Abstract: A device such as a cassette recorder of a computer has a wall portion formed with a loading aperture for introduction of standard-type objects, such as a magnetic-tape cassette or a cassette for an optical or magnetic disc. To prevent damage or incorrect operation, the device includes a blocking mechanism which blocks the introduction of objects having a smaller width and/or height. A spring urges a partially inserted object in a direction parallel to the dimension or dimensions to be sensed.

Abstract: A system for recording and/or reading signals on/from information carriers (4) accommodated in cassettes (2) composed of cassettes (2-3A) of a first type and cassettes (2-3B) of a second type, which two types of cassettes have substantially identical dimensions and shapes apart from local identifying distinctive features (22-3A, 26-3A; 22-3B, 26-3B) of a first type and of a second type respectively. Drive apparatus constructed to cooperate with a cassette of the system when inserted in a correct orientation. Drive apparatus of the first type, is constructed for cooperation with cassettes (2-3A) of the first type but not for cooperation with cassettes (2-3B) of the second type, and drive apparatus of a second type, is constructed for cooperation with cassettes (2 3B) of the second type but not for cooperation with cassettes (2 3A) of the first type.