Understanding the mainframe environment is crucial for COBOL developers, as most enterprise COBOL applications run on mainframe systems. The IBM System z (z/OS) platform dominates the mainframe landscape and provides the robust, scalable environment needed for mission-critical business applications.
IBM System z servers with processors, memory, and I/O subsystems
MVS-based OS with job management, memory management, and I/O control
Transaction processing, database management, and online systems
Business logic and application processing layer
COBOL development can occur in various environments, from traditional mainframe setups to modern distributed systems. Understanding these environments helps developers choose the right tools and approaches for their projects.
| Aspect | Mainframe | Distributed |
|---|---|---|
| Development Speed | Slower initial setup, faster for large-scale | Faster prototyping and iteration |
| Runtime Performance | Superior for high-volume processing | Good for moderate workloads |
| Scalability | Vertical scaling excellence | Horizontal scaling flexibility |
| Debugging Tools | Powerful, but specialized | Modern, intuitive interfaces |
| Cost Structure | High fixed, low variable costs | Lower fixed, variable scaling costs |
| Skills Required | Specialized mainframe knowledge | Modern development practices |
TSO/ISPF (Time Sharing Option/Interactive System Productivity Facility) is the traditional and still widely-used development environment on z/OS mainframes. Understanding TSO/ISPF is essential for mainframe COBOL developers.
12345678LISTCAT - List catalog entries LISTDS - List dataset information EDIT - Edit datasets SUBMIT - Submit JCL jobs STATUS - Check job status RECEIVE - Receive transmitted datasets TRANSMIT - Send datasets to other users ALLOCATE - Allocate new datasets
ISPF provides a menu-driven interface built on top of TSO
123456789101112131415161718ISPF Primary Option Menu Option ===> 0 Settings Terminal and user parameters 1 View Display source data or listings 2 Edit Create or change source data 3 Utilities Perform utility functions 4 Foreground Interactive language processing 5 Batch Submit job for language processing 6 Command Enter TSO or Workstation commands 7 Dialog Test Perform dialog testing 8 LM Utilities Perform library administrator utility functions 9 IBM Products IBM program development products 10 SCLM Software Configuration Library Manager 11 Workplace ISPF Object/Action Workplace C Changes Display summary of changes for this session T Tutorial Display information about ISPF X Exit Terminate ISPF using log and list defaults
The primary tool for editing COBOL source code
12345678910I - Insert line(s) D - Delete line(s) R - Repeat line(s) M - Move line(s) C - Copy line(s) XX - Exclude line(s) F - Show excluded lines =X - Show excluded line numbers UC - Uppercase LC - Lowercase
12345678FIND string - Search for text CHANGE old new - Replace text SAVE - Save dataset CANCEL - Cancel without saving COPY member - Copy another member MOVE member - Move text from member SUBMIT - Submit current member as JCL NUM ON/OFF - Toggle line numbers
View-only access to datasets and output
Essential utilities for COBOL development
Use ISPF Edit (Option 2) to create/modify COBOL programs
Submit JCL to compile COBOL source using ISPF (3.4 → S)
Use SDSF or ISPF Browse to view compilation results
Fix errors, test program execution, repeat as needed
1234567891011121314151617181920/* Step 1: Access ISPF Edit */ Command ===> TSO ISPF -> Select Option 2 (Edit) -> Specify dataset: USERID.COBOL.SOURCE(HELLO) /* Step 2: Enter COBOL code */ 000100 IDENTIFICATION DIVISION. 000200 PROGRAM-ID. HELLO. 000300 PROCEDURE DIVISION. 000400 DISPLAY "Hello from mainframe COBOL!". 000500 STOP RUN. /* Step 3: Save and submit for compilation */ Command ===> SAVE Command ===> SUBMIT /* Step 4: Check job output using SDSF */ Command ===> SDSF -> Select job output to view compilation results
Understanding the distinction between batch and online processing is crucial for COBOL developers, as these different execution models require different programming approaches and considerations.
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354IDENTIFICATION DIVISION. PROGRAM-ID. PAYROLL-BATCH. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT EMPLOYEE-FILE ASSIGN TO EMPIN. SELECT PAYROLL-FILE ASSIGN TO PAYOUT. DATA DIVISION. FILE SECTION. FD EMPLOYEE-FILE. 01 EMPLOYEE-RECORD PIC X(100). FD PAYROLL-FILE. 01 PAYROLL-RECORD PIC X(150). WORKING-STORAGE SECTION. 01 WS-EOF-FLAG PIC X VALUE "N". 01 WS-RECORD-COUNT PIC 9(7) VALUE ZERO. 01 WS-TOTAL-SALARY PIC 9(11)V99 VALUE ZERO. PROCEDURE DIVISION. MAIN-PROCESS. OPEN INPUT EMPLOYEE-FILE OUTPUT PAYROLL-FILE. PERFORM READ-EMPLOYEE. PERFORM PROCESS-RECORDS UNTIL WS-EOF-FLAG = "Y". DISPLAY "Records processed: " WS-RECORD-COUNT. DISPLAY "Total salary: " WS-TOTAL-SALARY. CLOSE EMPLOYEE-FILE PAYROLL-FILE. STOP RUN. PROCESS-RECORDS. PERFORM CALCULATE-PAY. PERFORM WRITE-PAYROLL. PERFORM READ-EMPLOYEE. READ-EMPLOYEE. READ EMPLOYEE-FILE AT END MOVE "Y" TO WS-EOF-FLAG NOT AT END ADD 1 TO WS-RECORD-COUNT END-READ. CALCULATE-PAY. * Complex payroll calculations here CONTINUE. WRITE-PAYROLL. WRITE PAYROLL-RECORD.
Customer Information Control System
Information Management System
Interactive development
12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061IDENTIFICATION DIVISION. PROGRAM-ID. CUSTINQ. DATA DIVISION. WORKING-STORAGE SECTION. 01 WS-COMMAREA. 05 WS-CUSTOMER-ID PIC X(10). 05 WS-FUNCTION-CODE PIC X(2). 05 WS-RESPONSE-CODE PIC X(2). 01 WS-CUSTOMER-RECORD. 05 CUST-ID PIC X(10). 05 CUST-NAME PIC X(30). 05 CUST-BALANCE PIC S9(9)V99 COMP-3. LINKAGE SECTION. 01 DFHCOMMAREA PIC X(20). PROCEDURE DIVISION. MAIN-PROCESS. * Move communication area data MOVE DFHCOMMAREA TO WS-COMMAREA. * Validate input IF WS-CUSTOMER-ID = SPACES MOVE "01" TO WS-RESPONSE-CODE PERFORM SEND-ERROR-SCREEN EXEC CICS RETURN END-EXEC END-IF. * Read customer record EXEC CICS READ DATASET("CUSTMAST") INTO(WS-CUSTOMER-RECORD) RIDFLD(WS-CUSTOMER-ID) RESP(WS-RESPONSE-CODE) END-EXEC. * Process based on response EVALUATE WS-RESPONSE-CODE WHEN DFHRESP(NORMAL) PERFORM SEND-CUSTOMER-SCREEN WHEN DFHRESP(NOTFND) PERFORM SEND-NOTFOUND-SCREEN WHEN OTHER PERFORM SEND-ERROR-SCREEN END-EVALUATE. EXEC CICS RETURN END-EXEC. SEND-CUSTOMER-SCREEN. * Format and send customer information CONTINUE. SEND-ERROR-SCREEN. * Send error message to terminal CONTINUE. SEND-NOTFOUND-SCREEN. * Send customer not found message CONTINUE.
| Aspect | Batch Processing | Online Processing |
|---|---|---|
| Execution Mode | Sequential, non-interactive | Interactive, real-time |
| Data Volume | Large volumes, bulk processing | Small transactions, individual records |
| Response Time | Hours to complete | Seconds or less |
| Resource Usage | High CPU, I/O intensive | Efficient resource sharing |
| Error Handling | Restart/recovery procedures | Immediate error reporting |
| Development Complexity | Simpler logic flow | Complex state management |
| Scheduling | Predetermined schedules | On-demand execution |
In the mainframe environment, COBOL programs don't exist in isolation. They work in conjunction with JCL (Job Control Language) for execution control and various data management systems for data access and manipulation.
Job Control Language (JCL) is the command language that tells the z/OS operating system how to run batch jobs, including COBOL programs.
12345678910//PAYROLL JOB (ACCT),"PAYROLL PROCESSING",CLASS=A,MSGCLASS=X //STEP1 EXEC PGM=PAYROLL //STEPLIB DD DSN=PROD.LOADLIB,DISP=SHR //EMPIN DD DSN=PAYROLL.EMPLOYEE.MASTER,DISP=SHR //PAYOUT DD DSN=PAYROLL.OUTPUT.FILE, // DISP=(NEW,CATLG,DELETE), // UNIT=SYSDA,SPACE=(TRK,(100,10)), // DCB=(RECFM=FB,LRECL=150,BLKSIZE=15000) //SYSOUT DD SYSOUT=* //SYSPRINT DD SYSOUT=*
This JCL job runs the PAYROLL COBOL program, allocating input (EMPIN) and output (PAYOUT) files, with system output directed to SYSOUT.
123456789ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT EMPLOYEE-FILE ASSIGN TO EMPIN. SELECT PAYROLL-FILE ASSIGN TO PAYOUT. SELECT REPORT-FILE ASSIGN TO RPTOUT.
1234567//EMPIN DD DSN=EMP.MASTER,DISP=SHR //PAYOUT DD DSN=PAY.OUTPUT, // DISP=(NEW,CATLG), // SPACE=(TRK,(50,5)) //RPTOUT DD DSN=PAY.REPORT, // DISP=(NEW,CATLG), // SPACE=(TRK,(10,2))
1234567891011* Read from input file, process, write to output file PROCEDURE DIVISION. MAIN-PROCESS. OPEN INPUT TRANSACTION-FILE OUTPUT MASTER-UPDATE-FILE. PERFORM READ-TRANSACTION. PERFORM PROCESS-TRANSACTIONS UNTIL EOF-FLAG = "Y". CLOSE TRANSACTION-FILE MASTER-UPDATE-FILE. STOP RUN.
12345678910111213* Embedded SQL in COBOL EXEC SQL SELECT CUSTOMER_NAME, ACCOUNT_BALANCE INTO :WS-CUSTOMER-NAME, :WS-ACCOUNT-BALANCE FROM CUSTOMERS WHERE CUSTOMER_ID = :WS-CUSTOMER-ID END-EXEC. IF SQLCODE = 0 PERFORM PROCESS-CUSTOMER-DATA ELSE PERFORM HANDLE-SQL-ERROR END-IF.
1234567891011121314* Process multiple related files PROCEDURE DIVISION. MAIN-PROCESS. OPEN INPUT CUSTOMER-FILE TRANSACTION-FILE OUTPUT REPORT-FILE. PERFORM READ-CUSTOMER. PERFORM READ-TRANSACTION. PERFORM MATCH-PROCESS UNTIL CUSTOMER-EOF = "Y" AND TRANSACTION-EOF = "Y". CLOSE CUSTOMER-FILE TRANSACTION-FILE REPORT-FILE. STOP RUN.
COBOL programs act as the processing engine, reading from various data sources, applying business rules, and producing outputs for downstream systems.