Western Digital My Cloud Western DigitalBVBZ0040JCH-BESN EX Ultra 4TB 2-Bay 3.0 USB Network Attached Storage (Black) As used for storage capacity, one megabyte (MB) = one million bytes, one gigabyte (GB) = one billion bytes and one terabyte (TB) = one trillion bytes. Total accessible capacity varies depending on operating environment. As used for buffer or cache, one megabyte (MB) = 1,048,576 bytes. As used for transfer rate or interface, megabyte per second (MB/s) = one million bytes per second, megabit per second (Mb/s) = one million bits per second and gigabit per second (Gb/s) = one billion bits per second.