RAM to support a computer screen display
One reason GUIs were initially slow to be adopted was the cost of the hardware needed to support them. How much video RAM is needed to support a 25 line X 80 row character monochrome text screen? How much for a 1024 X 768 pixel 24-bit color bitmap? What was the cost of this RAM at 1980 prices ($5/KB)? How much is it now?