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I would like to replace my damaged hard drive on my Mac mini late 2014. Could I get a SSD with The OSX pre-installed, is that possible?
As @vladaad stated drives don’t come with the OS installed you need to install it your self. There are a couple of ways to install a fresh OS with very little effort! If you have a good internet connection you can install the OS via Internet recovery just by connecting your system to either a WiFi or Ethernet connection. If you have access to a second system you can setup your Mac Mini in Target Disk Mode and using a Thunderbolt cable between the two systems you can use the other Mac OS installer to install the OS onto your Mini. Another way is to get a USB thumb drive and set it up on the other Mac or before you remove your current drive set it up as an OS installer. So how do I do all of these different ways? Here you go! Internet Recovery - Restart your system and press Command (⌘) and R keys Target Disk Mode - Restart your Mac Mini system and press T key, then connect your other system to yours via Thunderbolt Cable. Setup a bootable OS installer follow this guide How to create a bootable macOS Mojave installer drive And here’s how to get the best macOS for your system How to upgrade to macOS Mojave (jump down to Step 4 for the direct link) Use this OS for either method. References: How to reinstall macOS from macOS RecoveryMac startup key combinationsUnderstanding the Applications for Target Disk Mode
You can’t buy an SSD with an OS preinstalled. You have to install it yourself from a USB Drive.