Some articles on datapaks, datapak:

Psion Organiser - Organiser I
... The machine could host two of these so-called DATAPAKs (or simply PAKs), to which it could write data but which needed to be removed from the machine and erased by being exposed to ultraviolet light ... Software supplied on DATAPAK included a crude programming language called POPL, in which end-users could write their own programs ... Software DATAPAKs titled Science, Maths and Finance contained the POPL programming language editor, interpreter and runtime and extended the built-in calculator by adding named functions ...