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Call for information on virtual tape formats 354


Tim Shoppa

Well, there are tape systems that can only write 512 byte blocks, most of the QIC formats. Some were designed around floppy disk controllers.

IBM S-360 style disks put the label on the 3rd block, so that IPL records can go on blocks 0 and 1. I would expect, then, that IPLable tapes can't be SL or AL.

There are stories of people writing tapes with one (very long) record on S-370 using data chaining. That is, more than on CCW per tape block.

Call for information on virtual tape formats 356
I think that you'll find that in many cases tape drives will read the short...

IBM mainframes will consider an error in reading a short block as noise, but I believe if it reads without error it is fine.

Read errors were much more of a problem on 800 BPI (NRZI coded) tapes than on 1600 BPI (PE) or 6250 (GCR). NRZI depends on there being at least one transition per character, so must be odd parity. It is, then, very sensitive to head azimuth. All tracks are clocked together. PE and GCR clock each track separately, and so are much less sensitive to head azimuth.

New or old, reading 800 BPI tapes on a different machine was never easy.

Call for information on virtual tape formats 355
Joe Morris I recall a card-resident dump program for the S-360 model 44 that could dump all of...

You could always write a virtual tape file on a real tape.

-- glen


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Call for information on virtual tape formats 355

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Call for information on virtual tape formats 353