Also question is, does Apple 4k TV work with 1080p?
If you buy an Apple TV 4K before you get a new 4K/UHD TV, it will detect that the best picture the TV can accept is (likely) HD and auto-select 1080p (or 720p/1080i if the HDTV is older). You won't have to worry about the Apple TV selecting a mode your current (HDMI-based) TV can't handle.
Similarly, does upscaled 4k look better than 1080p? Upscaling means low-resolution content will fill your entire TV screen. UHD upscaling is what makes your 4K TV work like any other. It can take lower-resolution content and display it on the entire 4K screen. Upscaled 1080p content on a 4K screen often looks better than 1080p content on a normal 1080p screen.
Also, will my 4k TV upscale 1080p?
So can good scaling make a 1080p image look good on a 4K TV? Compared to that same content badly upconverted, yes. In CNET's reviews of the better 4K TVs, we've found that 1080p Blu-ray upconverted to the 4K screens looks great, although not appreciably better than 1080p on a 1080p TV.
Does Apple TV improve picture quality?
You get better resolution
This is the most obvious reason. Apple's fourth-generation Apple TV maxed its resolution at 1080p. The Apple TV 4K has nearly four times the resolution. It's a significant upgrade in picture quality over its predecessor.
