Jews and other folks that keep Torah do not kindle a flame on the Shabbat. For those who are very strict about keeping God's commandments (basically orthodox Jews), they avoid anything that would create a spark. This spark is like a very tiny, short lived flame. Any time physical electronic contacts join together (like when turning on a light switch), the argument is that there's a very small spark that occurs. The same would happen with the electric contacts in a motor, such as the motor inside CPU fans, desktop power supplies, and platter hard drives. By running on this physical hardware, they're avoiding breaking the Sabbath as much as possible.
source: I'm a gentile Christian that tries to keep the Torah. So I'm more familiar with Jewish laws than the average person, but don't quote me too much.