A proposed unit of data equal to 10^27 bytes. A brontobyte is 1000^9 bytes or 1000 yottabytes. "Bronto-" is not an official prefix and the term brontobyte is generally attributed to the IBM Dictionary of Computing. One brontobyte would be enough data to store a three-dimensional map of the Earth with one byte for each voxel of a one-centimetre grid. See prefix.