640x480 256 colours on a 286? With only 30 seconds for an image, even though it doesn't have a floating point unit? Sorry for being a doubting Thomas, but that

640x480 256 colours on a 286? With only 30 seconds for an image, even though it doesn't have a floating point unit? Sorry for being a doubting Thomas, but that seems very implausible (having spent my life writing ray tracers).