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Aucbvax.5078 fa.unix-wizards utzoo!decvax!ucbvax!unix-wizards Tue Nov 10 05:47:31 1981 tape records >From decvax!jmb@Berkeley Tue Nov 10 05:11:35 1981 To answer Lauren inre why a block must be between 18 and 2048 bytes:

That convention is now part of ANSI X3.22. To be "industry standard" (read that IBM compatible) any block of 'data' must be at least 18 bytes long. This makes sense in that some standard is needed so the hardware can detect "crap in the gap". (I wish there was some more elegant way to put that but I know no other description for this error condition)

The maximum of 2048 was established in the dark ages (pre PDP11 anyway) by a large computer vendor in the N. Y. I assume that this was for purposes of pre-allocation of tape buffers in a non-interactive, ie batch, mode of operation.

To make a short story long, on UNIX I would suggest you maintain the minimum above 18 bytes for hardware reasons. (see above - I don't want to use that repugnant phrase again). The maximum record length is one of convention. If you don't intend to pass the tape to one of those other, inferior, operating systems you can let UNIX conventions by your quide.

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