In the current version of COBOL is none. In the older versions, the compiler handled 77 level as a single value and the “01” as possible subdivided field.
Level 01 and Level 77 items are aligned on word boundaries. But I seem to remember (way back when) that Level 77 items could not be stomped on by accident. And I think nowdays that point is moot.
Level Number 77 in COBOL/400.
1. The Level number 77 cannot be subdivided into other items. This is considered to be an elementary item. Also, it must begin in AREA A.
2. Also, Level Number 77 is used for LIKE Clause. For LIKE Clause, we can specify the level number from 1-49 or 77.
Sample Code: 01 FIELD1 PIC X(5) VALUE IS ‘ABC’.
77 FIELD2 LIKE FIELD1 VALUE ‘BCD’.
Hope this helps.