HP T6553 D45 Reference Manual page 97

FUP Commands
Each variable-length, blocked record begins with a word that contains the
length of the record, and the read count equals the value of that length
indicator. You cannot use the TRIM option with VARIN, and this option works
only with tapes written by FUP.
out-option
controls the handling of the output file. out-option is not normally used with
structured disk files.
BLOCKOUT out-block-length
sets the number of bytes in an output block. Specify out-block-length as
an integer in the range 1 through 32,767. This value is the maximum number of
bytes to be written in a single physical operation. If a value greater than 32,767
is specified, FUP issues this error message and then aborts:
ERROR - TAPE DEFINE BLOCKLEN VALUE TOO LARGE
If you specify BLOCKOUT and out-filename is not a tape DEFINE:

If the output-block length is greater than the output-record length, output-
record blocking occurs. The block is filled with out-record-length
records until it contains out-block-length bytes or the last output
record is encountered.

If out-block-length is not a multiple of out-record-length, the last
record in a full block is truncated.

If the write count for a record is less than out-record-length, the
output record is padded in the output block with trailing nulls.

The actual number of bytes written in a physical operation is
out-block-length for all blocks (except the last). If the last block is not
full, the actual number of bytes written is equal to the number of records in
the last block multiplied by out-record-length.
If you specify the BLOCKOUT option and out-filename is a tape DEFINE
with these attributes, you must not specify the BLOCKLEN attribute of the
DEFINE, or the BLOCKLEN attribute must match out-block-length:

LABELS set for labeled tape processing

USE set to OUT (or not specified)
If you do not specify BLOCKLEN, it is set to out-block-length for the life of
the FUP command.
If you omit the BLOCKOUT option, and out-filename is a tape DEFINE with
these attributes, then FUP sets out-block-length to the BLOCKLEN value
of the DEFINE:

LABELS set to labeled tape processing
File Utility Program (FUP) Reference Manual—523323-014
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