The REEL clause is a legacy clause used in File Description (FD) entries to indicate that a file spans multiple magnetic tape reels or volumes. This clause is primarily used in tape-based file processing systems and has historical significance in mainframe COBOL applications.
REEL clause enables processing of files larger than a single tape reel can hold.
The REEL clause follows specific syntax patterns within File Description entries for tape-based files.
123456789101112131415161718192021222324* Basic REEL clause syntax REEL * With LABEL RECORDS REEL IS STANDARD * With data name reference REEL IS volume-name * Complete FD entry example FD TAPE-FILE LABEL RECORDS ARE STANDARD REEL BLOCK CONTAINS 10 RECORDS RECORD CONTAINS 80 CHARACTERS. 01 TAPE-RECORD. 05 RECORD-DATA PIC X(80). * Example with volume specification FD MULTI-VOLUME-FILE LABEL RECORDS ARE STANDARD REEL IS VOLUME-NAME BLOCK CONTAINS 50 RECORDS RECORD CONTAINS 100 CHARACTERS.
The REEL clause is typically used in FD entries for tape files.
| Clause | Usage | Storage Type |
|---|---|---|
| REEL | Magnetic tape files | Tape reels |
| VOLUME | General storage files | Any storage medium |
| Both | Multi-volume files | Multiple physical units |
1234567891011121314151617* Traditional tape file with REEL FD LEGACY-TAPE-FILE LABEL RECORDS ARE STANDARD REEL BLOCK CONTAINS 20 RECORDS RECORD CONTAINS 80 CHARACTERS. * Modern equivalent with VOLUME FD MODERN-FILE LABEL RECORDS ARE STANDARD VOLUME BLOCK CONTAINS 20 RECORDS RECORD CONTAINS 80 CHARACTERS. * Both achieve the same result * REEL is tape-specific terminology * VOLUME is medium-agnostic
REEL reflects historical tape-based storage terminology.
The REEL clause affects how files are processed, particularly in terms of volume management and error handling.
12345678910111213141516171819* File processing with REEL clause PROCEDURE DIVISION. MAIN-PROCESS. OPEN INPUT TAPE-FILE PERFORM READ-TAPE-RECORDS UNTIL END-OF-FILE CLOSE TAPE-FILE STOP RUN. READ-TAPE-RECORDS. READ TAPE-FILE AT END MOVE 'Y' TO EOF-FLAG NOT AT END PERFORM PROCESS-RECORD END-READ. * Volume switching is handled automatically * System prompts for next volume when needed * File status codes indicate volume-related events
Volume switching is typically handled automatically by the system.
| Status Code | Meaning | Action Required |
|---|---|---|
| 00 | Successful operation | Continue processing |
| 30 | Permanent error | Check file/volume |
| 35 | File not found | Verify volume mounting |
| 37 | Volume switching required | Mount next volume |
| 39 | Volume not available | Check volume status |
While the REEL clause has historical significance, understanding its modern usage and alternatives is important for contemporary COBOL development.
123456789101112131415161718192021* Legacy tape-based approach FD TAPE-FILE LABEL RECORDS ARE STANDARD REEL BLOCK CONTAINS 20 RECORDS RECORD CONTAINS 80 CHARACTERS. * Modern disk-based approach FD DISK-FILE LABEL RECORDS ARE STANDARD VOLUME BLOCK CONTAINS 20 RECORDS RECORD CONTAINS 80 CHARACTERS. * Cloud storage approach FD CLOUD-FILE LABEL RECORDS ARE STANDARD * No volume specification needed * Cloud handles volume management BLOCK CONTAINS 20 RECORDS RECORD CONTAINS 80 CHARACTERS.
Modern storage systems often handle volume management automatically.
| Scenario | Use REEL | Use VOLUME |
|---|---|---|
| Legacy tape systems | Yes | No |
| Modern disk systems | No | Yes |
| Cloud storage | No | Optional |
| Mixed environments | For tape | For disk |
| New development | Rarely | Preferred |
Following these best practices ensures effective use of the REEL clause in both legacy and modern COBOL applications.
| Migration Step | Action | Consideration |
|---|---|---|
| Assess storage type | Determine if tape or disk | Choose appropriate clause |
| Update FD entries | Change REEL to VOLUME if needed | Maintain functionality |
| Test volume handling | Verify volume switching works | Ensure no regressions |
| Update documentation | Reflect new storage approach | Keep documentation current |
| Train operators | Update operational procedures | Ensure smooth operations |
| Usage | Syntax | Example |
|---|---|---|
| Basic REEL | REEL | REEL |
| With LABEL RECORDS | REEL IS STANDARD | REEL IS STANDARD |
| With data name | REEL IS data-name | REEL IS VOLUME-NAME |
| In FD entry | FD file-name REEL | FD TAPE-FILE REEL |
| Modern alternative | VOLUME | VOLUME |
1. What is the primary purpose of the REEL clause in COBOL?
2. In which context is the REEL clause most commonly used?
3. What does the REEL clause indicate about a file?
4. What is the relationship between REEL and LABEL RECORDS clauses?
5. Which of the following is NOT a valid REEL specification?
Understanding the VOLUME clause for modern storage systems.
Complete guide to File Description entries.
Using LABEL RECORDS with REEL clause.
Understanding different file organizations.
Working with sequential files in COBOL.