tape records

[utzoo!decvax!ucbvax!unix-wizards]

>From decvax!jmb at 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.