TOP 56+ Mainframe Interview Questions and Answers

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Avatar for Richard-M-Adrian
2 years ago

In this guide, we will uncover the most asked mainframe interview questions.  

The questions are meant to evaluate one’s skills and knowledge of mainframe computers. 

Read through the top 56 interview questions for Mainframe developers. 

Shall we jump right in? 

1.Explain three main types of locks. 

Exclusive lock - A lock that restricts all programs from accessing any locked space in a computer. 

Update lock - A lock that does not restrict a program from reading or changing information in a locked space. 

Shared lock - A lock that allows multiple programs to access, read and change data in a locked space. 

2.Define referential integrity

  • Referential integrity is a computing principal stating users have to maintain consistently between foreign and primary keys. 

3.Distinguish between composite index and multiple index

  • Composite index consists of joint (or shared values) with two columns on a single table. While multiple indexes are 2 indexes , each for a particular table column. 

4. Explain the difference between Type 1 and Type 2 Indexes

  • Type 1 indexes have locked index pages and the pages load quickly. Type 2 indexes are locked. 

5.Highlight the different types of Table spaces

  • Partitions, segmented and simple Table spaces. 

6. Distinguish between HIDAM and HDAM databases

  • HIDAM sets aside a separate index file on the basis of a root segment. This file stores data about the index’s pointer and denotes where the piece of information is located. HDAM lacks a seperate field. Users access each field of HDAM’s record using a random position in the database. 

7.Differentiate between STOPRUN, EXIT PROGRAM and  GOBACK in COBOL

  • EXIT PROGRAM quits from one program and allows the initiation of another program. 

  • STOPRUN stops an already running program and returns execution back to the OS. 

  • GOBACK gives back control to the executing/calling program.

8.Provide the advantage of De-normalizing DB 2 tables

  • Denormalizing a DB 2 tales reduces the need of executing multiple relational joins. Besides, it eliminates the need for foreign keys. 

18. Define Database Descriptor

Database descriptors give users restricted database access once an object is either dropped, altered or created. 

19. What is delete-connected tables

The act of deleting a primary key - which subsequently affects the corresponding table’s key.

20. Explain DRDA

Distributed Relational Database Architecture or DRDA is a connection protocol for processing local databases. The framework runs through a set of rules that govern communication between the database and applications. 

21. Explain the role of the clause WHERE  in mainframe computing. 

Clause WHERE isolates an element (row) while working with a relational database system. 

22. How do you create the LIKE table?

Using the CREATE statement and LIKE parameter. 

23. How do you use runstats in environment testing? 

Fill catalogue columns with default values.  Since these default values might not give accurate results, Runstats clears all these values. 

24. What is the role of  COBOL’s Linkage Area?

Linkage area facilitates communication between a program written in COBOL with a JCL program using the PARM parameter. 

 25. Explain the function of COPYBOOK in COBOL

COPYBOOK offers storage for record formats and deploys a common design of the record to other programs. 

26. Define the self-referencing constraint

A function that restricts changes across primary keys to foreign keys. For which reason, the program demands the foreign key to initiate a DELETE CASCADE rule. 

27. Explain deadlock in DB2

If multiple programs or computing processes contend for a common resource, and the process hangs, the event is called a deadlock. 

28. Explain the role of DBCTL

DBCTL is an address space that allows users to access files in the IMS. 

29. What is the maximum value for inserting  volumes into a STOGROUP?

Up to 133. However, more than 4 volumes within a STOGROUP become challenging to manage. 

30. Define lock contention

Given that a DBD will only allow an entry to access one object for each given time; multiple objects might seek permission to execute simultaneously and therefore create lock contention.

31. What is SPUFI? 

SQL Processing Using File Input or SPUFI is a menu-driven function for creating objects on the database. 

31. Define an alias

Refers to a synonym or substitute. They are usually not dropped when deleting tables. Also note they are created for distributed environments. 

32.Describe NOTCAT2

An MVS message which shows that a database has a duplicate catalogue. Deleting and adding another entry fixes the problem.

33.Define isolation level

Referes to the extent of an activation group being isolated from currently executing groups within a duration of time. 

34. Explain the event that takes place when both JOBLIB and STEPLIB have been specified

JOBLIB helps locate a program that called an EXEC statement. STEPLIB defines the dataset within which a program is contained.  If both functions are called at the same time, the system ignores the JOBLIB.

35. Differenciate  between JES2 and JES3

JES2 takes place immediately before execution of each computation step while JES3 takes place before the system schedules the execution process. 

36. List File OPEN modes




  • I-O

37.What is the difference between CONTINUE and NEXT SENTENCE?

CONTINUE uses the scope terminator to hand over the flow of control. While the NEXT SENTENCE  uses the program period to hand over program flow to another execution statement. 

38. Why should developers create COMMITS as batch programs? 

A COMMIT statement will release the lock for a program unit and initiate the execution of an upcoming program.  Failure to insert COMMITS makest the program to keep going back and forth; which takes extra processing time. 

39. How do you retrieve data from more than one table using the single SQL statement ?

You can retrieve data from multiple tables using  nested selects , joins and unions. 

40.Briefly describe a “view” 

Refers to a virtual table that uses data from other views and base tables. 

41. Define the parameters that mainframes use to control free space in a database

PCTREE -A percentage value of the free space a page will contain

FREEPAGE  - Definesa specific amount of pages that will load just before a space/page is left empty.

42. What maximum value of tables can you join? 

You can join a maximum of upto 15 tables

43. Define Index cardinality 

Index cardinality is the amount of discrete entries within a column. 

44.what is a clustered index? 

Columns within a clustered index are maintained within the same row sequence until the system frees adequate memory. 

45. List four types of lockable units in DB2

Indexes sub page


Table space


46. Define the role of INITIALIZE

Reffers to setting the alphabetic and alphanumeric  fields to ‘’(space). And then setting the parameter fields for numeric to  “0”

47. Explain the importance of COMMON attribute

Allows nested programs or lines of code to utilize functions within a program written in COBOL

48. Can you access ESDS records randomly? 

You can randomly access ESDS records using the Relative Byte Address( or RBA). Note its impossible to delete the records. 

49. Why does the KSDS dataset leave free space?

A system creates free space at regular intervals while allocating KSDS datasets.This space is meant for keeping program data organized and sequentially.

50.What are clusters? 

Refers to a combination of data portions, index and sequence set in a data set.  The operating system gives the cluster access to program execution. Which allows all dataset portions to run simultaneously.

51. Explain the function of CURRENTDATA option during bind

The program can fetch blocks when selecting rows within a table.  The value of the function is NO by default.  This means you should change it to YES. However, this also varies from one DB2 version to another. 

52. How do you achieve record locking in DB2 versions that do not offer support? 

Through customizing the size of the record length to become atleast half of the page. 

53.When should one use an inline program? 

Use an inline program only when the action body does not need to be utilized in other columns.  If this code should be executed within other programs, custom package the code and utilize a PERFOM paragraph. 

54. Talk briefly about Path

This is a file which makes it possible for processes to access files using alternate indexing.  The path defines the relationship between the AIX and the base cluster. 

55. Define what is the role of IEBGENER

Allows developers to copy one SAM file to an external source or resource.  You can perform data reformatting using the IEBGENER by supplying control cards through the SYSIN. 

56. Explain the result of declaring ON SIZE ERROR

The condition is true so the execution on the ON SIZE ERROR runs.  The content however will not change. Failure to mention the phrase, runs the statement with a truncation.


Are you looking to further your career in Mainframe development, evaluate your knowledge with the above questions and get going.  There are numerous opportunities for this skillset and you should get going as soon as possible.

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