IBM 5110 User Manual page 84

Now, assume you add data to the data file at a later time (an ADD
operation). The new data starts at the first 512-byte boundary after
the last record in the data file. The tape storage between the last data
record and the additional data records is unavailable for use. Once the
new data records are written to tape, the data file might look like this:
Data File
512-Byte Boundaries (tape storage is
jdivided into 512-byte segments)
,
,
I I I I I
I.
Data Records----..
~~~.--Additional
Data
o_- . ..
..,...'7'"""T'"-.r-T'""lr-r-J-I
1
~ginning
of unavailat. Last Data Record / . n u L d
the Data File Tape Storage Tape Storage
As you add more data to the file, it is possible for more tape storage
to become unavailable. You can compress the data in the data file (use
the unavailable storage) by first reading all the data records from the
file and then writing the data records back to the file, starting at the
beginning of the data file (an OUT operation).
Tape Concepts 79