For a little less distant comparison, you could buy a Sun E10k in 1997. It was roughly two full racks in size with 64 total Sparc CPUS delivering ~50GFlops.
So 18 of those needed, 36 full racks of space, 1152 CPUs to get to 900GFlops. Each 10k is roughly 39"W x 50"D x 70"H, so about ~244 square feet of floor space for 18 of them, not including space needed around it. Including the space around it, it would be a typical 1BR apartment full of compute.
Also, I assume the M1 does significantly better than 900 GFlops if you don't run it through the browser.
A single E10k fully populated needs 11,041 watts, not including the needed air conditioning. So 198kW for 18 of them. I don't know how to convert Btus/hr into power, but each E10k needs 37,165 Btus/hr of A/C.
The Macbook Air M1 would be something lower than 30W, since that's what the power supply is rated for.
37165 BTU/h is roughly a quite convenient 10 BTU/s. 1 W is 1 J/s, and 1 BTU is about 1000 J. So the AC would need about 10 kW, or 180 kW for all of them.
All in all the computers in the example thus come out at north of 400 kW for total power use. Yikes!
That's a power reduction by a factor of more than 13,000 in less than two decades!
Put differently: If your electrical power comes from burning coal, the 1997 alternative to the computing power of a single M1 would emit about 8000 kg of CO₂ per day. The equivalent of driving 80,000 km with a very modern gasoline car. The mind boggles!
“since that's what the power supply is rated for.“
Theoretically, that machine could use more power at full speed. That would mean you couldn’t charge it fast enough to keep it running at top speed forever, but that might not even be noticeable because you hit a heat limit earlier.
In practice, I guess the power usage is lower, as https://support.apple.com/kb/SP825?locale=en_US says it has a 49.9‑watt‑hour lithium‑polymer battery. At 30W, you would run out of that in less than 2 hours (but again, at full speed, you probably hit a heat limit earlier)
So 18 of those needed, 36 full racks of space, 1152 CPUs to get to 900GFlops. Each 10k is roughly 39"W x 50"D x 70"H, so about ~244 square feet of floor space for 18 of them, not including space needed around it. Including the space around it, it would be a typical 1BR apartment full of compute.
Also, I assume the M1 does significantly better than 900 GFlops if you don't run it through the browser.