To dual boot from an SSD with a 2 TB HD for data, must I use UEFI?

Question

I currently have a 120 GB SSD with Windows 7 and a 2 TB harddrive for data. I wanted to install Ubuntu alongside win7 on the SSD but as I am using UEFI I ran into lots of problems and gave up after a day wasted.

My question is, with my setup, must I use UEFI considering I have a 2 TB HD? Or, considering I am booting from the small 120 GB drive, can I not use it?

Answer 1

No. You do not need to use UEFI.

You can use it if you want, but you only need if you want to be able to boot from a disk larger than 2 TB.

Note that the MBR partition scheme and a regular BIOS will handle drives up to 2 TB just fine. The problems starts with drives larger than 2 TB.

Also, you can use a larger than 2 TB drive from an OS. Once you booted the OS from another source (for instance from a 120 GB SSD) and loaded the right drivers you should be fine. Even with disks larger than 2 TB and/or formatted with other partitioning schemes. (e.g. GPT).

Answer 2

Since Windows is already installed, it's imperative that you install Ubuntu in the same mode (BIOS/CSM/legacy vs. EFI/UEFI) as Windows. If you don't, you'll have to jump through extra hoops when booting one OS vs. the other, or it will be harder to install an appropriate boot loader to change Linux's boot mode.