Can I transfer files from an older Mac to a newer Mac mini using target disk mode?

The Target Disk is the Mac that you want to treat as a disk.

In your case that would be the 2009 Mini. Actually, for two reasons: 1) that's where the files are that you want to transfer to your M1 Mini and 2) no version of macOS on the 2009 Mini would be capable of recognizing the APFS formatted disk(s) on your M1 Mini if you put the M1 Mini into Target Disk Mode.

That said, I completely agree with @den.thed's recommendation to use an external drive to transfer the files. This is actually so much simpler than using TDM. Format it as MacOS Extended (Journaled), then connect it to your 2009 Mini and copy the files you want to transfer. Eject it from the 2009 Mini, then connect it to your M1 Mini and copy the files you want.

The old Mac mini uses FireWire 400 and the new Mac mini uses Thunderbolt 3/4 for TDM.

In order to do TDM between those Mac mini's, you would need three adapters

1) a Thunderbolt 3/4 to Thunderbolt 2 adapter

2) a Thunderbolt 2 to FireWire adapter

3) a FireWire 800 to 400 adapter

and a lot of luck.

Instead of purchasing $120 dollars worth of adapters that might work, your best bet is get and use an external drive. Plus then you could continue to use the external drive for backups, instead of having a bunch of useless one time used adapters.

You will need two adapters and a cable:

• Apple Thunderbolt 3 to Thunderbolt 2 adapter
• Apple Thunderbolt 2 to FireWire adapter (unfortunately these are getting hard to find but you can probably find them via some online retailers)
• Firewire 800 cable like this one

Connect the Macs to each other with those adapters & cable, then boot the 2009 Mac into Target Disk Mode.

Note: Depending on the amount of data you want to transfer it would be easier & cheaper just to use a flash drive. Or for larger volumes of data use an external USB drive. Or you could set up File Sharing and use your home network to transfer the files (it would be at least as fast and possibly faster than using TDM and the adapters and you wouldn't need the adapters.)

tcarder wrote:

My ignorance is showing. I would like the late 2009 Mac mini to appear on the desktop of the Mac mini 2020. How can I make that happen?

With either a collection of not-cheap I/O adapters that will probably be used just once and that may well cost as much as a decent-capacity USB 3.x hard disk drive, or you can make that happen with a decent hard disk drive that you can re-use for the transfer and can then re-use for backups on the new Mac. This assuming the old Mac mini still works, and can run Time Machine.

Here’s a 5 TB HDD USB-A for ~USD$110:

https://www.amazon.com/Seagate-Portable-External-Hard-Drive/dp/B07VS8QCXC

Or you can manually transfer what you want over, after starting over with a fresh install, as was mentioned. I might consider that fresh start, or might use Setup Assistant to migrate just files and documents from the old Mac, and not apps. This if the Mac is filled with older and less-used or unused apps.

You'd need a FW400 cable+FW400+FW800 adapter, or FW400<-> FW800 cable+Apple ThunderBolt2 to Firewire800 adapter+Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter!

If the 2009 iMac is still running it'd be way cheaper to get a USB2 external to copy & move files.

Personally, and without contradicting “the” preferred manner, i am a fan of taking the opportunity for a real cleanup.

that means longer, but yes: everything (data only) on an external drive. 

then reinstall apps from scratch (latest compatible versions).  It may allow you to realize yoo no longer need to occupy real estate on your internal drive for an app you have not used for years and no plans either to use it!

then, same reality when moving back your data: your 76 copies of same picture may not be necessary. Other data may live happily on an external drive or in a dropbox or elsewhere.  Data from your wife’s profile (and that profile itself) may no longer be necessary now that she has it on her own mac (or if you replaced her 🤣)…. 

More importantly, you are limiting risks to bring back corrupted data or programs to the new mac 🤷🏽‍♂️

Yeah, that means a few hours +++ but it may be a better investment than later having to cope with lack of space, an unidentified issue with a culprit you brought back….

Theoretically that would work, I used a Thunderbolt/FW adaptor and a FW800 to FW400 dongle for quite a few years because I had $$$ invested in FW external drives. I assume the added TB adapter wouldn’t cause any issues. But as you say, unless the OP has some of the components already it would be an expensive 1 off.

dwb wrote:

I used a Thunderbolt/FW adaptor and a FW800 to FW400 dongle for quite a few years because I had $$$ invested in FW external drives. I assume the added TB adapter wouldn’t cause any issues.

I initially did the same with my old FW drives. But my Thunderbolt-connected LG Ultrafine monitor had random few second blackouts which I suspect were related to those clumsy two adapter dongles. So I got OWC dual drive SATA-USB dock for the old bare HDDs and new SSDs and it has worked great.

I didn’t have any issues but it was a bit awkward and made cable routing a bit of a hassle. I eventually ditched the FW enclosures for TB enclosures when the prices became more reasonable.

Ah, thanks missed that it had FW800, so my instructions should have said...

Apple ThunderBolt2 to Firewire800 adapter+Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter!