COBOL USAGE Clause Quick Reference

The USAGE clause in COBOL specifies how data is stored internally in computer memory. It determines the storage format and representation of data items, affecting storage efficiency, arithmetic performance, and data handling. Understanding USAGE is essential for optimizing COBOL programs, especially those performing extensive calculations or working with large amounts of numeric data.

USAGE Clause Syntax

The USAGE clause is specified in the data definition:

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       level-number data-name
           [PICTURE IS] picture-string
           [USAGE IS] usage-type
           [VALUE IS] value

Common USAGE types:

• DISPLAY - Character format (default)
• BINARY or COMPUTATIONAL - Binary format
• COMPUTATIONAL-3 or PACKED-DECIMAL - Packed decimal format
• INDEX - For table indexing

DISPLAY USAGE

DISPLAY is the default USAGE. Data is stored in character format (ASCII or EBCDIC), with each character occupying one byte.

Characteristics

• Human-readable in memory/storage
• One byte per character/digit
• Default if USAGE not specified
• Ideal for input/output operations
• Less efficient for arithmetic

Example

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       WORKING-STORAGE SECTION.
       01  CUSTOMER-ID         PIC 9(5) USAGE IS DISPLAY.
       01  CUSTOMER-NAME       PIC X(30) USAGE IS DISPLAY.
       01  AMOUNT              PIC 9(8)V99 USAGE IS DISPLAY.
       
       *> DISPLAY is default, so these are equivalent:
       01  AMOUNT-2            PIC 9(8)V99.  *> Also DISPLAY

BINARY / COMPUTATIONAL USAGE

BINARY (or COMPUTATIONAL, COMP) stores numeric data in binary format for efficient arithmetic operations.

Characteristics

• Efficient for arithmetic operations
• Storage size depends on PICTURE: typically 2, 4, or 8 bytes
• Not human-readable in memory
• Faster calculations than DISPLAY
• More storage-efficient for large numbers

Storage Sizes

Example

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       WORKING-STORAGE SECTION.
       01  COUNTER             PIC S9(9) USAGE IS BINARY.
       01  TOTAL-AMOUNT        PIC S9(9)V99 USAGE IS COMPUTATIONAL.
       01  QUANTITY            PIC S9(5) USAGE IS COMP.
       
       *> COMP, COMPUTATIONAL, and BINARY are equivalent
       01  AMOUNT-COMP         PIC S9(7) USAGE IS COMP.

PACKED-DECIMAL / COMPUTATIONAL-3

PACKED-DECIMAL (COMP-3) stores two decimal digits per byte, with the sign in the rightmost half-byte.

Characteristics

• Very storage-efficient for decimal numbers
• Two digits per byte (plus sign)
• Maintains decimal precision
• Commonly used in financial applications
• Not human-readable

Storage Calculation

Storage bytes = (number of digits + 1) / 2, rounded up. The "+1" accounts for the sign.

Examples:

• PIC 9(5) → (5+1)/2 = 3 bytes
• PIC 9(10) → (10+1)/2 = 6 bytes
• PIC S9(7)V99 → (7+2+1)/2 = 5 bytes

Example

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       WORKING-STORAGE SECTION.
       01  ACCOUNT-BALANCE     PIC S9(9)V99 USAGE IS PACKED-DECIMAL.
       01  PRICE               PIC S9(7)V99 USAGE IS COMPUTATIONAL-3.
       01  AMOUNT              PIC S9(5) USAGE IS COMP-3.
       
       *> COMP-3, COMPUTATIONAL-3, and PACKED-DECIMAL are equivalent

INDEX USAGE

INDEX is used for table indexing, storing positions or offsets for efficient table access.

Characteristics

• Used for table element references
• Cannot be used in arithmetic
• Manipulated with SET statements
• More efficient than numeric subscripts
• Cannot be displayed directly

Example

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       WORKING-STORAGE SECTION.
       01  TABLE-INDEX         USAGE IS INDEX.
       01  CUSTOMER-TABLE.
           05  CUSTOMER-ENTRY  OCCURS 100 TIMES
                               INDEXED BY TABLE-INDEX.
               10  CUSTOMER-ID PIC 9(5).
               10  CUSTOMER-NAME PIC X(30).
       
       PROCEDURE DIVISION.
           SET TABLE-INDEX TO 1
           SET TABLE-INDEX UP BY 1
           *> Cannot do: ADD 1 TO TABLE-INDEX

USAGE Comparison Table

Choosing the Right USAGE

Guidelines for selecting USAGE:

• Use DISPLAY for: Input/output data, text fields, data that needs to be readable, default choice
• Use BINARY for: Counters, accumulators, fields used extensively in calculations, performance-critical numeric operations
• Use PACKED-DECIMAL for: Financial amounts, decimal numbers requiring precision, storage-constrained environments
• Use INDEX for: Table subscripts, efficient table access, when using SET statements for indexing

USAGE in Calculations

When mixing USAGE types in calculations, COBOL performs automatic conversion:

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       WORKING-STORAGE SECTION.
       01  AMOUNT-DISPLAY      PIC 9(5) USAGE IS DISPLAY VALUE 10000.
       01  AMOUNT-BINARY       PIC S9(5) USAGE IS BINARY VALUE 5000.
       01  RESULT              PIC S9(6) USAGE IS BINARY.
       
       PROCEDURE DIVISION.
           *> COBOL converts DISPLAY to binary for calculation
           COMPUTE RESULT = AMOUNT-DISPLAY + AMOUNT-BINARY
           *> Result is stored in BINARY format
           DISPLAY "Result: " RESULT
           STOP RUN.

Note: Mixing USAGE types adds conversion overhead. For best performance, use consistent USAGE types (preferably BINARY) for fields in the same calculations.

Best Practices

• Use BINARY for calculation fields: Fields used in arithmetic should typically be BINARY for performance
• Use DISPLAY for I/O fields: Fields used for input/output should be DISPLAY for compatibility
• Use PACKED-DECIMAL for financial data: Financial amounts benefit from PACKED-DECIMAL's precision and efficiency
• Be consistent: Use consistent USAGE types for related fields to avoid conversion overhead
• Document USAGE choices: Document why specific USAGE types were chosen for maintainability

Common Examples

Example 1: Mixed USAGE Types

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       WORKING-STORAGE SECTION.
       01  INPUT-AMOUNT        PIC 9(8)V99 USAGE IS DISPLAY.
       01  CALC-AMOUNT         PIC S9(8)V99 USAGE IS BINARY.
       01  FINAL-BALANCE       PIC S9(9)V99 USAGE IS PACKED-DECIMAL.
       01  COUNTER             PIC S9(5) USAGE IS BINARY VALUE ZERO.
       
       PROCEDURE DIVISION.
           MOVE 1000.50 TO INPUT-AMOUNT
           MOVE INPUT-AMOUNT TO CALC-AMOUNT
           COMPUTE CALC-AMOUNT = CALC-AMOUNT * 1.1
           MOVE CALC-AMOUNT TO FINAL-BALANCE
           ADD 1 TO COUNTER
           STOP RUN.

Example 2: Financial Application

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       WORKING-STORAGE SECTION.
       01  ACCOUNT-BALANCE     PIC S9(9)V99 USAGE IS PACKED-DECIMAL.
       01  TRANSACTION-AMOUNT  PIC S9(7)V99 USAGE IS PACKED-DECIMAL.
       01  NEW-BALANCE         PIC S9(9)V99 USAGE IS PACKED-DECIMAL.
       01  RECORD-COUNT        PIC S9(5) USAGE IS BINARY VALUE ZERO.
       
       PROCEDURE DIVISION.
           MOVE 10000.00 TO ACCOUNT-BALANCE
           MOVE 250.50 TO TRANSACTION-AMOUNT
           COMPUTE NEW-BALANCE = ACCOUNT-BALANCE + TRANSACTION-AMOUNT
           ADD 1 TO RECORD-COUNT
           STOP RUN.

Explain Like I'm 5: USAGE Clause

Think of USAGE like different ways to store your toys:

• DISPLAY is like putting toys in labeled boxes you can read - easy to see what's inside, but takes more space
• BINARY is like a compact storage system - takes less space and is faster to work with, but you can't read the labels
• PACKED-DECIMAL is like a special compact box for numbers - very space-efficient and keeps numbers precise
• INDEX is like a map pointer - it tells you where things are but isn't the thing itself

Just like you choose different storage methods for different toys, COBOL uses different USAGE types for different kinds of data!

Related Concepts