The VAX is running

Richard legalize at
Sat Apr 4 13:45:58 CDT 2009

In article <ec771527c0a0c99d33c9adc43d6bb32d at>,
    Daniel Seagraves <dseagrav at>  writes:

> A block is a sequence of tape frames. Those can be 7 or 8 bits wide 
> depending on your hardware. Blocks have length, and can vary in length 
> from block to block. You can have a small descriptor block between long 
> data blocks on the tape, where the small block describes what the next 
> large block contains, and so on. You can tell if a block is a 
> descriptor by its length, or looking for a magic number at the start of 
> the block, or whatever.

OK, this seems to indicate that there is a well defined mapping
between tape frames and bytes.  Since a block is a sequence of tape
frames, that implies that blocks are well mapped to a sequence of
bytes.  I guess I'm still missing something that magtape solves that a
stream of bytes doesn't solve.

My understanding is that the hardware tape interface just delivers a
sequence of tape frames without any additional interpretation and that
its the driver/OS/whatever that interprets the tape frames into some
larger structure.

> Tapes also have file-marks.

How is that represented?
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