So... just how big are tomestones?

[Anonymoose]

They are suppose to work as a pen drive?

Exactly. Kind of. The information is read / written by computer equivalents, but (going by the French name memoquartz) the actual data storage medium is just regular old quartz crystal. It's possible to synthesize quartz and it can hold data engraved on it for millions of years.

And where is the allagan PC substitute? I dont believe there are abailiable allagan PC somewhere to decipher it.

There were some on Azys Lla and some in the coils, but I doubt many were salvaged by us. Garlemald (or at least House Darnus) seemed aware of how to decipher the data. But for all we know it might be as easy as having a cipher of the encoding language, a nice microscope, and some free time. Even Y'mhitra is able to work on deciphering them, though it's clearly a time-consuming process for her. But, again, who knows what the Sons of Saint Coinach have for resources, tech-wise.