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COBOL SYNC and SYNCHRONIZED Clauses - Quick Reference

The SYNC and SYNCHRONIZED clauses in COBOL are used to align data fields on natural memory boundaries. They ensure optimal performance and data integrity by aligning data according to system requirements, particularly important when interfacing with other systems or optimizing for performance.

Primary Use

Align data fields on natural boundaries

Division

DATA DIVISION

Type

Data alignment clause

Status

Optional clause

Overview

The SYNC and SYNCHRONIZED clauses are used in the DATA DIVISION to specify that a data field should be aligned on natural memory boundaries. SYNC is the abbreviated form of SYNCHRONIZED. These clauses are particularly important for performance optimization and when interfacing with other systems that expect specific data alignment. They ensure that data is stored in memory in a way that optimizes access patterns and maintains compatibility with other programming languages or systems.

Syntax

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level-number field-name PIC data-type [SYNC | SYNCHRONIZED].
 
* Examples:
01  WS-ALIGNED-FIELD    PIC 9(5) SYNC.
01  WS-SYNC-FIELD       PIC X(10) SYNCHRONIZED.
01  WS-NUMERIC-FIELD    PIC 9(7)V99 SYNC.
01  WS-COMP-FIELD       PIC S9(5) COMP SYNC.
 
* In record structures:
01  CUSTOMER-RECORD.
    05  CUST-ID         PIC 9(5) SYNC.
    05  CUST-NAME       PIC X(30).
    05  CUST-BALANCE    PIC 9(7)V99 SYNC.

Practical Examples

Basic SYNC Usage

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* Basic SYNC clause example
IDENTIFICATION DIVISION.
PROGRAM-ID. SYNC-EXAMPLE.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  WS-ALIGNED-DATA.
    05  WS-FIELD-1      PIC 9(5) SYNC.
    05  WS-FIELD-2      PIC X(10).
    05  WS-FIELD-3      PIC 9(7)V99 SYNC.
    05  WS-FIELD-4      PIC X(20).
 
01  WS-NON-ALIGNED-DATA.
    05  WS-FIELD-A      PIC 9(5).
    05  WS-FIELD-B      PIC X(10).
    05  WS-FIELD-C      PIC 9(7)V99.
    05  WS-FIELD-D      PIC X(20).
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    * Initialize aligned data
    MOVE 12345 TO WS-FIELD-1
    MOVE "Test Data" TO WS-FIELD-2
    MOVE 1234567.89 TO WS-FIELD-3
    MOVE "Aligned Record" TO WS-FIELD-4
    
    * Initialize non-aligned data
    MOVE 67890 TO WS-FIELD-A
    MOVE "Test Data" TO WS-FIELD-B
    MOVE 9876543.21 TO WS-FIELD-C
    MOVE "Non-Aligned Record" TO WS-FIELD-D
    
    * Display data for comparison
    DISPLAY "Aligned Field 1: " WS-FIELD-1
    DISPLAY "Aligned Field 3: " WS-FIELD-3
    DISPLAY "Non-Aligned Field A: " WS-FIELD-A
    DISPLAY "Non-Aligned Field C: " WS-FIELD-C
    
    STOP RUN.

Explanation: This example demonstrates basic usage of the SYNC clause. The program defines two data structures: one with SYNC alignment and one without. The SYNC clause ensures that WS-FIELD-1 and WS-FIELD-3 are aligned on natural memory boundaries, which can improve performance when these fields are accessed frequently. The alignment is particularly beneficial for numeric fields that are used in calculations or comparisons.

Performance Optimization with SYNC

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* Performance optimization with SYNC example
IDENTIFICATION DIVISION.
PROGRAM-ID. SYNC-PERFORMANCE-EXAMPLE.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  WS-PERFORMANCE-DATA.
    05  WS-COUNTER      PIC 9(7) SYNC.
    05  WS-TOTAL        PIC 9(9)V99 SYNC.
    05  WS-AVERAGE      PIC 9(5)V99 SYNC.
    05  WS-MAX-VALUE    PIC 9(7) SYNC.
    05  WS-MIN-VALUE    PIC 9(7) SYNC.
    05  WS-DESCRIPTION  PIC X(50).
 
01  WS-STATISTICS.
    05  WS-RECORD-COUNT PIC 9(7) SYNC.
    05  WS-ERROR-COUNT  PIC 9(5) SYNC.
    05  WS-PROCESS-TIME PIC 9(8) SYNC.
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    * Initialize performance counters
    MOVE 0 TO WS-COUNTER
    MOVE 0 TO WS-TOTAL
    MOVE 0 TO WS-AVERAGE
    MOVE 0 TO WS-MAX-VALUE
    MOVE 9999999 TO WS-MIN-VALUE
    MOVE 0 TO WS-RECORD-COUNT
    MOVE 0 TO WS-ERROR-COUNT
    
    * Simulate processing with frequent field access
    PERFORM PROCESS-RECORDS VARYING WS-COUNTER FROM 1 BY 1 
        UNTIL WS-COUNTER > 10000
    
    * Calculate statistics
    COMPUTE WS-AVERAGE = WS-TOTAL / WS-RECORD-COUNT
    
    * Display results
    DISPLAY "Records processed: " WS-RECORD-COUNT
    DISPLAY "Total value: " WS-TOTAL
    DISPLAY "Average: " WS-AVERAGE
    DISPLAY "Max value: " WS-MAX-VALUE
    DISPLAY "Min value: " WS-MIN-VALUE
    DISPLAY "Errors: " WS-ERROR-COUNT
    
    STOP RUN.
 
PROCESS-RECORDS.
    * Simulate record processing with frequent field updates
    ADD 1 TO WS-RECORD-COUNT
    
    * Generate random value for demonstration
    COMPUTE WS-RANDOM-VALUE = FUNCTION RANDOM * 1000
    
    * Update statistics (frequent operations benefit from SYNC)
    ADD WS-RANDOM-VALUE TO WS-TOTAL
    
    IF WS-RANDOM-VALUE > WS-MAX-VALUE
        MOVE WS-RANDOM-VALUE TO WS-MAX-VALUE
    END-IF
    
    IF WS-RANDOM-VALUE < WS-MIN-VALUE
        MOVE WS-RANDOM-VALUE TO WS-MIN-VALUE
    END-IF
    
    * Simulate occasional errors
    IF WS-RANDOM-VALUE < 50
        ADD 1 TO WS-ERROR-COUNT
    END-IF.

Explanation: This example shows how SYNC can optimize performance for frequently accessed fields. The program processes records and updates various statistics counters that are marked with SYNC. Since these fields are accessed and modified frequently during processing, the SYNC alignment ensures optimal memory access patterns, reducing the number of memory cycles needed to read or write these values. This is particularly important in high-performance applications where every memory access cycle counts.

System Interface with SYNC

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* System interface with SYNC example
IDENTIFICATION DIVISION.
PROGRAM-ID. SYNC-INTERFACE-EXAMPLE.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  WS-SYSTEM-INTERFACE.
    05  WS-HEADER.
        10  WS-RECORD-TYPE    PIC X(4) SYNC.
        10  WS-RECORD-LENGTH  PIC 9(5) SYNC.
        10  WS-SEQUENCE-NUM   PIC 9(7) SYNC.
        10  WS-TIMESTAMP      PIC 9(15) SYNC.
    05  WS-DATA-PAYLOAD.
        10  WS-USER-ID        PIC 9(8) SYNC.
        10  WS-ACCOUNT-NUM    PIC 9(10) SYNC.
        10  WS-TRANSACTION-AMT PIC 9(9)V99 SYNC.
        10  WS-STATUS-CODE    PIC 9(3) SYNC.
    05  WS-TRAILER.
        10  WS-CHECKSUM       PIC 9(10) SYNC.
        10  WS-END-MARKER     PIC X(4) SYNC.
 
01  WS-INTERFACE-BUFFER      PIC X(100).
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    * Initialize system interface record
    MOVE "TXN " TO WS-RECORD-TYPE
    MOVE 100 TO WS-RECORD-LENGTH
    MOVE 1 TO WS-SEQUENCE-NUM
    MOVE FUNCTION CURRENT-DATE TO WS-TIMESTAMP
    
    * Set transaction data
    MOVE 12345678 TO WS-USER-ID
    MOVE 9876543210 TO WS-ACCOUNT-NUM
    MOVE 1234.56 TO WS-TRANSACTION-AMT
    MOVE 200 TO WS-STATUS-CODE
    
    * Calculate checksum (simplified)
    COMPUTE WS-CHECKSUM = WS-USER-ID + WS-ACCOUNT-NUM
    MOVE "END" TO WS-END-MARKER
    
    * Prepare buffer for system interface
    MOVE WS-SYSTEM-INTERFACE TO WS-INTERFACE-BUFFER
    
    * Display interface data
    DISPLAY "Record Type: " WS-RECORD-TYPE
    DISPLAY "User ID: " WS-USER-ID
    DISPLAY "Account: " WS-ACCOUNT-NUM
    DISPLAY "Amount: " WS-TRANSACTION-AMT
    DISPLAY "Status: " WS-STATUS-CODE
    DISPLAY "Checksum: " WS-CHECKSUM
    
    STOP RUN.

Explanation: This example demonstrates using SYNC for system interface compatibility. The program defines a data structure that interfaces with external systems, where specific alignment requirements are critical. The SYNC clause ensures that numeric fields are aligned on natural boundaries, which is often required when interfacing with systems written in other programming languages (like C, C++, or assembly) that expect specific data alignment. This prevents data corruption and ensures proper communication between different systems.

Memory Layout Comparison

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* Memory layout comparison example
IDENTIFICATION DIVISION.
PROGRAM-ID. SYNC-MEMORY-LAYOUT-EXAMPLE.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  WS-ALIGNED-LAYOUT.
    05  WS-ALIGNED-INT1    PIC 9(5) SYNC.
    05  WS-ALIGNED-CHAR1   PIC X(3).
    05  WS-ALIGNED-INT2    PIC 9(7) SYNC.
    05  WS-ALIGNED-CHAR2   PIC X(5).
    05  WS-ALIGNED-DOUBLE  PIC 9(9)V99 SYNC.
 
01  WS-NON-ALIGNED-LAYOUT.
    05  WS-NON-ALIGNED-INT1    PIC 9(5).
    05  WS-NON-ALIGNED-CHAR1   PIC X(3).
    05  WS-NON-ALIGNED-INT2    PIC 9(7).
    05  WS-NON-ALIGNED-CHAR2   PIC X(5).
    05  WS-NON-ALIGNED-DOUBLE  PIC 9(9)V99.
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    * Initialize data for comparison
    MOVE 12345 TO WS-ALIGNED-INT1
    MOVE "ABC" TO WS-ALIGNED-CHAR1
    MOVE 1234567 TO WS-ALIGNED-INT2
    MOVE "XYZ12" TO WS-ALIGNED-CHAR2
    MOVE 123456789.12 TO WS-ALIGNED-DOUBLE
    
    MOVE 67890 TO WS-NON-ALIGNED-INT1
    MOVE "DEF" TO WS-NON-ALIGNED-CHAR1
    MOVE 7654321 TO WS-NON-ALIGNED-INT2
    MOVE "ABC34" TO WS-NON-ALIGNED-CHAR2
    MOVE 987654321.98 TO WS-NON-ALIGNED-DOUBLE
    
    * Display memory layout information
    DISPLAY "=== Aligned Layout ==="
    DISPLAY "Integer 1: " WS-ALIGNED-INT1 " (aligned)"
    DISPLAY "Character 1: " WS-ALIGNED-CHAR1
    DISPLAY "Integer 2: " WS-ALIGNED-INT2 " (aligned)"
    DISPLAY "Character 2: " WS-ALIGNED-CHAR2
    DISPLAY "Double: " WS-ALIGNED-DOUBLE " (aligned)"
    
    DISPLAY "=== Non-Aligned Layout ==="
    DISPLAY "Integer 1: " WS-NON-ALIGNED-INT1 " (not aligned)"
    DISPLAY "Character 1: " WS-NON-ALIGNED-CHAR1
    DISPLAY "Integer 2: " WS-NON-ALIGNED-INT2 " (not aligned)"
    DISPLAY "Character 2: " WS-NON-ALIGNED-CHAR2
    DISPLAY "Double: " WS-NON-ALIGNED-DOUBLE " (not aligned)"
    
    * Demonstrate performance difference
    PERFORM MEASURE-ACCESS-TIME
    
    STOP RUN.
 
MEASURE-ACCESS-TIME.
    DISPLAY "=== Performance Measurement ==="
    DISPLAY "Note: SYNC alignment typically improves"
    DISPLAY "memory access performance, especially"
    DISPLAY "on systems that perform better with"
    DISPLAY "aligned data access patterns."

Explanation: This example compares memory layouts with and without SYNC alignment. The aligned layout ensures that numeric fields (integers and doubles) are positioned on natural memory boundaries, which can improve access performance. The non-aligned layout may result in fields being positioned at arbitrary memory addresses, which can require additional memory access cycles on some systems. This comparison helps illustrate the potential performance benefits of using SYNC alignment for frequently accessed numeric fields.

Best Practices and Considerations

Important Considerations

SYNC may increase memory usage due to padding
Use SYNC for frequently accessed numeric fields
Consider system-specific alignment requirements
Test performance impact in your specific environment
Use SYNC when interfacing with other systems

Advantages

Improved memory access performance
Better compatibility with other systems
Enhanced data integrity
Optimized for specific hardware
Reduced memory access cycles

Limitations

May increase memory usage
Performance benefits vary by system
Not always necessary for all fields
Can add complexity to data layout
May not be supported in all environments

Best Practices

• Use SYNC for frequently accessed numeric fields
• Apply SYNC when interfacing with external systems
• Test performance impact in your environment
• Consider memory usage trade-offs
• Document alignment requirements

Test Your Knowledge

1. What is the primary purpose of the SYNC clause in COBOL?

To synchronize program execution
To align data fields on natural boundaries
To synchronize file operations
To coordinate multiple programs

2. In which COBOL division is the SYNC clause typically used?

IDENTIFICATION DIVISION
ENVIRONMENT DIVISION
DATA DIVISION
PROCEDURE DIVISION

3. What is the difference between SYNC and SYNCHRONIZED?

They are exactly the same
SYNC is shorter, SYNCHRONIZED is longer
SYNC is the abbreviated form of SYNCHRONIZED
They have different alignment requirements

4. What are the main benefits of using SYNC/SYNCHRONIZED?

Reduced memory usage
Improved performance and data integrity
Better error handling
Enhanced debugging capabilities

5. When should you use SYNC/SYNCHRONIZED?

Always for all data fields
Only for numeric fields
For fields that need optimal performance or when interfacing with other systems
Only for file records

COBOL Tutorial

COBOL SYNC and SYNCHRONIZED Clauses - Quick Reference

Primary Use

Division

Type

Status

Overview

Syntax

Practical Examples

Basic SYNC Usage

Performance Optimization with SYNC

System Interface with SYNC

Memory Layout Comparison

Best Practices and Considerations

Important Considerations

Advantages

Limitations

Best Practices

Test Your Knowledge

Related Concepts

Data Types

Memory Management

Performance Optimization

System Interfaces

Data Division

Related Pages

COBOL Tutorial

COBOL SYNC and SYNCHRONIZED Clauses - Quick Reference

Primary Use

Division

Type

Status

Overview

Syntax

Practical Examples

Basic SYNC Usage

Performance Optimization with SYNC

System Interface with SYNC

Memory Layout Comparison

Best Practices and Considerations

Important Considerations

Advantages

Limitations

Best Practices

Test Your Knowledge

Frequently Asked Questions

Related Concepts

Data Types

Memory Management

Performance Optimization

System Interfaces

Data Division

Related Pages