The operating system should be responsible for managing resources like RAM, and applications should be responsible for using the right resources. Caching video

The operating system should be responsible for managing resources like RAM, and applications should be responsible for using the right resources. Caching video is absolutely a RAM thing, since it's expected to go away once the video is done. Caching downloads is a separate matter, since it's expected to stay once finished. A good litmus test here is what you expect to happen if the machine reboots. For video, I think it's reasonable to lose all video cache, but I think downloads should be resumable. If it shouldn't be there on a reboot, use RAM. If it should, use disk. There are certainly exceptions, but I think the general rule of thumb is useful.