And are they both running Mac OS X Mavericks version 10.9.5??
Personally, for an average user, an external USB drive of at least the same capacity as your Macs should be adequate. One for each Mac would probably be a more convenient usage, and formatted to "Mac OS Extended (Journaled)".
You can use the included
Time Machine System Prefs app, and/or, many, including myself, would suggest using Carbon Copy Cloner (CCC) to create a full bootable clone.
As for your Mac OS updates, check your Software Update and/or your App Store, then check the Updates tab and maybe even your Purchases tab for an option to download any the newer Mac OS that might be shown or listed. You may have even downloaded it previously and it's sitting on your Mac, normally in the Applications folder from where it will normally be run to do any update.
PS: If so, make a copy of the installer and move it somewhere safe before you run it. The one in your Applications folder will be deleted automatically after it has been installed and your Mac OS has been updated.
PS: Your comment on your "
expertise is in high speed race cars" certainly piqued my interest as I used to be quite involved with some of them many years ago, but times and technology have changed drastically.
- Patrick
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