Mainframe Interview Questions and Answers for 2025

We can, in fact, move, and doing so won't cause any problems as long as the phrase we use is simply "MOVE." However, if the field is used as a component of number-crunching calculations, the application may fail to function properly on occasion.

If the name of the programme is explicitly referenced in the CALL explanation, then the call is deemed to be static. If, on the other hand, a working storage variable is referenced in the CALL explanation, then the call is considered to be dynamic.

DBD restricts access to only one item at a time for security reasons. It is argued that lock contention has occurred when many objects concurrently request permission to execute.

It is kept in the last nibble. For instance, if our number is 100, it will store hex 0C in the final byte; if our number is 101, it will store hex 1C; if our number is 102, it will store hex 2C; if the number is -101, it will store hex 1D; and so on and so forth.

While it is possible to keep files inside a DIRECTORY in addition to another DIRECTORY that also contains files, a PDS only includes its own members and does not include any other PDSs.

One of the most frequently asked Mainframe interview questions, be ready for it.

• Using JCL, we can remove as well as create a large number of data sets, VSAM Clusters (which stand for "Virtual Storage Access Method"), and GDGs (which stand for "Generation Data Groups"). 
• It is possible to do file comparisons using distinct PDS (Partitioned Data Set) members using it. 
• We can combine and organize a wide variety of data files with it. 
• Additionally, it is able to execute and compile batch-based applications, which are pre-scheduled programmes that are assigned to run on a computer without any further intervention from the user. 
• It is simple to make changes to, JCL is also simple to understand for newcomers. 
• In addition to this, it offers a variety of useful tools, such as IEDCOPY, IDCAMS, and other similar programmes, which make it simpler and more practical to carry out a variety of activities. 

Any parameter that changes with each iteration of a programme should, in general, be regarded as a symbolic parameter. It is possible to get more flexibility in the method by employing symbolic parameters. It won't be necessary to make adjustments to the technique each and every time there is a seemingly little but ongoing change at a certain location.

In the case of symbolic parameters, the string of 1 to 7 alphabetic letters is preceded by an ampersand sign (&). After the ampersand (&), you are required to type in a letter from the alphabet. In JCL statements, symbolic parameters are only allowed to appear in the operand field; they are not allowed anywhere else. 

JCL statements do not allow symbolic parameters to appear in the name or operation fields. In the event that more than one symbolic parameter is supplied to a PROC or EXEC statement, only the first one will be used.

Temporary datasets are datasets (files that store one or more records) that are only required for the length of the task and are erased once the project is over. These datasets are deleted after the job is finished. They need storage just for the period of the work, and as soon as the project is over, the files may be erased.

These datasets are often expressed using the notation DSN=&&name, or else they are left unspecified in terms of a DSN. Using them, we are able to transmit the results of one phase to the subsequent steps of the same project. 

By specifying TYPERUN=SCAN on a job card or by executing JSCAN, it is possible to examine JCL syntax without actually running the programme. The TYPRUN command is used to request specific job processing, such as checking or scanning a task for syntax mistakes. 

This is one example of what may be done with this command. SCAN examines the code for any syntax mistakes but does not carry out the task itself. In every other case, JSCAN is able to verify the syntax of a JCL without actually executing it. 

A task timeout happens if a programme takes more time to complete than the allotted maximum amount of time for the specific category that was chosen. An "S322 abend" is the common name for this kind of error. Due to the circular mistakes that have occurred, the application cannot be finished in this scenario. 

If the amount of data that has to be processed by the programme is very large and requires a longer period of time to accomplish its goals, the TIME parameter might be specified as TIME = 1440. 

A Mainframe basic interview question, be prepared to answer this one. CICS stands for Customer Information Control System. All of the administration of IBM's online transactions are brought within the purview of this sort of system. CICS is for computer integrated circuit system, and it refers to a mode of processing that is mostly launched by the use of a single request that may also influence one or more objects. 1969 was the year that saw the beginning of the CICS's establishment.

PPT is an abbreviation that mostly refers to the Processing Programming Table in the CICS. The PPT includes information such as the name of a programme, the names of its Mapsets, the task usage counter, the language, the size, the primary storage location, and so on.

• TCP
  • TCP stands for Terminal Control Protocol. 
  • TCP is used for terminal message reception. 
  • It maintains hardware communication needs. 
  • It requests that CICS begin the duties. 
• KCP
  • KCP stands for Task Control Program. 
  • KCP is used to regulate the execution of jobs as well as their associated attributes at the same time. 
  • It addresses all aspects of multitasking. 
• PCP
  • PCP stands for Program Control Program. 
  • PCP is a software that is used to find and load programmes for execution. 
  • It transfers control across programmes and then restores control to the CICS. 
• FCP
  • File Control Program (abbreviated as FCP) is a common acronym for this kind of software. 
  • Application developers rely on FCP to do tasks like reading, writing, and modifying files. 
  • For the sake of consistent data storage and update operations, it retains exclusive authority over the records. 
• SCP
  • Storage Control Program is an abbreviation for this. 
  • Within a CICS area, it regulates storage allocation and deallocation. 

• A transaction is a one-of-a-kind identifier that is often used to begin or carry out a certain activity. 
• A transaction is the kind of thing that the four-character entry is for, and there won't be any duplication permitted, especially in the names of the transactions. 
• It is possible for a transaction to be initiated simultaneously from distinct systems, but not from the same systems themselves. 
• When a transaction is performed, there will often be one or more mappings to the programme that fundamentally need to be carried out in order for the transaction to be completed successfully. 

The acronym "FCT" refers to the "File Control Table." It is necessary for the file control table to have entries for each and every kind of VSAM file that is used by the CICS applications. The FCP stands for "film control programme" and is mostly a reference to the FCT.

The FCT includes the following fields: ACCMETH, which stands for "data access method," DATASET, which stands for "dataset name," FILE, which stands for "file name," SERVEQ, which stands for "operation needs to be performed on," FILESTAT, which stands for "file initial status," BUFND, which stands for "number of data numbers," and BUFNI, which stands for "number of index buffers." 

VSAM (Virtual Storage Access Method) is both a form of dataset and an access method for managing a variety of dataset types. As an access technique, VSAM provides higher functionality, performance, and adaptability than conventional disc access methods. In VSAM, records are stored in a format that is incomprehensible to other systems. VSAM arranges data on mainframe systems into files. This is one of the most prevalent high-performance file access mechanisms used in operating system variants such as MVS, z/OS, and OS/390.  

With VSAM, businesses may arrange file records in physical order (the order in which they were entered) or logical order using a key (such as the employee ID number) or based on their relative record numbers on DASD (Direct Access Storage Device). In VSAM, record lengths may be fixed or flexible. 

Integrated Data Cluster Access Method Services is what "IDCAMS" stands for in its acronym form. The IDCAMS Utility makes it simple to perform manipulations on VSAM datasets. It is possible to use it to create new VSAM datasets, delete existing ones, and change existing ones.

 In contrast to non-VSAM data sets, VSAM data sets are structured differently. The groupings of records that make up the VSAM data sets are organised into CI categories (control intervals). The control interval is a predetermined section of storage space where VSAM saves its records. This section is always the same size. 

A VSAM record may be no longer than one cylinder in length at most. Records may be organised in VSAM according to the index key, the relative record number, or the relative byte address, depending on which one is most relevant.

The order in which entries were added to the dataset is the order in which they are stored in ESDS files. The records may be located using their physical address, which is also referred to as their RBA (Relative Byte Address). Assuming that each record in an ESDS dataset has sixty bytes, the RBA of the first record would be zero, the RBA of the second record would be sixty bytes, the RBA of the third record would be one hundred twenty bytes, and so on.  

Access to records may be made in a sequential fashion using RBA, which is also known as addressed access. The data is saved in the same order as it was input into the system. The most recent records are appended to the end of the list. The ESDS dataset does not allow for the deletion of records; nevertheless, such records may be tagged as inactive. The length of records in an ESDS dataset may either be variable or fixed. 

VSAM Share Options are what decide who may see certain VSAM datasets. Using these controls, you may provide varying degrees of access to a single VSAM dataset for various users/jobs. SHAREOPTS is the name of the parameter used in the DEFINE statement (a,b). Two or more users/jobs on the same MVS system may share a file using the cross-region share option denoted by letter a, whereas two or more users/jobs on separate MVS systems can use the cross-system share option denoted by letter b.

Typically, this is the SHAREOPTS value (2 3). If the value for cross-region is 2, then numerous users may work on the file at once, but only one can be an updater. If the cross-system parameter is set to 3, then any number of jobs or users may utilise this file for processing (VSAM does not ensure integrity).

The DBKEY is what is used in order to identify the record instance inside the database at a certain address position. It is the practise of using line numbers in conjunction with page numbers. A four-byte address consists of the numbers 3 and 1, where 3 represents the page number and 1 represents the line number. Pages are always distinct in each and every one of the sections. 

• Direct Access: The record is persisted whenever the DBKEY is given, provided that the place in question is vacant. 
• Sequential Access: This kind of access saves each instance of a record one after the other and line by line. 

IDMS/R scans through all the available records in an area in physical sequence, while performing an area. The order of records retrieval will have little bit of relationship to some logical sequence of records. Area sweeps are utilized when all the records need to be retrieved in an area irrespective of the order. Extraction jobs are commonly implemented by Area sweeps.

One of a Kind is the complete abbreviation for OOK. IDD's meta schema is included inside this document. During the course of the installation process, the IDD meta schema is generated. There is a unique name assigned to each database, and each OOK record will have its own unique location to store the database name as well as other information.

Junction record is a form of record for members. Allows for many-to-many relationships to be established between its two owner records. For instance, in the database of a corporation, the record for DEPARTMENT serves as a junction record for the EMPLOYEE record type and the PROJECT record type.

Files are used as the primary organisational mechanism for databases.

• Mapping the files to the sections that have already been formatted is done.
• Each of the regions is broken down onto a page.
• The physical blocks that make up the disc are represented by each page.
• The database administrator (DBA) sets the records that are to be kept in each area as well as how those records are to be stored, and then allots a certain number of pages in a file for that area.
• In order to cut down on the amount of I/O that is needed, free space is only monitored globally across all of the pages.

The z/OS system uses JCL to handle work by specifying which application should be run, allocating resources, etc. A job is a job description in the broad sense. The z/OS system utilizes the Job Entry Subsystem (JES) to manage the input, scheduling, processing, and output of tasks.

Input Phase: The tasks are input during the input phase using input devices such as remote terminals, card readers, job entry networks, etc. For job submission, JES2 can also read instructions and control statements from internal readers that may be utilised by other applications. 

JES2 assigns a job identifier to each job as it reads the input stream, and then writes the job's JCL, control statements, SYSIN data, and so on to spool data sets on DASD. The datasets may be accessed directly by the spool, allowing for simultaneous task execution, and the spool can be used as a temporary storage space for unfinished operations. In the future, JES2 will choose tasks from this spool to run. 

Conversion Phase: In the conversion process, a converter software is used to examine each JCL command and validate the syntax of the resulting code. 

JES may also check for the presence of procedure calls in JCL. A convertor is a programme that takes job control language (JCL) files, combines them with other JCL files using a procedural library like SYS1.PROCLIB, and then transforms the resulting composite JCL to internal text that is saved in a spool. 

When JES2 detects a mistake during this transformation, it generates and stores an error message in a buffer for further processing. 

If there are no problems with the work, it will be placed in a queue according to its class priority. 

Execution Phase: Initiators are begun during this period, either automatically or with the help of an operator, when the system is first turned on. When everything is set, the initiator will send a request to JES2 to begin the work. 

Based on the priority set for the order of execution, JES2 chooses the work and sends it to the initiator. 

The control blocks are constructed from the internal text generated by the initiator, which is then invoked by the interpreter. It also allots the necessary assets to carry out the task at hand. 

According to the instructions in the JCL EXEC statement, once enough resources are made available, the application will begin running. 

Output Phase: After the programme has been executed, system messages are sent to the user through the output phase. JES2 evaluates the work's output characteristics against the specifications and places the job in a queue for printing or punching. Records that need to be processed locally or remotely may be stored in this queue, which is termed an output queue. 

Jobs are prepared for the purge phase and delivered to the purge queue after the output processing is finished. 

Purge Phase: After a task has been processed, its unused resources and spool space are "purged" when JES2 retrieves them from the purge queue. When the purge is complete, the system will notify the operating system. 

Making use of the RETURN-CODE keyword, which may be used for transferring information to the JCL from the COBOL programme, is one way in which this objective might be accomplished. It is something that we may utilize to determine the results of any process.

In most circumstances, the activity of the programme will return the value 0, 4, 8, or 12 depending on whether or not it was successful. By using this keyword, which also guarantees that the information is transmitted from COBOL to JCL, we are able to make the necessary changes.

The COBOL programme is responsible for handling the internal sorting, and it does so by using an input file, a work file, and an output file. When doing any sort of processing in this environment, it is necessary to recompile the COBOL programme. Internal Sort makes use of two distinct syntaxes, namely: 

The USING and GIVING kinds do not need any further processing of the file. 

• INPUT PROCEDURE and OUTPUT PROCEDURE sorts are able to manipulate data either before or after the sorting process. 
• The external sort does not rely on COBOL; instead, it makes direct use of the SORT tool and relies on JCL in conjunction with the PGM=SORT command to complete the process.

When information is requested from the computer's memory, the central processing unit (CPU) first accesses the main memory, also known as random access memory (RAM), and checks to see whether the information being sought is stored on the memory page in question. In the event that it is absent, the central processing unit will execute paging on the secondary memory, which means that it will read data from the hard drive-in equal chunks of memory that are referred to as pages.

When it comes to paging, a frame represents a single page of physical memory, but such pages do not need to be physically contiguous with one another. This guarantees that memory can be accessed more quickly, and that data can be retrieved from secondary memory more quickly.

When two or more mainframe programmes try to gain an exclusive lock on the same resource at the same time, deadlock results because the programmes are unable to proceed until the data is accessible. In the event that the error happens, we have the ability to roll back the currently active work unit of any one of the programmes after a defined preset deadlock time period, which will result in the programme being terminated.

The necessary operations may be carried out by using the IEBEDIT software. It provides choices to either Include or Exclude the stages that need to be completed. Utilizing the appropriate COND Parameters is necessary to accomplish this goal if the number of stages in the PROC is to be reduced.

If there is a specific key that has to be used as the starting point for the reverse process, then that key should be entered into the RIDFLD field. 

• The Start Browse Command Should Be Issued 
• Send out a READNEXT COMMAND, which really begins the reading process from the key that was supplied. 
• Now, issue the READPREV command, and put this read prior into a loop, continuing the loop until the necessary condition is satisfied. 
• Move LOW-VALUES into the Key field and continue with the same approach as described above if it is necessary to read the file in reverse order starting from the most recent entries and working backwards. 

In this phase, we are able to make use of SORTWK01, SORTWK02, and so on. There must be a minimum of three datasets, but in general, the number of sort datasets is related to the magnitude of a dataset that must be sorted. 

During the sorting process, the following files are utilised: -  

Input File: It is necessary to declare the FD entry for the input file in the FILE SECTION. 

Work-file: This is a temporary file that will be used while the sorting procedure is being carried out. It is recommended that the SD (Sort Description) entry for the file be specified in the FILE SECTION. 

Output File: File that will have sorted entries written to it; known as the output file. 

Basic syntax:  

SORT work-file ON {ASCENDING/DESCENDING} 
KEY sd-rec-key-1 [,sd-rec-key-2]… 
USING input-file 
GIVING output-file. 
Format of SD entry: 
SD work-file 
[RECORD CONTIANS integer CHARACTERS] 
[DATA RECORD IS file-rec-1] 

Using REDEFINES, the answer is that it is indeed feasible to do so. It is essential for us to bear in mind that redefining does nothing more than guarantee that fields begin in the same spot.

01 WS-TOP PIC X(100) 
01 WS-TOP-DOUBLE REDEFINES WS-TOP PIC X(200)

During the SORT phase, we are able to specify the names of the SYSIN and SYSOUT datasets. In order to transfer data from one dataset to another, we need to make sure that the sort card includes the notation SORT FIELDS = COPY.

We are able to make advantage of RD parameter in the JOB/EXEC statement by stating in the SCHEDxx component of the parmlib library of the IBM system for what abend codes RESTART needs to be done.

The maximum amount of data that can be sent by COMMAREA is 32 kilobytes. If additional data has to be transmitted, then TSQs may be utilised to hold the data that is more than 32 kilobytes. Obtain storage by using the GETMAIN command, and then provide the address of the acquired data in the COMMAREA field. 

Using Channels and Containers, which is a novel strategy that was introduced in the CICS transaction Server version 3.1. This allows for more flexibility while transmitting bigger volumes of data.

COMMAREA is one of the essential functions that CICS offers, and it is used for the purpose of passing data between two programmes that are participating in a transaction or between two transactions that are taking place on the same terminal. It is a unique kind of user storage that can only hold up to 32 kilobytes of data at a time. However, 24k is the maximum suggested data size that may be sent.

I have the option of using the NOTIFY statement, which informs the user when the process has been finished and provides the return code. 

NOTIFY = userid to whom status needs to be notified  

In case my DB2 table has an identity column, then we can use the indexnum as follows:

Update Table SET COLUMN_NAME=XXX where indexnum < 101