(Edit 3/16/2012: I am surprised that this post is picked up by a lot of media outlets. Given the strong interest, I want to emphasize what is measured and what is derived. The # of server racks in EC2 is what I am directly observing. By assuming 64 physical servers in a rack, I can derive the rough server count. But remember this is an *assumption*. Check the comments below that some think that AW
![Amazon data center size](https://cdn-ak-scissors.b.st-hatena.com/image/square/31d5762ac2856c119eca9dda203f56ccde8116ed/height=288;version=1;width=512/https%3A%2F%2Fhuanliu.wordpress.com%2Fwp-content%2Fuploads%2F2012%2F03%2Fec2-us-east-data-center-size-growth.png)