That I don’t know, but I believe the blocks were generated and placed in the public domain in the beginning. Also, initially, the difficulty level was easy so even CPUs were used to mine. A well know story is how back then, it took thousands of bitcoins to buy a single pizza.
I’m probably wrong about the Pentium 7. It probably can do twice what I said above, so it may only take it 23 years to find a bitcoin. ;)