RAM usage may go up to 400, 500 or even more Megabytes easily. This increases to a lot more when you don't open the image directly in Photos but go to the visual listing of all available photos instead. If you use both tools to display the same image, Photos uses about three times as much RAM as Windows Photo Viewer. Why you would want to use Windows Photo Viewer and not Photos? Easy: Photos uses a multiple of the memory that Windows Photo Viewer required to display images. Microsoft ships Windows Photo Viewer will clean installations of Windows as well but it is hidden and cannot be reactivated this easily.
Windows Photo Viewer is available as an option if the device was upgraded from an earlier version of Windows, e.g. Windows Photo Viewer is still available on Windows 10 devices but the program's accessibility depends on whether Windows 10 was clean-installed. Windows 10 users who worked on devices running previous versions of Windows or are still working on those devices may have used Windows Photo Viewer in the past to view images on these devices.
