the difference between INCLUDE and COPY?

INCLUDE is used for expanding the design at a pre-compiler time, and COPY is used to expand the design at a compiler time.

38. What is a self-referencing constraint?

It restricts the changes that can be made to the primary key through a foreign key.

39. What is the difference between Type 1 and Type 2 indexes?

In the Type-1 index, the data pages are locked, but in the Type-2 index, the index pages are not locked.

40. What is the difference between HIDAM and HDAM databases?

HIDAM has a separate index file, while HDAM does not have a separate index file.

41. What is meant by referential integrity?

This states that consistency needs to be maintained between primary keys and foreign keys.

42. What is STOPRUN?

It stops the current execution of work from returning control to the operating system.

43. How is EXIT PROGRAM used?

It is used to quit one program and allow another program to pursue.

44. What is Database Descriptor?

It provides restricted access to the database when objects get altered or created.

45. What is IMS?

It is a database and transaction management system for mainframe systems.

46. What is the full form of CICS?

CICS is the acronym for Customer Information Control System. 

47. What is EIB?

EIB is a control block that is loaded automatically by the CICS for every program.

48. What are the categories of mainframe manual testing?

It can be classified into 2 categories, and they are batch job testing and online testing.

49. How are Start and Xctl different from each other?

Start is for the beginning of new transactions, whereas Xctl takes the operations further.

50. How the Type-2 index is superior?

In this type of index, even if the data pages get locked, the index pages are still accessible. 


Working in the advancement of mainframe might be a great job if you are looking for being a part of the huge data processes and calculations of business houses. These mainframe interview questions will help keep in your mind when preparing for this kind of interview. Keep yourself interview ready with these top 50 mainframe interview questions and answers.

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