I know I had Bitcoins back in the Day, but I have all my old computers and have the hard drives, so how do I systematically go back finding which on has my bitcoins?  At the time, I figured it was no big deal, but now finding the correct one, could be worth while.

So my question is, how to I search my hard drives to find the one that contains the bitcoins?   Is there a file I need to search for?
It depends on the version you were running, and the operating system, and when you say you are looking for your bitcoins, what you are really looking for are the private keys.

Bitcoin Core

The keys are in a file called wallet.dat which was stored in the bitcoin core data directory, which I'll call &lt;data-dir&gt;. The wallet.dat file was stored in &lt;data-dir&gt;/ on versions prior to v0.16.0 and moved to &lt;data-dir&gt;/wallets in later versions, see files.md. This uses the bitkeys format.

Linux
On linux, the data directory &lt;data-dir&gt; is ~/.bitcoin/wallets/wallet.dat

Windows
On Windows, the data directory &lt;data-dir&gt; is %APPDATA%\Bitcoin\wallet.dat

Mac
On Mac, the data directory &lt;data-dir&gt; is ~/Library/Application Support/Bitcoin/

Reference: https://en.bitcoin.it/wiki/Data_directory#Mac



The next question is "How do I restore the keys?", and there are many answers for that already, example: Import wallet.dat into a new Bitcoin-Qt client