How to connect an iMac 27inch from mid-2010 to a MacBook Pro 2023 ?

I will normally agree with our colleagues @dialabrain and @den.thed that use of your old iMac as a monitor is not possible. But I've learned recently that beyond the typical target display mode feature - currently quite dead - a couple old iMacs included native support for video input via DisplayPort sources. You're in luck because your 27" mid-2010 iMac is one of these.

iMac (27-inch, Mid 2010) - Technical Specifications - Apple Support

❝ Graphics and video support

• [...]
• Mini DisplayPort output with support for DVI, VGA, and dual-link DVI (adapters sold separately); 27-inch models also support input from external DisplayPort sources (adapters sold separately)

As for your MacBook Pro, the specs indicate support for DisplayPort output via USB-C.

MacBook Pro (16-inch, Nov 2023) - Tech Specs - Apple Support

❝ Display Support

[...]

M3 Max

Simultaneously supports full native resolution on the built-in display at 1 billion colors and:

• Up to four external displays: Up to three external displays with 6K resolution at 60Hz over Thunderbolt and one external display with up to 4K resolution at 144Hz over HDMI
• Up to three external displays: Up to two external displays with 6K resolution at 60Hz over Thunderbolt and one external display with up to 8K resolution at 60Hz or one external display with 4K resolution at 240Hz over HDMI

Thunderbolt 4 digital video output

• Support for native DisplayPort output over USB‑C ❞

For your case, I recommend that you use a high quality USB-C to DisplayPort cable from a Thunderbolt port of the MBP to the DP input of the iMac to get the job done. Maybe even a certified Thunderbolt 3 to DisplayPort cable, though that might be overkill. If you search Amazon or google you'll find the proper cable.

If you review the very restrictive hardware and OS requirements for the now-deprecated Target Display Mode:

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

you will see that no Mac made after 2019 supports Target Display Mode.

Even if it did, the cost of Thunderbolt cabling and adapters could cover most of the cost ofa decent external monitor.

Apple started the deprecation of TDM in late 2014 and threw the last shovel of dirt in its face in early 2020.

After-market "solutions" are laggy and often expensive.

No that will not work using a cabled video connection.

You can use a network connection like macOS screen sharing or duet displays, but that is not as robust as using an after-market display with the MacBook Pro. Use an external display with your MacBook Pro - Apple Support

That MacBook Pro has USB-C ports that support DisplayPort Alt Mode.

If Apple had not added restrictions saying that no recent Mac supports using any iMac as a Target Display, a USB-C to Mini DisplayPort adapter cable would be the obvious way to connect the two. Based on Technical Specifications alone, one would expect the arrangement to work. The whole point of display standards like DisplayPort is to ensure interoperability.

Given the statements in the Target Display Mode Support article, your MBP is too new to use the iMac as a Target Display. I do not believe that Apple has explained the discrepancy.

With most of the 2011 to mid 2014 iMacs that support Target Display Mode using Thunderbolt input, the feature is not mentioned anywhere in Technical Specifications, so might be seen as more “subject to change.”

zebumax wrote:

Thanks a lot to all.

I suppose that buying a specific screen will be the best solution.

That is certainly the easiest, but there might less costly solutions depending on your needs. There are a few 5K monitors on the market, each with their own limitations and they typically run $700-$1600. Before buying you might like to explore some other ideas.

In the last little while I purchased a Mac Mini M4 Pro thinking that initially I could use one of my 2 old iMacs. One is an old mid 2010 with the newest OS it can have, and the other is a 2015 with OS Monterey (again the newest it can support). I have been able to use both of these iMacs with my Mac mini M4 pro with varying amounts of performance and features. So here is a couple of thoughts for you:

1) A simple way to get signal from the source to the IMac is to use an HDMI cable with an HDMI to USB video capture card to plug into one of the USB ports on the iMac. You can get these for around $25. You could then use a simple video app like Quick Time to feed the signal from the USB port to the screen. Note that most inexpensive capture cards only support up to HD (i.e. 1k). This is a shame since the mid 2010 Retina display is a 2k type display (which is why it looks so good). Note that a normal USB to HDMI cable adapter will not work since they are designed to send the video signal from the USB end (on the computer) to the HDMI end (on the monitor).

2) The 2010 iMac's mini display port *CAN* be used as a video input but only if it is properly fed with a mini display port cable and signal. Note that although the MDP has the same physical characteristics as a Thunderbolt 2 port, they are not interchangeable. Thunderbolt 2 cables can be plugged into a MDP, but it will never work. Note that there are 4k HDMI to MDP converters out there that might work for a direct connection, but I didn't get around to trying this myself as I decided instead to use my 2015 iMac with its 5k Retina display.

[Edited by Moderator]

zebumax wrote:

Is it possible and how ?

It's not possible.

Screen sharing or bust — not cabling. The word "should" does not represent empirical testing that proves it is possible.

Re: “I tryed to connect both wit a Usb-C adaptor (iMac side) to the MacBook with a cable USB-C to HDMI (MacBook)... but with no result.”

That would definitely fail, even if Apple had not added restrictions on Target Display Mode. USB-C to HDMI adapters are generally unidirectional, and only work if the USB-C end is plugged into a USB-C host or dock port that supports DisplayPort Alt Mode. I don’t know what you were plugging in, where, on the iMac side, but it likely was wrong, too.

The Mini DisplayPort on the 27” 2008 and 2010 iMacs supports Target Display Mode using regular DisplayPort (not Thunderbolt) input.

Logically. a USB-C to Mini DisplayPort adapter cable should work, but given the restrictions that Apple retroactively placed on the video source, it might not. The kludge that the OP describes would have had no real chance of working with or without those restrictions.

VikingOSX wrote:

[...] The word "should" does not represent empirical testing that proves it is possible.

No disagreement from me on this.

I'm just relaying info that is available within Apple's own spec sheets and confirmed by at least a couple previous users. I was surprised to learn this myself, but the feature is there in a very limited number of 27" iMacs. I don't know exactly which releases support it, but the mid-2010 does.

lkrupp wrote:

So have you personally seen this setup work? Otherwise I think this unhelpful to a user asking for advice.

Could, maybe, might possibly...

I have communicated directly with at least two users here in the community who have successfully used this setup. As I've posted, I was surprised to learn this because conventional wisdom is that old iMacs cannot be used as monitors, particularly with target display mode.

But there is a situation where TDM is not required to be use, and that would be in the case of an iMac that natively supports a DP input signal, as the 27" mid-2010 iMac is spec'ed.

The typical response to the use of target display mode with old iMacs is still "No. Can't be done."

The author's OP didn't specifically mention TDM, but was simply asked if that particular iMac be used as a monitor. Apple did indeed spec it to leverage DP input with appropriate adapters.

So, is this unhelpful? I don't think so. Is it potentially confusing or conflicting? Sure, I'll give you that. But you can thank Apple for it.

Jeff Wiseman wrote:

There are a few 5K monitors on the market, each with their own limitations and they typically run $700-$1600.

Those 27" 5120x2880 pixel monitors would be an upgrade from the 27" 2560x1440 pixel screen that the OP has now. They're not the only option. You can purchase decent, if basic, 27" 2560x1440 (2.5K) and 3840x2160 (4K) monitors with IPS panels and 100% or near-100% coverage of sRGB for $300-$400.

1) A simple way to get signal from the source to the IMac is to use an HDMI cable with an HDMI to USB video capture card to plug into one of the USB ports on the iMac.

A HDMI capture device with 720p or 1080p resolution, feeding its output into a USB 2.0 port? No thank you.

the mid 2010 Retina display is a 2k type display (which is why it looks so good)

It is not a Retina display. It is a high-quality display with standard pixel density (PPI). The 27" 5K Retina iMac displays and 27" 5K Apple Studio Displays are Retina displays. Their screens have 2x the PPI of the 27" 2010 iMac's screen. (4x as many pixels per square inch for drawing letter shapes and photo content in finer detail.)

Note that although the MDP has the same physical characteristics as a Thunderbolt 2 port, they are not interchangeable. Thunderbolt 2 cables can be plugged into a MDP, but it will never work.

Thunderbolt 1 and 2 host ports on old Macs can act either as Thunderbolt ports or Mini DisplayPorts, depending on what's attached to them. You could use a 27" 2010 iMac that needs Mini DisplayPort input as a Target Display for a 27" 2012 iMac that had Thunderbolt 1 ports, and you could use a high-quality Thunderbolt 1/2 cable to make the connection.

The Apple Thunderbolt 3-to-2 adapter does not know how to pull this same trick. It translates Thunderbolt only.

zebumax wrote:

I suppose that buying a specific screen will be the best solution.

That would be the best idea.

Re: “But there is a situation where TDM is not required to be use, and that would be in the case of an iMac that natively supports a DP input signal, as the 27" mid-2010 iMac is spec'ed.”

That specification implicitly refers to Target Display Mode. There is no DP input that you can use without being in TDM. The issue is not that you need to be in TDM, but that TDM is now more restrictive than DisplayPort compatibility would imply.