This animated GIF comes from Ken Shirriff's blog. Shirriff used a vintage IBM mainframe computer to compute the cryptographic "hash" functions that are the basis of bitcoin mining:
The IBM 1401 can compute a double SHA-256 hash in 80 seconds. It requires about 3000 Watts of power, roughly the same as an oven or clothes dryer. A basic IBM 1401 system sold for $125,600, which is about a million dollars in 2015 dollars. On the other hand, today you can spend $50 and get a USB stick miner with a custom ASIC integrated circuit. This USB miner performs 3.6 billion hashes per second and uses about 4 watts.
Shirriff's also produced a Mandelbrot image on the mainframe. His photos of the hand-wired guts of the IBM 1401 are fascinating.