Analog Cassettes

Some articles on cassettes, analog cassettes, cassette:

Digital Compact Cassette - Technology - Cassettes and Cases
... DCC Cassettes were almost identical to analog cassettes, except there were no "bulges" where the tape-access holes were located ... The top side of a DCC cassette was flat and there were no access holes for the hubs on the top side (they were not required because auto-reverse was a standard feature ... access holes and locked the hubs while the cassette wasn't in use ...