The Google Web Server - custom-built server software used only by Google - now runs nearly 13 per cent of all active web sites, according to the latest survey data from the web-server-tracking UK research outfit Netcraft.

Netcraft data has the Google Web Server (GWS) running nearly 11 million active sites - i.e., sites with recently updated content. This total includes not only sites run solely by Google, but also sites the company operates on behalf of third parties via services like Blogger, Google Docs, and Google App Engine.

Apache is still the most prevalent web server, with nearly 44m active sites, and Microsoft servers are second with nearly 14m. But the Google Web Server tops all others and trails Microsoft by a mere 3m sites - despite being unavailable for use outside what Mountain View has called "the Google Network," a worldwide proprietary infrastructure that amounts to a private internet.

Apache and Microsoft servers are available to anyone.

Google does not discuss GWS. In the past, some reports have indicated that it's based on Apache. But in a 2007 web post, über Googler Matt Cutts indicated otherwise. "That's not correct," he wrote. "I believe GWS is a custom web server, not a modified version of Apache."

Google did not respond to our request for comment on the Google Web Server. And on previous occasions, it has given other news outlets a mere one-line description. "The Google Web server is a custom-built server that runs on Linux."

When Netcraft looks at all websites - active or not - the Google Web Server accounts for 7 per cent, or 14.5m. Apache handles around 111m (54 per cent), Microsoft nearly 49m (24 per cent).

Google's private internet - which spans nearly 40 data centers across the globe - is built atop countless custom-built and proprietary tools, including a top-secret distributed file system dubbed GFS; the distributed number-crunching platform known as MapReduce; and a new platform known as Spanner that's designed to automatically move and replicate loads between the company's mega data centers when traffic and hardware issues arise.

Google also builds its own data centers and its own servers, with design help from Intel and, according to one source speaking with The Reg, a breed of Intel chip guaranteed to withstand higher temperatures. Reports even indicate that Mountain View builds its own routers.

What's more, Google has purchased its own dark fiber to move data between its data centers, and the company is building an underwater comms cable to move data across the Pacific.

According to the latest report from Arbor Networks, Google now accounts for 6 per cent of all internet traffic. ®