Those are just assumptions. I got it from an inside source that a high res texture pack would be around 150GB but that Carmack was toying with the idea of an uncompressed version. So I guess that's our best shot and we don't exactly know how that would work or what it will use.
Inside source... lol. Sorry, but that's not credible.
And it remains a fact: uncompressed would be in the terabyte range, according to previous statements. As for how it would work - it's simple arithmetic. You either uncompress the data in CPU/GPU, or transfer the data over SATA bus.