Are modes 8,9,10 things like 320*200 in 16 colours? Remember the CGA monitor can display 16 colours (there are 4 TTL-level digital input lines). The original CGA card didn't have enough memory (or the right logic) to do anything more than 2 colours at 320*200, although the monitor would have been capable of it. The PC-jr did have enough memory for this.