Chris> Hi everybody. This is something a computer geezer like me Chris> should know. But I don't. Chris> I've read some things that seem to imply that *some* of the Chris> oldest drive/formatters did NOT write a longitudinal parity Chris> frame at the end of a block. (They did have horizontal parity, Chris> of course.) Chris> If it's true then a drive reading such tapes would not have an Chris> easy way of telling whether frames had been dropped during a Chris> read. Does this ring true to anybody out there? Any Chris> observations welcome. It sounded odd to me, so I did some reading. The IBM 650 (1955) says that it has even longitudinal parity. On the other hand, the Univac Model 1 (1950 or thereabouts) says that it has even horizontal parity but not longitudinal parity. But that's really rather prehistoric and doesn't use regular 1/2 inch mylar tape. Given that even the 650 has it (as do several CDC machines I checked) I'm somewhat doubtful about the rumor. paul