3. COBOL files

The most common type of file is the sequential file, where items or records are arranged in the order in which they were written. In general, the order is determined by a designator (REF line 34 for the INPUT item in the FILECTU file described on lines 30 to 35).

Once a file has been created, its items can only be reread in this order, one after the other, and possibly rewritten after modification. If you wish to process the file in a different order, you must first sort it on another code (a service code, for example).

If you want to access a particular item, you have to read all the items preceding it, which can be very time-consuming for a file containing several million items. It is therefore unthinkable to use a sequential file for a transactional application with random access to records.