Fifty-two computers control the systems on the ISS. Some 3.3 million lines of software code on the ground support 1.8 million lines of flight software code. In the International Space Station’s U.S. segment alone, 1.5 million lines of flight software code run on 44 computers communicating via 100 data networks transferring 400,000 signals (e.g. pressure or temperature measurements, valve positions, etc.). Main U.S. control computers have 1.5GB of total main hard drive storage in the U.S. segment compared to modern PCs, which have approximately 500GB hard drives.