Rules for Linkage Section

1. The maximum size of the data that can be passed from one program to another program is 64K.
2. The maximum size of the data that can be passed through the PARM operand is 100 bytes.
3. Unique data name must be given to the variable in the Linkage Section for levels 01 to 77.
4. Here, the data item or the variable should not consist of any values in the VALUE clause.
5. Each 01-level item should be defined or included in the PROCEDURE DIVISION USING the data-item name.

The linkage Section in COBOL is used to declare the variables and it is used in calling the variable from another program. It is used in calling the variable or data from the called program by using the CALL statement. 

The linkage Section helps in sending the data to the calling program or receiving the data from the calling program. The declaration of a variable to the Linkage section is nothing but the group, individual or elementary variables. The linkage section is also used in receiving the data from JCL a  PARM operand (PARM is nothing but a parameter keyword).

Syntax :

DATA DIVISION.

LINKAGE SECTION.

[variable declaration]