I had a raid before with 2 1T Hitachi Deskstar, yes I do know what a raid is, I can only afford 1 4T now so that is why I said "eventually". My bios is so old I have to use a HGST disk manager to format GPT. the docs say it will render it unable to be used as boot or raid--probably because the OS/bios will not support UIEF so I expect that is why it will not boot or raid but could be used as storage only. My Win 7 64 will not format GPT-that I can find.
Hence the question which I think I have answered is that without a supportive bios I'm stuck and need to get a couple of 2tb drives if I want to raid drives now.