MainFrames Interview Questions & Answers

1. What is a mainframe?
Answer: Mainframe is a large and multi-user computer device which helps to perform TIPS per second. It has the most user-friendly bandwidth, connectivity, single-thread performance, and reliability factors.

2. What is Defragmentation and What is its advantage?
Answer: The process of combining the scattered allocated spaces for a file in a single or few contiguous areas rather than multiple areas is called defragmentation. Defragmentation reduces the number the seeks to retrieve the data.

3. What is downtime and what might be the reason?
Answer: Downtime is a very brief period that the system is not available. It is generally done for maintenance activities for the mainframe. In rare cases, it is due to a system outage.

4. Why did you choose to work with IBM Mainframe COBOL programming?
Answer: I’ve always wanted to work with computers, but I wasn’t aiming for this specific job. I saw an ad in the papers and applied and got the job. I had a bit of computer background before I applied though.

5. How scary is it to write code for a bank?
Answer: It is very scary, especially when we push changes to production which happens on Sundays. Whenever we push new changes to production, huge parts of the system has to be taken offline. One of those parts is the entire IMS. During that period anything can happen, but we have a very robust test environment so it usually goes through smoothly.

6. What is the need of running runstats in the test environment?
Answer: It is for clearing the default values from the catalog columns. Because of the columns have default values; then the result might not be an expected one. 

7. What Is Basic Difference Between “directory” And “PDS” In IBM Mainframe?
Answer: A PDS or Partitioned Data Set is a dataset containing multiple members, each of which holds a separate sub-data set, similar to a directory in other types of file systems. This type of dataset is often used to hold executable programs (load modules), source program libraries (especially Assembler macro definitions). A PDS is most somewhat analogous to a Zip file on microcomputers, except the files stored in a PDS are not compressed.

The Partitioned Data Set can only allocate on a single volume with the maximum size of 65536 tracks. Besides members, a PDS consists also of their directory. Each member can be accessed directly using the directory structure. Once a member is located, the data stored in that member is handled in the same manner as a PS (sequential) data set.

8. What will happen if both STEPLIB and JOBLIB are specified?
Answer: 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 cataloged 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 cataloged procedures.

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

9. How are composite and multiple indexes different?
 Multiple indexes is two indexes, one each for a column of the same table. A composite index is only one index, which consists of combined values of 2 columns of a table.

10. What is the function of DBCTL?
Answer: It is used to access IMS files for CICS Transactions and it is 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 a reply.

11. What is DRDA?
Answer: DRDA stands 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.

12. What is SLA?
Answer: SLA is Service Level Agreement between the customer and the vendor. It is significant in support systems wherein the terms could be like response should be given within two hours that an abend has occurred or for online systems, the system should not be down during user daytime. 

13. Explain Paging Concept in memory?
Answer: Whenever a particular data item is requested, the CPU hits primary memory or RAM first to see if the record corresponding to the data item is present on any page in primary memory. If not, it does paging and brings in the corresponding page from secondary/auxiliary memory or hard disk to primary memory and then returns the data item to the user.

14. What do you know about JCL?
Answer: JCL stands for Job Control Language. It describes the series of a batch in a mainframe system.

15. Can you name a few software running under the mainframe?
Answer: IBM is the pioneer in the mainframe computing field. Some of their 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.

16. What are the divisions in a COBOL program? Which one is the mandatory division among them?
Answer: Data division, environment division, identification division, and procedure division. Out of these, identification is the most important and mandatory division.

17. Why are you looking for a change?
Answer: Be positive towards your past/current employer. Never share any management or personal conflict instances. (Online Training) You may stress on the better opportunity, change or career growth aspects.

I am currently working as a programmer and aim to move up the career ladder in terms of growth, experience, and learning.

18. What do you know about us? Are you aware of our client base?
Answer: You have to do your homework in a detailed way before attending the interview in the organization. This will aid you to face the questions easily. If you have any doubt about any particular information, you can clarify and discuss it with the interviewer.

Your profile shows that you have jumped many organizations in five years. Please justify and how long can we expect you to work with us?
This is a tricky question. So handle it carefully. Never share any specific number or negative reasons. Rather, explain that you have had the opportunity to grow at a faster pace. Convince the interviewer that you will associate with the company for a long time.

19. What is the figurative constant in COBOL??
Answer: They are the reserved words that specify certain alphabetic or numeric constant values like zero, spaces, quotes, high and low value/s, etc.

20. Are you comfortable in COBOL or JCL?
Answer: I am specialized in COBOL mainframe. I feel that JCL has few limitations and is full of inconsistencies. But of course, I have good knowledge of JCL as well.

What was your last assignment? Discuss in detail about the roles you played.Mention the project details, the scope of work and what were your contributions in the project. Share the points of achievement which have resulted in the successful completion of the work.If you are a fresher, mention your academic assignments, projects or training that you have undergone.

21. What is a Configuration Management system, give examples?
Answer: A configuration management system is typically used in development environments to maintain versioning of the developmental code to avoid any overlay of code by different developers working on the same code. It helps maintain the integrity and consistency of the code across environments.
CHANGEMAN and ENDEVOR are examples of configuration management in the mainframe.

22. How long have you been working on mainframes?

Answer: I have over five years of experience in the field of the mainframe with specialization in COBOL.

23. What is the worst thing that you’ve seen on a day?
Answer: My co-worker forgot to add a dot to the end of a statement for a module in the most critical part of our system which we call The Cash Register. It is the part that handles all the money. The result was that the entire bank was down for 16 hours straight due to the module continuing executing statements when it actually should’ve stopped after that statement. It overloaded our systems, a self-DOS of sorts.

24. What is the binary search?
Answer: Search on a sorted array. Compare the item to be searched with the item at the center. If it matches, fine else repeat the process with the left half or the right half depending on where the item lies. (MainFrames Interview Questions)

25. How To Define A Directory And What Is The Structure And Definition For The Same?
Answer: As in DIRECTORY we can store files as well as another DIRECTORY which includes other files but PDS includes only members not another PDS inside it.

26. How To Send A Sms To A Mobile Through Mainframe VM’s?
Answer:  SMS in mainframe is the Storage Management System. I hope it has nothing to do with telephone SMS.

27. What Is Full Form Of Spool?
Answer: To spool means “to operate (an input/output device) by using buffers in main and secondary storage.” Not sure if there is any full form.

If you meant SDSF, it stands for system display and search facility.

28. Name and explain the type of locks?
Answer:  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.

29. Have you caused any huge mistakes for the bank?
Answer: have, quite a large mistake I did back in 1997 when my youngest son (thats me, the writer) just started pre-school and my parental leave was over. We have a system for saving money for retirement. Those type of bank accounts wasn’t locked back then, and the law says you cannot withdraw money from that account before you’re 55 years old. Since the accounts weren’t locked, it was possible to withdraw money if you had the bank account number, so the solution was simple; not give the customer their bank account number. I managed to screw up by modifying a module that added their bank account number to the mail that was sent out to customers. So what happened was that customers started withdrawing money (which was not taxed yet!) from their retirement savings account before they were allowed to. This triggered a huge inspection, the Swedish government stepped in, the financial inspection and the media were all over it.

30. How you can delete a record from a PS file in COBOL?
Answer: I answered something.. but they said I was not correct.. they said we can’t do this with PS file something like that. I think PS file sud be copied first into a VSAM file and then we can use file handling operation. but I forgot to mention this PS to VSAM copy process and directly answered with file handling operations. I said that we can open the file in I-O mode and then use the READ routine. 

31. If a CEO wants to see all employees of the company from an online screen.. how will be the design of the MAP from the developer point of view?
Answer: On master screen, we can allow redirection to employee screen through EIBAID concept of key triggering.. on employee screen.. certain options can be provided such as display.. edit.. delete.. and based on the checked option redirection to the employee detail display screen.

32. What Is The Meaning Of A (new, Catalog, Keep) Disposition Mean?
Answer: The meaning is that we have a fresh datasheet and it has to be allocated, the datasheet must be CTLG if all went right but to KEEP and not CTLG the datasheet when all is abended.

33. How Can We Define A Gdg?
Answer: GDG means GenerationDataGroup, for defining it we will write the command DEFINE GENERATION DATA GROUP. In the IDCAMS step, a different data set has to be defined and its DCB parameters will be used at the time when new generations are made. This is what we call a model dataset, whose ds-name has to be similar to the one of the GDG.

34. Can We Describe The Results Of Opening For Input Empty Vsam Files In A Cobol Program?
Answer: If the VSAM file didn’t have a record before it will be seen as unavailable and if we try to open it the operation will not succeed. Empty files can just be opened for output, case in which a dummy record will be written by COBOL and the file will be erased.

35. What Is The Role Of The Is Numeric Clause?
Answer: IS NUMERIC will be available for alphanumeric, packed decimal, unsigned numeric and signed numeric items. When an item is made of 0 to 9 the value returned by IS NUMERIC is True, if the item is signed then it can have 0 to 9 but also + and. (MainFrames Interview Questions)

36. What Is The Meaning, The Advantages And Which Are The Types Of Evaluate Statement?
Answer: Evaluate statement is a different way for the neste IF statements and it works by choosing from a processing actions list. To replace IF we can use When to find out if an action will be taken. Like IF, When control goes from evaluating the following statement on the application. The types of evaluating statement true and variable-name.

37. What Is Label Record Is Standard Or Omitted In File Description Of Data Division?
Answer: Label record is standard means it will use disk files. But tape files can have a standard label too. If the label record is omitted it should be a tape file without any begin and end blocks on the tape.

38. How To Handle -911 (deadlock) Error In A Db2 Program So That The Program Will Never Abend?
Deadlock timeout error occurs in the following case: If two or more programs acquired an exclusive lock on the data, which may be needed for other programs without that data which can not proceed further.

Solution: You can roll back the current unit of work for one of the programs after preset time interval for deadlocks and terminate that program.

39. What Is Use Of Linkage Section?
Answer: Linkage section is used to accept data from outside the program. either it’s parm part of Jcl or Calls from any other programs, they pass data into called program thru linkage section only.

40. How To Get The Last Record In Vsam File In Cluster? And How Can U Get The Kids File Records Into Ur Cobol Program?
Answer: Move high values to the key of the VSAM file and the issue Read next record command. Then give Readprev command. This will read the last record. In VSAM, there is one command HURBA, Using that we can read the last record If you want to know more about going to IBM RED BOOKS. You will get the solution. by using the HURBA we can get the max records by using the CKD count key data we will get the last record.

41. At what point are extension eliminators mandatory?
Answer: They are obligatory to EVALUATE articulations along with the in-line PERFORMS. Extension eliminators are announced continuously unequivocally to enhance intelligibility.

42. Express the distinction between JES2 and JES3?
Answer: In the JES3, the distribution of informational indexes for the means happens before the activity is planned for executing. While in the JES2, this assignment happens before the execution of each progression.

43. What will happen if both STEPLIB and JOBLIB are determined?
Answer: JOBLIB is a Data Definition proclamation. It decides the area of the database, which is called the EXEC articulation. JOBLIB applies to all means introduce in that entire employment. It isn’t conceivable to utilize it for detailed methodology. STEPLIB is fundamentally the same as JOBLIB. It decides the dataset within which this program exists. It applies to just one stage, not the total employment. STEPLIB could be utilized in any situation in the action step and also can likewise be utilized for detailed methodology.
In a circumstance when both the STEPLIB and JOBLIB are indicated, the JOBLIB will be overlooked by the framework.

44. Differentiate Between HDAM and the HIDAM databases?
Answer: HIDAM is a separated index file that is based on the segmented root. The HIDAM is equipped with the information of the pointers that are based on the marks of the position of the data. While on the other hand, the HDAM has separated index files, but, all the key fields of the very records that are passed through a random which places the records of a particular position of the databases.

45. Can the values of alphanumeric be moved to variable numeric?
Answer: Truly, it can be done. May confront particular information case (S0C7) blunder if the field is utilized as a part of any computation. This data answers COBOL inquiries questions identified with information development of various sort of factors.

46. Can we move Alphanumeric incentive to the Numeric field?
Answer: Indeed, we can move, and it won’t make any issue as long it is just a MOVE statement. But the program may bomb some of the time in case the field is in utilized as a part of number-crunching computations. 

47. What is the distinction amongst INCLUDE and COPY?
 A minimal distinction is there in the way they work. They both help to extend design in a program. The central contrast is INCLUDE gets extended at PRE-COMPILATION organize itself and is the motivation behind why all DCLGEN individuals are extended utilizing INCLUDE.

48. Define the necessity of run stats among the environment test?
It is used for the clearing of the different values of the catalog columns. Since this column is already equipped with default values, the result may not be as expected.

49. Define WHERE and its usage?
The clause “WHERE” isolates a row or an element during the usage of a related system.

50. What is the contrast between Delimited by Space and Delimited by Size?
Answer: In delimited by Space, Space is considered as a delimiter. In delimited by measure, add up to the size of information thing is considered as a delimiter.

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