Wallpaper or Screensaver: What Still Means
One is a file you look at; the other is a program that runs once nobody is looking.
The screensaver began as a repair for a hardware problem. On a CRT tube, a bright menu bar parked in the same place for months could scorch a faint ghost into the phosphor, so the machine was told to keep something moving after a few idle minutes. Flat panels do not hold an image that way, and the flying toasters quietly gave their slot back to a simpler instruction: after fifteen minutes, go dark.
These are not the same kind of object. A wallpaper is a file — one image on disk, drawn behind the icons for as long as the desktop is visible. A screensaver is a program with a timer, and the moment it starts is the moment you have left the chair. Turning the panel off costs less power than any animation, which is why most systems now default to sleep and treat the moving picture as decoration.
There are still two honest reasons to keep one. OLED pixels age unevenly, so something that drifts across the frame spreads the wear, and a screensaver that demands a password on wake was the original privacy latch — a job the lock screen has since taken over. What remains is a division of labour worth noticing: the screensaver performs for an empty room, while the wallpaper is the picture you actually see, three seconds at a time, in the gaps between one window and the next.
