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Jack Ghiselli e-mailed Oct 27, 2019
IBM magnetic tape labels
(written onto the tape)
I donít remember the 1401 writing Tape Labels in a different parity or density from the main data.
Our 1401 production tapes had internal Header Labels and Trailer Labels. Tape labels were 80 byes (of course, Mr. Hollerith). You wrote a Tape Mark (electronic marker for end of data) after the Header and before the Data. Another Tape Mark after the Data and before the Trailer. Another Tape Mark after the Trailer. When you were writing a large file on to a blank tape and hit the End-of-Tape reflective marker, you closed off Reel 1, and began Reel 2 of the file. The reflective spot does not stop data writing, so the last half of the last data block, a Tape Mark, a Trailer Label, and another Tape Mark were all written after the reflective marker. Pessimists like me always left lots of extra tape after the End-of-Tape reflective marker. We did have a few special tapes with no internal Tape Header Labels.
IBM published a format for Tape Labels. It had a file identifier and a reel number for multi-reel files. It had a place for creation date and time, but that had to wait until the 360. Lots of other unused fields. IBM (bless their hearts) even made provision for multiple Headers and Trailers on a given tape with additional user-defined information.
We wrote our own 1401 IOCS to handle Tape Labels since we couldnít find any of you clever IBM-trained dudes.
If a computer operator did you dirty, a nasty comeback was to stick an extra End-of-Tape reflective spot on a scratch tape an inch or so after the Start-of-Tape. This could cause IOCS and the operator to go nuts. Or, so Iíve heard tell.