MNIST is a toy problem. It shouldn't take you more than a few days or even hours to completely understand it. Do yourself a favor and get a GPU because soon you

MNIST is a toy problem. It shouldn't take you more than a few days or even hours to completely understand it. Do yourself a favor and get a GPU because soon you will want to try bigger networks on real world images. 1060, 1070, or 1080Ti are all good choices, depending on your budget and ambitions.