27" Imac Late 2013 - External HDD or SSD Compatibility

External USB3 drives are not specific to any computer and can be formatted

for macOS, Windows, Linux or any other OS that supports USB mass storage

devices.

However, many manufacturers will bundle software on the drives that may

or may not be OS specific, hence "compatibility" statements. As a major

rule, never, ever install any software that you may be prompted to install

when plugging in a new drive as it is never needed and will only create

problems.

I have a Late-2013 27 inch iMac here and I exclusively use Crucial MX500 SSD externally. These are in Vantec USB3.1 Gen 2 enclosures which come with both USB3 A cable which plugs into USB3 port on the iMac, and spare USB-C cables for future proofing. I also have a $33USD Inland USB3.1 Gen 2 hub connected to the iMac because I was flat out tired of reaching behind it for connections.

For the moment, I have Catalina 10.15.1 installed on one of these external SSD and it boots and runs almost as well as if it were booted internally.

I've never had good luck with Lacie drives, however many of experienced users on these forums and myself prefer the OWC Mercury Elite Pro series of drives due to their extreme reliability, reasonable prices, the ease of changing the HD when it dies and how many capacity variations they offer, from 1-14TB. You can find them by clicking https://eshop.macsales.com/shop/owc-mercury-elite-pro/usb-3.1

Like many old hands here, I'm not a fan of "pre-built" external drives. I prefer to build my own which gives me total control over the components. I prefer OWC (macsales.com) and IcyDock drive enclosures. Depending on how I'm going to use the drive I'll purchase Western Digital Blue, (normal use), Black (for high capacity & speed) or Gold (for backups). For SSDs I prefer Crucial Tech and OWC - basically whichever has the best price at the time. I've also purchased a few Western Digital PCIe SSDs. Today's enclosures are truly plug and play so it takes no real experience to put them together.