Can I run a Mac Mini M4 from an external SSD at the same normal speed?

Yes you can run the mini off an external.

I ran my base model M2 mini from a cheap (£60) 1 TB SSD USB 3.0 from October 2023 to November 2024.

The speed of the USB 3.0 drive is only one fifth (20%) that of the mini's drive but Geekbench tests gave identical results.

So what about real-world situations? Apart from the usual websurfing etc. I edit 1080p and 4K video with Final Cut Pro and Davinci Resolve Studio.

Subjectively the editing was just as crisp and on rendering and exporting it was a tad slower by up to 4% which is really negligible.

The only time you notice the slower speed is when copying massive files (50 GB plus) when of course it will take 5 times longer but that is something I rarely do.

Last month I decided to get the utmost performance and bought a 1 TB NVMe in a Thunderbolt enclosure for £130.

This drive is faster than the internal and there is no reduction in performance but I'm not sure whether it was worth it as the old USB 3.0 SSD was fine.

The bottom line is that the speed of the drive has very little effect compared to the speed of the processor.

Try it and see for yourself. I think you will be pleasantly surprised.

I'm not sure why you'd want to run multiple copies of the same version of macOS, but yes, you can install macOS on an external SSD and boot from it. See:

Install macOS on an external storage device and use it as a startup disk - Apple Support

Regards.

I am not exactly sure what you mean by running multiple copies of the macOS?

At present I have got my "old" SSD running Sonoma and my new NVMe running Sequoia but I can only boot into one at a time.

It takes less than a minute to change the boot drive.

We can't really give you a blanket answer without specifics. It depends on the SSD and how it's connected to the Mac. If it's a high-performance SSD in a quality case connected by Thunderbolt 4 (or TB5 if it's a Mac mini M4 Pro) would probably be at least close to the performance of the internal drive, but that's a big if.

Note that an M4 Mac mini will not run any version of macOS earlier than macOS 15 Sequoia. So unless you plan to run Linux - if there's a distro that will work on an M4 Mac - then unless you need larger storage, there's really not much point in going with an external. Even then it would probably be more effective to just use the external for data storage and not try to boot from it.

Regards.

If you are getting the base model the M4 is a no-brainer as it has 16 GB RAM.

Having said that, my M2 has only 8 GB but it's more than enough for my needs as I am not a heavy user.

The main reason I booted from an external was to protect the tiny 256 GB SSD from excessive wear but when I found that even a cheap USB SSD was virtually as fast I was elated!

What is wrong with you and the kids each having your own account on the same drive?

You would all have privacy and there would be no need to keep rebooting a different drive when someone else wanted to use the computer.