Nowadays, a terabyte (or several) is standard for personal use, and petabytes are what we talk about when we have to make a point about how much data is stored by Facebook and Google. And soon those terms won’t seem so big, either, as we move on to exabytes.
The problem is that after exabytes, we have zettabytes, and then yottabytes, and then — nothing. Zetta and yotta (and their submultiple counterparts, zepto and yocto) are the most extreme numerical prefixes we have. They were made official in 1991 at the 19th General Conference of Weights and Measures. Evidently they didn’t foresee the need to describe anything with a greater multiple than yotta, or 1,000,000,000,000,000,000,000,000.
Indeed, yotta-anything sounds like it should be enough. The diameter of the observable universe would be approximately just 880 yottameters, points out Jessica Leber at MIT’s Technology Review — meaning if there were a bigger prefix than yotta, the entire universe would fit inside one of them.