I just found several boxes of "Verbatim DC 30 Data Cassette" tapes. I've never seen these before. Does anyone knwo what they're for? In their boxes, they measure 4 3/8" x 2 7/8" x 5/8". The look like an over-sized audio cassette tape. They're driven by the tape hubs and the case does not have a metalbase plate like that found on most data cassettes. There is a note on the back of the tape saying "Do not to record on this side. Side B has a 1600 FCI Pre-recorded clock track for tape speed control". Joe