PMODE 4
The Dragon32 home computer hit the UK market in 1982 and it was immediately apparent that it was a near exact copy of the Tandy Color Computer, aka the CoCo.
The highest resolution, PMODE 4, is 256x192 in a black-and-white or black-and-green palette. Up to 8 graphics pages can be reserved, via PCLEAR 8. PMODE 4,1 addresses pages 1 to 4, whilst PMODE 4,5 addresses pages 5 to 8. SCREEN 1,X displays whichever 4 pages are currently being addressed and X = 0 or 1 simply selects the palette.
On bootup, the graphics pages aren't nicely initialised to a bunch of zeros. Instead it's mostly alternating FF 00 hex bytes, with some random-looking bytes interspersed at regular intervals. It makes for a very intriguing pattern. Black pixels correspond to the binary digit 0, green to 1.
The image shows all 8 graphics pages in one contiguous bitmap. The top half, down to but not including any of the horizontal glitchy rectangle, constitutes the first 4 pages, and is what you would see in PMODE 4,1. The bottom half, which starts with the horizontal glitchy rectangle, would be visible in PMODE 4,5.
I won't bore you with a guided tour of the image, showing you where it contains regularity amongst chaos, and irregularity amongst order. I will let you stare at it and discover these secrets for yourself!