IBM OS/390 User Manual

The format of the 

ASSIGN

 clause has become simpler. COBOL for OS/390 and VM

may sometimes allow the DOS/VS COBOL format but may produce unexpected
results at run-time. Refer to the 

COBOL for OS/390 and VM Compiler and

Run-Time Migration Guide for more information.

In OS/390 it is recommended that you specify 

BLOCK CONTAINS 0 RECORDS

 or 

BLOCK

CONTAINS 0 CHARACTERS

in your program. For an output file, you specify the

required information on the 

DD

 statement. If you omit the blocking information for

an output file OS/390 will supply a System Determined Blocksize (SDB). For an
input file, the information is obtained from information in the catalog and VTOC.

If you specify 

BLOCK CONTAINS n RECORDS

 and also supply the information on the

DD statement, for an output file, the

BLOCK CONTAINS n RECORDS

 takes precedence

over the DD statement information.

If you specify 

BLOCK CONTAINS n RECORDS

 for an input file, and the VTOC

information does not match, your program may ABEND or return a file status
code of 39.

DOS/VS COBOL accepts the 

LABEL RECORD IS

data-name for non-sequential files.

COBOL for OS/390 and VM does not, therefore you must change your program to
remove

LABEL RECORD IS

data-name for these files.

Under DOS/VS COBOL the 

END-OF-PAGE

 phrase may be specified without a

corresponding 

LINAGE

 clause in the file description entry.

Under COBOL for OS/390 and VM if the 

END-OF-PAGE

 phrase is specified then the

FD entry for the file must contain a 

LINAGE

 clause. Even then, you may find that

your printed page layout is not as you expect. You should use your own line
count logic in your program, making use of the 

LINAGE-COUNTER

 special register.

Under DOS/VS COBOL the 

CLOSE

file-name

WITH LOCK

 statement closed and

locked the file, and UNLOADed the tape reel or cartridge. Under COBOL for
OS/390 and VM the file is closed and locked, but only rewound, not onloaded.

Similarly, for multi-volume tape files, DOS/VS COBOL rewinds and unloads each
volume at end-of-volume. COBOL for OS/390 and VM only rewinds the tape, it
does not unload it.

Note that this behavior may be different if you use a tape management system.

VSE to OS/390 Migration Workbook