Memory Size, Loaders, Entry Points, ...

The following restrictions are present in OS I/O simulation:

NOTE and POINT are only supported for Name Sequenced Record Collections.

No ALIAS support exists.

FIND type C works only in conjunction with BLDL. Use of FIND type C after NOTE will most likely abort with an addressing exception.

BLDL returns a TTRK which is the address of the name portion of the BLDL entry.

The only DCB exit code which is processed is x'05' {DCB exit}.

BSAM Variable Spanned records are only supported for unformatted writes by FORTRAN H.

BDAM search limits are not supported. The search limit is hard coded as 255 tracks or blocks.

{arcane}This is because there is no filedef interface.

BDAM variable spanned records are not supported.

BDAM and keyed BSAM Keys are limited to 252 characters. The first three characters are the TTR supplied by the program. Keyed BSAM and BDAM files are compatible.

The DCB option OPTCD=L is always forced on. Deleting records is always allowed; however, unlike OS, deleted records are not part of the file.

Either named or unnamed record collections may be used for PL/I regional-1 {COBOL Relative files}. The implementation with named record collections is sparse, and much overhead is saved by not writing unused dummy records. However, if sequential access on such files depends on the dummy records being present {such as might happen if the program counts records during a sequential read} the program will not function properly. Random access will always work correctly, as dummy records will be supplied if a non-existent record is read randomly. The implementation with unnamed record collections is dense. Thus both random and sequential access work correctly in all cases.