What external storage options are available for the Apple Silicon iMac? Should I buy USB-C or Thunderbolt external storage?

Ports are a bit confusing for the Apple Silicon iMac models.

Entry-level models from each year have "two ports" -- "Thunderbolt / USB 4" -- whereas higher-end models have "four ports", but until the iMac "M4" 10 CPU/10 GPU/4 Ports 24" (2024) was introduced, which has a more straightforward four "Thunderbolt 4" ports, two ports are "Thunderbolt / USB 4" and the other two are slower USB 3.

All of these ports use a USB-C shaped connector, so it can be a bit confusing to decide which storage to purchase, as well.

When storage is listed as "USB-C" this generally means it is USB 3 speed with a USB-C shaped connector. Thunderbolt 3, Thunderbolt 4, and USB 4 also all use a USB-C shaped connector, but these standards are significantly faster than USB 3.

Specifically, applicable ports for each Apple Silicon iMac model are:

24" iMac	Subfamily	Model	USB 3	USB 4
"M1" 8 CPU/7 GPU	M1 2021	A2439	None	2
"M1" 8 CPU/8 GPU	M1 2021	A2438	2	2
"M3" 8 CPU/8 GPU	M3 2023	A2874	None	2
"M3" 8 CPU/10 GPU	M3 2023	A2873	2	2
"M4" 8 CPU/8 GPU	M4 2024	A3247	None	2
"M4" 10 CPU/10 GPU	M4 2024	A3137	None	4

Accordingly, for any Apple Silicon iMac, you should buy external storage labeled as Thunderbolt 3, Thunderbolt 4, or USB 4 -- advertised as "up to 40 Gb/s" -- to maximize its performance.

Simple, High-Performance iMac External Storage

Photo Credit: OWC Express 1M2

Although other drives also will work, a great option is the straightforward, high-performance OWC Express 1M2 from site sponsor Other World Computing.

The OWC Express 1M2 contains an upgradable NVMe M.2 SSD and can be configured with up to 8 TB of storage.

High-Capacity, High-Performance iMac External Storage

If you want the option to inexpensively expand your external storage over time, you might prefer the 4-slot M.2 NVMe SSD-based OWC Express 4M2.

Photo Credit: OWC Express 4M2

Compared to the OWC Express 1M2, the OWC Express 4M2 is more complicated, but also supports as many as four industry-standard internal M.2 NVMe SSDs for as much as 32 TB of storage.

Because the OWC Express 4M2 itself is easy to upgrade, it is straightforward to start with one SSD and add more as needed. Accordingly, this solution can be much neater and easier to manage than having a pile of external drives scattered around your iMac.

To determine whether or not the OWC Express 4M2 could meet your needs, you might find this video that explains how to install storage useful, too:

Whether you prefer straightforward, but still upgradable, individual storage or an expandable option for large capacity, the OWC Express 1M2 and OWC Express 4M2 are ideal options to consider.