This option (short for "Extended File I/O") relaxes the normal A-Shell regulation that any file opened for RANDOM (contiguous) access must be an exact multiple of 512 bytes in length. This might be handy if you want to use BASIC to read/write some kind of unstructured binary data. It also removes certain AMOS peculiarities which seem of dubious value, such as the automatic stripping of isolated carriage returns from strings in INPUT and INPUT LINE statements.