The new Apple 27" iMacs announced last month ships with a monitor with the insanely high resolution of 5120-by-2880. When you sit down in front of one of these you are looking at 5120 pixels wide * 2880 pixels high * 4 bytes per pixel = 56Mb of data.
To put that in perspective, the first computer I bought with my own money was a Commodore Amiga 500 in 1990. For the time it was an advanced machine with a special chip (the blitter) that could write almost 4 megabytes per secondaccording to the Amiga Hardware Manual if you set things up juuuuust right and the wind was behind it.
That means that an Amiga working flat out could just manage to clear a retina display in slightly over 14 seconds, whereas the iMac can draw a whole frame every 60th of a second. Computing has come a long way in 24 years.
(adjusted for inflation, the iMac is probably cheaper as well)