Calculate the amount of memory required for a 320x240 256 color display: 320*240 = 76.8KB. An Arduino only has 2KB of RAM, so an external controller has to do b

Calculate the amount of memory required for a 320x240 256 color display: 320*240 = 76.8KB. An Arduino only has 2KB of RAM, so an external controller has to do basically all of the drawing opereations. This controller has its own SRAM framebuffer. Once you get larger than 640x480, it becomes impractical to have the framebuffer in SRAM. DRAM is the obvious choice, but increases system cost and complexity sharply and so you first see it on "application processors", e.g. Cortex-A7 and up. Also, DRAM PCB routing is very complex, and the connection from the display controller / system-on-chip to display is also critical.