[G4:~/gnu/testgpc/adriaan] adriaan% cat unita.pas unit A; interface end.
[G4:~/gnu/testgpc/adriaan] adriaan% gpc -c unita.pas --ucsd-pascal unita.pas:2: error: units are an extension of Borland Pascal, traditional unita.pas:2: error: Macintosh Pascal
UCSD Pascal certainly supports units.
unita.pas:3: error: units without `implementation' part are an extension of unita.pas:3: error: traditional Macintosh Pascal
UCSD Pascal also supports units without 'implementation part', or at least Apple UCSD Pascal does.
Regards,
Adriaan van Os