You may have heard the term 4K a lot lately (at least when I wrote this, beginning of 2014), 4k is quite a trendy subject. To understand what is is let’s first understand what “HD” means.

Careful, this is an ultra-simplification. I’m only going to talk about the most common resolutions. There is different categories of HD.
The term HD is applicable to any resolution starting from 1280x720px or 720p for 720 horizontal lines. Some may also call this resolution SD for standard definition

The term full HD applies to the 1920x1080px screens. Most TVs uses this resolution and more and more high end phones (Galaxy SIV, HTC one, Sony Xperia Z, Nexus5)

4K starts at 3840×2160 pixels. It was also call Quad HD and can be referred to as UHD for Ultra HD. Simply put, you can put 4 1080p in a 4K screen in term of number of pixels.

Another resolution of 4K is 4096×2160. It’s slightly larger and used for projectors and professional cameras.

What happens if I plug a 4K display to my computer

Current OS do not scale 4K, it means that if you plug a 4K display to a Chromebook or a macbook, it will use the highest DPI asset, in this case the 200% or @2x ones, and display them at normal ratio, making everything look good but tiny.
Hypothetical example: If you plug a 12″ 4K screen to a computer with a 12″ hi-res screen (2x), everything will appear twice as small.

– 4k is 4 times Full HD.
– If current OS handles 4K but do not scale it, meaning no 4K specific assets yet.
– No phone or tablet uses 4K as of today.