You will get most of your answers from a document such as this one, or by Googling. Using only one byte of two has little to do with drive size, and much to do with not getting bitten by the unused upper byte.

'Enterprise' often equates with 'bespoke' or 'made-to-order', which manufacturers often don't list with their standard offerings. There may be difficulties with such drives in ordinary systems, eg when the drives have been configured for Unix environments. Only use will reveal this state of affairs to you, but you can sometimes recover from it with drive utilities other than Apple's.

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