Memory with millennia of data retention, if you vist Egypt you will find data in the form of hieroglphys written a few millennia ago and is still readable today, albeit with a little dificulty and only a few bits. That highlights a second problem with the search for the millennia memory (MM), as well as the data the means of reading it must survive the same length of time. Hieroglphys point to part of the way to go, i.e store in stable structure and read optically, (For the ancients that was chisel in, eyeball optical out). So for the tera byte MM, store the data in a form of structure that does not rely on a metastable state, that is a crystal rather than a glass. All of this would suggest a three dimensional block of material employing some form of internal structural change as the means of storing the data with optical read/write access. It certainly looks as though the group at U of Southampton reported above are moving in the right direction.