It may seem weird, but the Tandy 1000 copied the graphics modes from the IBM PCjr, not the EGA standard. That included a 320x200 16 color mode, as well as 640x200 four color mode that the original CGA couldn't do (because it lacked memory). The IBM PCjr also included a sound synthesis chip (don't recall which one off the top of my head) that may also have been included in the Tandy 1000 (don't know, had the PCjr, not the Tandy).