Help, please, my brother in 2008-2009 was engaged in mining and then reinstalled windows, now he is trying to restore the files. But the question is, was at that time bitcoin wallet in the file wallet.dat?
I think it must have been 2009 as Bitcoin was only released in January of that year! If your brother started mining at any point in 2009, he got in *very* early. I really hope he is successful in recovering the bitcoins.
To answer your question; yes, the private keys to the Bitcoin wallet were contained in the wallet.dat file, same as today.
Very thank you Steven Hay!