http://blogs.zdnet.com/storage/?p=638

From the article:

"A two-and-a-half year study of DRAM on 10s of thousands Google servers found DIMM error rates are hundreds to thousands of times higher than thought — a mean of 3,751 correctable errors per DIMM per year.

This is the world’s first large-scale study of RAM errors in the field. It looked at multiple vendors, DRAM densities and DRAM types including DDR1, DDR2 and FB-DIMM
...."

via /.