Daisy Chain old iMac to new iMac?

NewsView wrote:

I have a 2009 Intel Core 2 Duo iMac (iMac10,1) with CS6 that I don't want to lose access to; however, I need to upgrade from my ancient iMac to obtain a current OS/web browser. If I buy a newer iMac (*MHJY3LL/A) can I set the older iMac to Target Disk Mode and *boot* into it using the newer iMac as my display (toggle between the old and new iMacs as needed)?

No. If you're talking about Target Disk Mode, that's a non-starter for at least two reasons:

1. If either Mac has Big Sur or later installed, you can't use USB Target Disk Mode. You have to use Thunderbolt Target Disk Mode – and 2009 iMacs don't have Thunderbolt.
2. Even if you could make the connection, that wouldn't give the new Mac the ability to run CS6 (or to boot using the version of macOS installed on the 2009 iMac).

Transfer files between two Mac computers using target disk mode - Apple Support

I read in an Apple support document that 2019 and newer iMacs don't support Target Display Mode. Is that relevant to my particular situation or would it be considered a master/slave setup between the new iMac and old iMac?

Yes. Neither Mac could be a display for the other.

• The new iMac can't be a TDM display for the other because it is too new.
• The old Mac might be a 21.5" Late 2009 iMac (that doesn't support TDM) or a 27" Late 2009 iMac (that does). But even if it was a 27" Late 2009 iMac that supports Mini DisplayPort TDM, the new Mac would be "too new" and thus would not be able to take advantage of the old Mac's TDM features.

Use your iMac as a display with target display mode - Apple Support

Basically I just want to use the new iMac as a display for accessing the old iMac applications, and for all the other tasks not related to legacy applications to boot into the new iMac/OS.

Unfortunately, it won't work that way – at least not with Target Disk Mode or Target Display Mode.

For this, would I also require a Firewire to Thunderbolt adapter?

You would only need that adapter if you have FireWire peripherals you want to save.

If you have a MiniDV or Digital8 camcorder with a (FireWire / iLink / IEEE 1394) interface for transferring digital video, then you might need a chain of adapters: Apple TB3-to-TB2 => Apple TB-to-FW800 => FW800 to 400 cable.

If you're hooking up old external drives, some of them may already have dual FireWire / USB interfaces (simply switch to the USB interface if you transfer the drives to the new computer), and in other cases, you could think about transferring the drive mechanisms to new USB-A (USB 3) or USB-C (USB 3) enclosures.

What would be the correct steps to get this type of setup working, assuming it can be made to work?

You'll probably have to look at other options – like:

Set up some sort of software-based screen sharing (if you can find anything that works with the 2009 iMac).

Get a big desk and put the new and old systems side by side, without trying to use one as a display for the other.

Get a big desk and a monitor that has two video inputs and connect both Macs to that monitor. Use the monitor's controls to switch the screen between acting as a display for the new Mac, and a second display for the old iMac.

Maybe enable File Sharing on one Mac, and have it serve up a folder on its drive to be mounted as a network drive on the other machine.

Upgrade to the current version of Photoshop (although that would mean paying subscription / rental fees for one of Adobe's Photography Plans).

Switch to an editor other than Photoshop (such as Affinity Photo V2, or GIMP) if you can't stand the subscription (rental) model, and need a powerful editor, but don't have a specific requirement for Photoshop.

Your old macOS install not going to boot and run a recent iMac.

I'm making some assumptions here, including the central role of CS6, and that the Adobe Creative Cloud subscription is not interesting to you.

You can keep running CS6 on the old Mac certainly, or can replace CS6 on the new Mac with any of the fine alternatives to Adobe products, including Acorn, Affinity, and Pixelmator Pro.

If you really want to work at what is probably a somewhat more supportable variant of what you are envisioning (mostly to keep CS6, if this follows a common pattern of postings around here), you can acquire a used Intel Mac, and can probably then install OS X 10.11 as a guest in a virtual machine, and run CS6 there. With an Apple silicon Mac, the analogous approach gets more involved, as you'll need not only a virtual machine but also an emulator—UTM, maybe—and that all then gets slower, and potentially less stable.

Don't get too focused on an effort to (badly) replace an external hard disk with an ancient and tiny and slow hard disk in that old iMac, too. An iMac is a terrible and terribly inefficient external disk mounting enclosure, and a hard disk from 2009 is just not worth preserving. Your goal and your focus here should (probably) be centrally about CS6, or about an Adobe CS6 replacement.

NewsView wrote:

I have a 2009 Intel Core 2 Duo iMac (iMac10,1) with CS6 that I don't want to lose access to; however, I need to upgrade from my ancient iMac to obtain a current OS/web browser.

With respect to the Web browser, you can't upgrade beyond the High Sierra version of Safari. (High Sierra being the latest version of macOS that will run on that Mac.) The only way to get to a newer version of Safari is to get a new machine.

However, the version of Firefox that runs on High Sierra is still receiving updates. Until you get the new Mac, you might want to consider using it for some of your Web browsing.

https://www.mozilla.org/en-US/firefox/new/