We disassembled the 2k rom back then. There are routines for drawing text, character by character, pixel by pixel. The code is terribly not-optimized but fits in 2k including the character set. Hardware just has a single frame buffer at a fixed address. 4 pixels per byte, 32 bytes per line, and that includes over scan and horizontal blanking so 112 to 114 pixels wide 3 scan lines tall. Doubling the pixel clock, devoting more ram to it, and using the empty rom socket would have made it quite a machine for back then.