As a Windows specialist, I am baffled by the behavior of the Apple App Store. First of all, I can't understand the reason why it won't allow a download of an OS X app to a machine that isn't compatible with that particular version. Is Apple trying to restrict the number of downloads? Or are they trying to protect the more obtuse user from downloading something that he can't use? Anyway, today I using an iMac that is running High Sierra 13.10.4. All I want to do is download the High Sierra Install App so I can create a bootable USB using DiskMaker_X_7 and install it on another iMac. When I go to the App Store, I am not able to find the "Download" button. Where is it? I do see an "Open" button, but it downloads a little 508 MB file. What I really need is the full app, whose size is somewhere around 5 GB. What am I doing wrong?