The file follows TI's standard certificate format used on many caculator models.
See TIGCC's documentation for more information (more particularly cread and cfindfield).
The indentation corresponds to subfields.) As for TI-Nspire.cer, the file is organized as a certificate.
(Format of the following section: Field ID (hex) - size (dec) - @TI-Nspire: offset of the current version (hex) - @TI-Nspire CAS: offset): comment.
Sending a to a TI-Nspire CAS is possible and vice-versa, but at the end of the reception a message will be displayed by the Computer Link Software indicating that the file is corrupted, and the OS won't be installed.
A .tno/is a PK-Zip file with a custom ASCII header describing the OS update file.