1000 Machines Find the Results for a Google Query

How many servers process a Google query and serve the top search results? Google Fellow Jeff Dean says that more than a thousand machines are necessary to obtain the search results in less than 200 milliseconds.

"Their performance gains are also impressive, now serving pages in under 200ms. Jeff credited the vast majority of that to their switch to holding indexes completely in memory a few years back. While that now means that a thousand machines need to handle each query rather than just a couple dozen, Jeff said it is worth it to make searchers see search results nearly instantaneously."