As reported in the LA Times, Morgan Stanley analyst Mark Edelstone claims Google now has at least 200,000 servers in its cluster. Mark also says that Google will be switching to servers with AMD Opteron processors for most new purchases.
Looking at the AMD product line, I see that AMD has a new line of dual core (two processor), low power (55W) processors, the HE chips. Looks like a nice blend of reduced power and high performance there.
For more on why that's important to Google, see Googler Luiz Andre Barroso's discussion of heat, power, and performance issues in the Google cluster in his ACM paper, "The Price of Performance", and my discussion of that paper in my earlier post, "Power, performance, and Google".
[Found on Findory]
Update: See also my other post, "100k+ new servers per quarter at Google?"
Update: Three months later, John Markoff and Saul Hansell at the New York Times report that "the best guess is that Google now has more than 450,000 servers spread over at least 25 locations around the world." [via Don Dodge]
Update: Six months later, a paper on Google Bigtable mentions that Google is using machines with two dual-core Opteron 2 GHz chips. Sounds like Google is using the new AMD 2 GHz dual core Opteron HE.