The Xerox Alto doesn't use a framebuffer, it only stores bitmaps for each window and the microcode looks at them to work out what to put on each scanline of the

The Xerox Alto doesn't use a framebuffer, it only stores bitmaps for each window and the microcode looks at them to work out what to put on each scanline of the display. In comparison, the original Mac "wastes" RAM by always reserving enough to represent the whole screen but this does give it more flexibility in what you draw to it.