How Photos stores images when you migrate your iPhoto library?

Photos stores images when you migrate your iPhoto or Aperture library to Photos app and it saves disk space by sharing images. Once you migrate a iPhoto library to Photos, the Photos app creates a new library structure, but doesn't, in fact, duplicate your images. Instead it "creates links" to the original and preview versions of your images. Finder will report the file size of your Photos library and it will also include all your original photos and previews. It look like your remaining iPhoto library is taking up twice the space on your hard drive, but it is not taking up space. Your images appear only in one location, even if you have more than one photo library on Mac. So you don't need to delete the original iPhoto library, because the migrated library takes little additional space on your Mac.