You can do it on a poorer graphics card, but that's only if it has enough GPU RAM, and only if its supports a relatively recent compute version.

You _can_ run it on a CPU, and that can work fine for very simple models (like the Tensorflow demos with MNIST) but anything much larger and things really start to take forever. Like, you'll be waiting for months.

I'm giving serious thought to buying or building a rig for these courses. What's "enough GPU RAM"?

A GTX 1060 with 6 GB of RAM is a good intro card. You can find them for < $350.

The AWS P2 instances recommended for the course ($0.90/hour) have half a K80, which has access to 12 GB of VRAM. The list price for that card is $5000.

The GTX 1080 Ti has almost as much VRAM as half a K80, 11GB, and can be found for around $700.

I'm finding Acer rigs with GTX 1070, 8GB RAM. I'll probably get one of those, thanks.

You can. Tensorflow has a CPU implementation. But, it's not a little longer, it's incredibly longer.

Like 5h on an upper-class GPU vs 50 days on the fastest CPU.