Mainframes Interview questions

Last updated on Jun 12, 2024

The mainframe is a large and multi-user computer system that performs critical applications, bulk data processing, consumer statistics, enterprise resource planning and transactional processing. 

In this article, you can go through the set of Mainframes interview questions most frequently asked in the interview panel. This will help you crack the interview as the topmost industry experts curate these at HKR training.

Let us have a quick review of the Mainframes interview questions.

Most Frequently asked Mainframes Interview questions

Can you name a few software running under the mainframe?

Ans: IBM is the pioneer in the mainframe computing field. Few of mainframe software are COBOL, Enterprise COBOL, JCL, VSAM, CICS, DB2, etc. Other players in the market are Unisys (Clear path), Hitachi (zSeries), HP (NonStop) and Fujitsu(BS2000/ ICL VME) amongst many others.

What is DRDA?

Ans: DRDA is an acronym for Distributed Relational Database Architecture. DRDA is a connection protocol for relational database processing which IBM and vendor databases use. It consists of rules for communication between a remote relational DBMS and the application.

What guidelines should be followed to write a structured COBOL program?

Ans: Following guidelines to be following while writing a COBOL program:

  • Use 'EVALUATE' statement for constructing cases.
  • Use scope terminators for nesting.
  • Use in-line Perform statement for writing 'do' constructions.
  • Use Test Before and Test After in the Perform statement while writing Do-While statements.

What are some uses of the Evaluate statement? Explore the syntax of the evaluate statement?

Ans: Some general uses of Evaluate statement are as follows.

  • Evaluate supports multi-selection control during the program execution.
  • Evaluate validate multiple conditions in a single slot.
  • Evaluate statement in COBOL is similar to Case or Switch statements of other languages.
  • Evaluate is an assessment is a case statement and can be used to replace local IFS.


EVALUATE {Expression1}  

    WHEN Cond-1  

       Statement block-1  

    WHEN Cond-2  

        Statement block-2  





    WHEN Cond-n  

        Statement block-n  

    WHEN other  

        Statement block- other  


How TEST BEFORE/AFTER works with PERFORM UNTIL explanation in COBOL?


  • With TEST AFTER, Perform articulations are handled after that condition is checked. 
  • With TEST BEFORE, Condition is checked first and then in light of the outcome Perform explanations are prepared.

What is the utilization of Linkage area in COBOL?

Ans: Linkage area is utilized as a part of COBOL if the program needs to speak with JCL by means of PARM parameter or program needs to speak with another program.

State the difference between GOBACK, STOP RUN and EXIT PROGRAM in COBOL?

Ans: The fundamental differences between GOBACK, STOP RUN, and EXIT PROGRAM in COBOL are:

  • GOBACK: It returns control to the calling program.
  • STOP RUN: It stops the present work unit and returns control to OS.
  • EXIT PROGRAM: It is utilized to leave a program that has been called by another program.

Explain Host Variables?


  • Host variables are data substances defined within a COBOL program. They are used to forward values to and receive values from a database. 
  • It can be determined under the File Section, Working-Storage Section, and Local-Storage Section or Linkage Section of a COBOL program. 
  • It can have any level number up to 48. Level 49 is reserved for VARCHAR data items. 
  • The data item name should begin with a colon (:) when a host variable name is used within an embedded SQL statement. 
  • It enables the Compiler to differentiate between host variables and tables or columns with the same name.

Host variables can be used in one of the given two ways.

Input host variables:

These are used to specify data that will be conveyed from the COBOL program to the database.

Output host variables:

These are used to hold data that is returned to the COBOL program from the database.

How to declare Host variables?

Ans: The following syntax is used to declare host variables and includes tables in the Working-Storage section:

  • EXEC SQL  
  • INCLUDE table-name  
  • END-EXEC.  
  • END-EXEC.  

. What are the file handling steps involved in COBOL programming?

Ans: A data file is a collection of relevant records and a record is a collection of relevant fields. The file handling in COBOL program involves five steps.

  • Allocation: The files used in the program should be declared in the FILE-CONTROL paragraph of environment division. The mapping with JCL DDNAME is done here. Through this statement, the file is allocated to your program.
  • Definition: The layout of the file and its attributes are defined in the FILE SECTION of DATA DIVISION.
  • Open: Dataset is connected to your program using an OPEN statement. The mode of OPEN decides the operation allowed and the initial pointer in the dataset. 
    Example: The EXTEND mode allows only to write access and the pointer is kept on the end of the file to append.
  • Process: It processes the file as per requirement, using the I-O statements provided by COBOL such as READ, WRITE, REWRITE and DELETE.
  • Close: After the processing, close the file to disconnect it from the program.

. When the JOB statement is used?

Ans: JOB statement provides the job identity to an Operating System, in the spool and the scheduler. It is the first control statement in a JCL. The available parameters in the JOB statement help the OS in allocating the right scheduler. It is also useful for analyzing the required CPU time and issuing notifications to the user.


The basic syntax of a JCL JOB statement is below.

//Job-name JOB Positional-param, Keyword-param

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. What do know about RACF in mainframes?

Ans: RACF is an acronym for resource access control facility. It is an Extreme Security Manager(ESM) for mainframe operating system. RACF stores all information about users groups and resources in profiles. A profile is a record of RACF information that has a record of RACF information which is defined by the security administrator. There are three profiles as follows.

1) User Profile:

An individual member identified by his unique id and verified using a password.

2) Group Profile

A group is a collection of RACF users who share common access requirement to protected resources or who have similar attributes within the system.

3) Resource Profile

Any information stored on a computer system such as datasets, Terminals, volumes etc. There are two types of Resouce Profiles.

  • Dataset Profiles.
  • General Resource Profiles.

. What is JCL in mainframe?

Ans: JCL in an acronym for Job Control Language. JCL is a scripting language used on IBM mainframe operating system for instructing the system for the batch job. It is a set of statements which is coded to tell the operating system about the task you would like to perform. This set of statements can also be quite large, but most jobs can be run using a very small subset.

JCL statements notify the OS on the following.

  • Where to find the required input?
  • How to process that input? 
  • What to do with the resulting output?

. How many types of JCL statements are there for a job?

Ans: There are three main types of JCL statements for all jobs:

  1. The first statement is to identify the unit of work that the operating system is to perform.
  2. The second statement is EXEC statements, depending on the number of job steps within the job.
  3. The third statement is DD statements to identify the input and output data sets.

. How is a type of file defined in the JCL that executes the COBOL program?

Ans: SORTWK01, SORTWK02, SORTWK03 ... dd Use the names in the step. The number of sorted data hang on the size of the sorted data, but at least three is required.

. Express the distinction between JES2 and JES3?


  • In JES3, the distribution of informational indexes for the means happens prior to the activity is planned for execution. 
  • In JES2, this assignment happens prior to the execution of each progression.

. Define DB2 and its Databases?


  • DB2 is a part of data management product, including database servers, developed by IBM. DB2 supports the relational model. 
  • At present days, few products have extended their functionality to support object-relational features and non-relational structure like JSON and XML. 
  • A DB2 database is a collection of different type of data like Tables, Schemas, Bufferpools, Logs, Storage groups, and Tablespaces. 
  • These data substances work together to handle database operations efficiently.

. What are the rules for DB2 programming?

Ans: The rules that are necessary for a COBOL-DB2 program are as follows:

  • All the SQL statements must be delimited between EXEC SQL and END-EXEC.
  • The SQL statements must be written in Area B.
  • All the tables that are used in a program must be declared in the WorkingStorage Section. This is done by using the INCLUDE statement.
  • All SQL statements except INCLUDE and DECLARE TABLE must belong in the Procedure Division.

. Name and explain the type of locks?

Ans: There are three types of lock, namely:

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

. Define deadlock in DB2?

Ans: When an independent process gets contended for the same or reserved resource of one another, then it is called a deadlock. The SQL codes for deadlock are -911 and the -913.

. What parameters are used to control the free space in DB2?

Ans: Free space permits the addition of new rows. There are two parameters, which are used to control the free space in DB2, they are:

  • PCTFREE: It defines the free space percentage that will be present on each page.
  • FREEPAGE: It specifies the number of pages to be loaded before leaving a page empty.
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. What is CICS?


  • CICS is an acronym for Customer Information Control System. It was introduced by IBM in 1968. 
  • It provides an MVS environment to develop and execute an online application. At present days, CICS has become the most generally used server for Internet applications.
  • It is a transaction processing system which is also called as OLTP (Online Transaction Processing Software). 
  • It is a data communication system that supports a network that has hundreds of terminals.

. What are the CICS Transactions?

Ans: CICS transactions perform multiple operations in the CICS region such as defining CICS table entries, updating records, etc. 

Few important CICS transactions of IBM are as follows.

  • CESN (CICS Execute Sign On)
  • CEDA (CICS Execute Definition and Administration)
  • CEMT (CICS Execute Master Terminal)
  • CECI (CICS Execute Command Interpreter)
  • CEDF (CICS Execute Debug Facility)
  • CMAC (CICS Messages for Abend Codes)
  • CESF (CICS Execute Sign Off)
  • CEBR (CICS Execute Temporary storage Browse)

. What is the function of DBCTL?

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

. What are VSAM Commands?

Ans: VSAM commands are used to perform operations on the datasets of VSAM. These commands are used to manipulate the datasets as per the need.

Some of the most important and useful VSAM commands are

  • Alter: It is used to modify the file attributes of the VSAM
  • Repro: It loads the data in VSAM dataset and also to copy from one VSAM dataset to another
  • Listcat: It helps in fetching the catalog details of a VSAM datasets
  • Examine: It is used to verify the structural integrity of a key-sequenced data set cluster.
  • Verify: It is applied to crosscheck and verify to fix VSAM files which may not be closed in a proper way due to error.

. Which are the main components of a VSAM?

Ans: There are three main components of a VSAM-

  1. VSAM cluster.
  2. Control Area.
  3. Control Interval.

. Please tell me what is load balancing in Citrix?


  • Load balancing is a feature that distributes client requests across servers for optimum utilization of the resources.
  • In a real-time scenario, the services are provided to a large number of clients from a limited number of servers.
  • To reduce the load on servers, the system selects certain servers.
  • These servers implement certain criteria to forward incoming requests.
  • There are virtual servers that identify the server using the load balancing criteria.
  • When the client connects to the server, the virtual server terminates the connection and initiates a new connection with the selected server.

. Name a few load evaluators that are supported in Citrix?

Ans: Load evaluators that are supported in Citrix include:

  • Scheduling
  • User Application Load
  • Server Application Load
  • Page Fault
  • CPU Utilization
  • IP range
  • Context Switches
  • Page Swap etc

. Do you know how to implement policies to streamed applications in Citrix?


  1. Open the application profile with Streaming Profiler.
  2. Move to Target and click on Edit -> Target Properties.
  3. Move to Rules Tab.
  4. Add an Ignore Registry rule that is similar to the description | CTX10352.
  5. The GPO's of the domain will be applied.
  6. Customize GPO configuration.

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. What are simple, segmented and partitioned table spaces in DB2?


Simple Tablespace:

  • Can contain one or more tables.
  • Rows from multiple tables can be interleaved on a page under the DBAs control and maintenance.

Segmented Tablespace:

  • Can contain one or more tables.
  • The tablespace is divided into segments of 4 to 64 pages in increments of 4 pages. Each segment is dedicated to a single table. A table can occupy multiple segments.

Partitioned Tablespace:

  • Can contain one table.
  • The tablespace is divided into parts and each part is put a separate VSAM dataset.

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