On macOS memory can be paged to/from disk. On iOS it isn’t and applications must free memory when asked or be terminated
Not sure what you meant by that, you always could `mmap` files into memory on iOS. Back in the 32 bits days there was a ~700 MB limit due to the address space, but there aren't anymore nowadays with 64 bits. If `didReceiveMemoryWarning` is called on your app, then you need to free resident memory but the kernel will take care of dumping file-backed memory pages for you.