The c64's default video mode was a 40x24 grid of 8x8 monospaced text characters. The video chip was designed around this: each scanline it would look at the cha

The c64's default video mode was a 40x24 grid of 8x8 monospaced text characters. The video chip was designed around this: each scanline it would look at the characters occupying the current row, then use that plus how many times it'd displayed that row as an index into the 1k of character ROM to pull out the appropriate byte, and display its individual bits as pixels. You could also tell the video chip to look somewhere in RAM for these character definitions. Maybe just to replace the standard font with something cooler; maybe some of your font would contain little 8x8 building blocks you could use to make bigger images. Most games would build their backgrounds this way - you'd only have so much variation available, but you also only had to move about 900 bytes around to scroll the screen, rather than 8k. Which sounds like nothing to a modern machine but was a serious difference for a 1mhz computer. The bitmap mode jiggled with this a little, and ignored the 'look at the characters on this row' part in favor of just stepping through an 8k chunk of RAM over the course of the display. (Well, the multicolor bitmap mode looked at the characters in the row as well, but used them for color data rather than an index to the character map.) If you want to know about this in more detail then try firing up a c64 emulator and going through the 'graphics' chapter of the c64 Programmer's Reference Guide: http://www.commodore.ca/manuals/c64_programmers_reference/c64-programmers_reference_guide-03-programming_graphics.pdf http://www.commodore.ca/manuals/c64_programmers_reference/c6... I'm not sure the acronym "API" even existed at this point in time. I sure never heard it when I was fooling around with 6502 assembly. tl;dr: severely limited hardware, programmed right on the bare metal. API? What's that?