Fun fact about the TI-99/4A: It was actually fast, sporting a 16-bit CPU in an 8-bit era. The BASIC interpreter was slow because it, like many TI-99/4A programs, was written in a sort of interpreted bytecode that could live in video RAM/ROM. The CPU itself had access to only 256 bytes of system RAM; all other RAM in the system was video RAM that had to be accessed through the video chip. The slowness of the video RAM access, coupled with the fact that the interpreter for your BASIC ran on interpreted bytecode instead of native CPU instructions, meant that your BASIC programs would crawl, but give that 16-bit chip a chance to open up and it can do some amazing things. The game Parsec has a smooth scrolling playfield, which the TMS9918A wasn't able to achieve on its own. The CPU is shifting the scenery graphics "by hand" as part of the main game loop.