The Linkage Section is used to define data items that are passed from a calling program.
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- Each level 01 and 77 data item described in Linkage must be uniquely named.
- Subordinate data names need not be unique if they can be made unique through qualification.
- Each level 01 and 77 data item declared in Linkage should be named in a USING phrase of the Procedure Division header. Data
items that are REDEFINES of other data items should not be named, however.
- There is a limit of 255 level 01 Linkage data items per program. There is no limit for the number of subordinate items allowed
for each of these level 01 items.
There are two runtime configuration variables that relate to linkage items:
for specifying parameter size-matching testing; and
that perform address optimizations on each Linkage item individually.