Sony has revealed that the PlayStation 4 Pro has an additional gigabyte of memory compared to the existing unit. This bonus is not directly for use in games, but to help the console with application switching; currently that process is handled by the existing 8GB GDDR5 RAM included with the PS4, but now it can be offloaded to the extra memory unit.
This, according to Mark Cerny, does free up an additional 512MB RAM for software to take advantage of. "Most of that is used for the various buffers needed when rendering high-resolution or higher-quality graphics, and the game assets… Stay the same, they just look a heck of a lot better on the new console."
Nice to know.