As seen on Slashdot, a Microsoft tech blog outlines their hosting environment for microsoft.com. One of the interesting items that came up was that until a year or so ago, they were using NLB (Network Load Balancing), the no-frills Windows server Layer 4 load balancing that is included with the OS. Since 2006 however, they’ve been using Citrix NetScaler.
Update: 12/19/2007
As a few have pointed out, this link is now dead. It looks like Microsoft didn’t quite like having that much info divulged publicly. Here is the original slashdot post.
To summarize, they now use Citrix NetScaler as the load balancer for a multi-Gigabit traffic for Microsoft.com, although in the past they’ve used the NLB (Network Load Balancing) part of Windows Server.
That link seems to be broken.