 Regardless of how much free space might remain on the disk in total, it was not available to extend the data file.Standards of error handling at the time were primitive and in any case programs squeezed into the limited memory of the BBC Micro could rarely afford to waste space attempting to handle errors gracefully.Instead, the user would find themselves dumped back at the command prompt with the "Can't extend" message and all the data which had yet to be appended to the file would be lost.