3.63 TB ( actual size ) is not the 4 TB size that was advertised, However, the product so far is trouble free and quiet, I have been able to easily ( and super fast ) transfer data from my old 2 TB external to the new 4 TB one. If there is a drawback, it is that the blue light on top of the unit blinks while data is being transferred and it makes falling asleep somewhat harder as the whole room lights up in a blue hue. I placed a piece of paper over the unit to dull the light. I like that It also lays flat on my desk instead of the standing photo which was shown in the advertisement, as this makes it impossible to fall over. I think I will be purchasing a second one along with the Universal driver adapter, so I can transfer data from other drives which have stopped working. If you are not aware of what the Universal Driver Adapter is, check it out on YouTube and I'm sure you'll be getting one as well. It saved me over $1600.00 so far, as some data retrieval services can charge between $800 - $1200 a drive. The Seagate - Expansion 4TB External USB 3.0/2.0 Hard Drive is definitely a good purchase and should have been given 4 and a half stars, ( but there is no way to give a half star ) in my humble opinion.