user87850: 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?

user60443: 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 <data-dir>. The wallet.dat file was stored in <data-dir>/ on versions prior to v0.16.0 and moved to <data-dir>/wallets in later versions, see files.md. This uses the bitkeys format.
Linux
On linux, the data directory <data-dir> is ~/.bitcoin/wallets/wallet.dat
Windows
On Windows, the data directory <data-dir> is %APPDATA%\Bitcoin\wallet.dat
Mac
On Mac, the data directory <data-dir> 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

87850: <p>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.</p>

<p>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?</p>
 60443: <p>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.</p>

<h2>Bitcoin Core</h2>

<p>The keys are in a file called <code>wallet.dat</code> which was stored in the bitcoin core data directory, which I'll call <code>&lt;data-dir&gt;</code>. The <code>wallet.dat</code> file was stored in <code>&lt;data-dir&gt;/</code> on versions prior to <code>v0.16.0</code> and moved to <code>&lt;data-dir&gt;/wallets</code> in later versions, see <a href="https://github.com/bitcoin/bitcoin/blob/master/doc/files.md" rel="nofollow noreferrer">files.md</a>. This uses the <a href="https://bitcointalk.org/index.php?topic=4448.0" rel="nofollow noreferrer"><code>bitkeys</code> format</a>.</p>

<p><strong>Linux</strong><br>
On linux, the data directory <code>&lt;data-dir&gt;</code> is <code>~/.bitcoin/wallets/wallet.dat</code></p>

<p><strong>Windows</strong><br>
On Windows, the data directory <code>&lt;data-dir&gt;</code> is <code>%APPDATA%\Bitcoin\wallet.dat</code></p>

<p><strong>Mac</strong><br>
On Mac, the data directory <code>&lt;data-dir&gt;</code> is <code>~/Library/Application Support/Bitcoin/</code></p>

<p>Reference: <a href="https://en.bitcoin.it/wiki/Data_directory#Mac" rel="nofollow noreferrer">https://en.bitcoin.it/wiki/Data_directory#Mac</a></p>

<hr>

<p>The next question is "How do I restore the keys?", and there are many answers for that already, example: <a href="https://bitcoin.stackexchange.com/q/10974/60443">Import wallet.dat into a new Bitcoin-Qt client</a></p>
