How much disk space does OS X El Capitan take up? I need a pretty good, accurate figure here, or how to find it myself. I'm getting an external SSD soon, and I'm thinking about installing OS X on it for times when I need a faster system than what my built in HDD can offer, and need to choose either a 1TB model, or 500GB model. Bear in mind that I'll be using the SSD to store HD video on too, so it won't be just OS X on there. I may also try and be sneaky and find a way to install Windows on there, but my method in mind seems risky, and dodgy, and will probably cause me multiple issues.