The 10 Biggest Tech Companies You've Never Heard Of

With all the talk about Dell going private so it can revamp itself without Wall Street on its back, we got curious.

Who are the biggest private enterprise companies? Better yet, who are the biggest private companies under the radar?

So we looked around. We examined at our own Digital 100 list of the most valuable private tech companies in the world. We scanned through the Forbes list of America's Largest Private Companies. We looked at the Inc. 500 and the Silicon Valley Business Journal's lists, too. (All used estimated revenue for 2011, the latest full-year data available.)