Disc System User Guide (1982).

The above method will only work consistently if you start with a blank,
formatted disc. If you want to create a random access file larger than 64
sectors on a disc with other files already on it, there is another method.
First save the file with the name you want and with the number of bytes
required. Use the address parameters of the *SAVE command to specify the
number of bytes, e.g:
*SAVE "DATA" 00000 08000
will create a file of 128 sectors (32K) called DATA. You can then open the
file later in your program. The file will contain miscellaneous data which you
can overwrite with the information you actually want. This second method
causes the filing system to search the disc for a free space large enough to
hold the file. Existing files will be skipped over if they would otherwise
overlap with the new file
Note 2
Up to 5 files may be open at any one time. This is because the space reserved
for each file in the computer's memory to hold the information about extent,
pointer etc. is limited. In certain versions of the disc filing system, the
commands *LOAD, *SAVE, *EXEC, *SPOOL, *BUILD, *LIST and
*DUMP each use the space occupied by the information relating to one open
file while they are active.
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