By "The Science of Discworld" Hex was capable of "once and future computing": increasing its abilities simply by deducing that the required processing power would exist eventually. Presumably this requires a high expenditure of magic, as it has not been mentioned again; at the time, there was a massive "excess" of magic available due to a near catastrophic overload of the university's experimental thaumic reactor. This virtual memory appeared as translucent silver towers superimposed onto the real Hex. Hex was sufficiently intelligent by this time not to tell the wizards what it was doing, in case it worried them.