I always wanted to know more about the customized Google servers. The cool part is that they have implemented a distributed UPS (each server has his own battery and charge controller):
Instead of having a centralized UPS, Google integrated a battery into every server with a charge controller and test circuit. The battery is sealed lead-acid. Basically, it is a car battery. The goal is to keep the server running for “about a minute” until the generator turns on or the A/C power source is switched. The power supply ONLY provides 12VDC (notice the yellow 12V wires coming out of the power supply), and the power only goes to the motherboard. The motherboard then directly supplies power to the disks (at 5VDC) and no other voltage conversions occur (with the exception of 1.2-1.8V for the processor). As such, the AC feed of either 208VAC or 230VAC flow directly to the server with no UPS in the middle. The battery backup directly supplies 12VDC during power outages, so no more inverters. The power supply is about 92% efficient according to Google. The “distributed UPS” solution is estimated by Google to be “99.9%” efficient since there’s no power distribution losses by operating directly at the DC voltage of the server.