-snip-
I was wondering, who or what determines when new coins are mined, and how many?
Everything is in the software's code.
There's no "
who", just the
miners who compete for the winning blocks.
"
when" is completely 'average', there's an ever-adjusting 'difficulty' that ensures that blocks can be mined in an
average of 10minutes.
Each block's reward is
currently 6.25BTC (
+fees) which was 50BTC when Bitcoin was just released because it halves in every 210,000 blocks.
Pretty much everything covered in this 'the Bitcoin Wiki' article:
en.bitcoin.it/wiki/Mining