Google's codebase -- the programming instructions that run every one of its services from Gmail to Slides -- span a whopping 2 billion lines of code that stretch across 1 billion files and require 86 terabytes of storage, according to Google engineering manager Rachel Potvin. She recently disclosed those figures at the @Scale engineering conference. She also noted that this massive collection of data is mirrored and continually updated in ten data centers peppered around the globe. "Not only is the size of the repository increasing," Potvin explained during her lecture, "but the rate of change is also increasing. This is an exponential curve."
There's a solid reason behind keeping all that code in a single, monolithic base: it makes updating everything much easier. That's because the codebase is available to 95 percent of Google's engineers and changing any line of code in one service updates that same line of code in any other service that shares it. Some 15 million lines of code in 250,000 thousand of those files are modified weekly. "When you start a new project," Potvin told WIRED, "you have a wealth of libraries already available to you. Almost everything has already been done."