3TB Drive as Primary - Can I use MBR with 2 partitions?

I recently bought a 3TB replacement drive for a PC of mine that DOES NOT have a UEFI BIOS. I converted it on my primary PC to GPT being ignorant of the fact that legacy BIOS do not support booting from a GPT drive (or maybe it's a Windows thing), so I re-formatted in with diskpart in the recovery console inside the Windows 7 installation disk and it split the drive in two. A 2TB partition and a 746GB partition, which is fine.

The problem is, when I try to format the 746GB of unallocated space in disk management in Windows 7, all it does is give me an error and deny me. Having the 2TB partition and the 746GB partition is fine. I just need both to be usable.

All input it is appreciated.
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  1. Best answer
    MBR can't address drives further than the 2-and-a-bit TB mark. Unfortunately, Windows won't legacy boot off a GPT drive (for no particular reason; plenty of Linux distros can).

    Your best bet is either to just use the 2.x TB, or to get a smaller HDD (or SSD) and put windows on that, with data on the GPT-partitioned 3TB drive.
  2. Thanks for the quick reply. I expected as much from what I had read but didn't know if there was a way around it. Seeing as there's no way to update the PC's BIOS to UEFI I guess I'm out of luck on the extra 750GB.

    May just cannibalize the drive later on in a UEFI PC anyway. Thanks.
  3. If you use it as a secondary drive, you can use the whole 3TB. It's just the boot drive that can't be >2TB.
  4. Well, the PC I installed it in was a repair job on the primary. I wasn't too educated about that particular aspect of storage in Windows. The PC was one of those no-tower monitor PCs with a touchscreen so it only had room for a single drive. Thankfully my friend was very gracious and didn't mind that he could only use 2TB of the space.

    I also knew I could use it as a secondary but it's good to list that as others searching for this thread may find that information useful. If it had space for a spare drive, I would have just given him a spare of mine and put that one as the secondary but I didn't have that option. The issue is resolved though.

    In conclusion for anyone referencing this forum in the future, GPT as a primary drive in a PC without a UEFI BIOS is a big no-no.
  5. Yeah, GPT as a primary drive doesn't work without UEFI if you're running Windows.

    However, the only real reasons to use GPT are >2TB drives and to run Windows in UEFI. You can change the drives pretty easily.
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