Google is 40 times as big as Microsoft Windows.

Google’s Rachel Potvin came pretty close to an answer Monday at an engineering conference in Silicon Valley. She estimates that the software needed to run all of Google’s Internet services—from Google Search to Gmail to Google Maps—spans some 2 billion lines of code. By comparison, Microsoft’s Windows operating system—one of the most complex software tools ever built for a single computer, a project under development since the 1980s—is likely in the realm of 50 million lines.

25,000 engineers have contributed to Google's code base.

Basically, Google has built its own “version control system” for juggling all this code. The system is called Piper, and it runs across the vast online infrastructure Google has built to run all its online services. According to Potvin, the system spans 10 different Google data centers.

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Piper spans about 85 terabytes of data (aka 85,000 gigabytes), and Google’s 25,000 engineers make about 45,000 commits (changes) to the repository each day. That’s some serious activity. While the Linux open source operating spans 15 million lines of code across 40,000 software files, Google engineers modify 15 million lines of code across 250,000 files each week.

By comparison, the main Facebook app spans upwards of 20 million lines of code, and the company treats the whole thing as a single project.