How to add another monitor to a Retina Mac computer

Question

How to add another monitor to a Retina Mac computer

I have a Retina Mac computer [yes an old model], how can I add another montior

iMac 21.5″, macOS 12.7

Posted on Dec 7, 2025 1:07 PM

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Answer 1

Top-ranking reply

Servant of Cats

Level 7

34,181 points

Dec 7, 2025 2:14 PM in response to Help_Me_Support

iMac (Retina 4K, 21.5-inch, Late 2015) - Technical Specification - Apple Support

That computer has old-style Thunderbolt 2 ports, with Mini DisplayPort connectors, that can double as Mini DisplayPorts.

It can drive a single external display. If that display has a DisplayPort or Mini DisplayPort input, that would allow the use of a simple cable. Otherwise, you will need an adapter or adapter cable.

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Answer 2

rkaufmann87

Level 10

148,440 points

Dec 7, 2025 1:13 PM in response to Help_Me_Support

We need the model year and display size of the iMac. You can find this information by clicking the Apple symbol in the upper left of the display and then click About this Mac. Once you have that we can tell you the cable you will need, then connect and follow the steps in Connect a display to your Mac - Apple Support

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Answer 3

Dec 7, 2025 1:43 PM in response to rkaufmann87

Mac (Retina 4K, 21.5-inch, Late 2015)

C0******G78

Hardware Overview:

Model Name: iMac

Model Identifier: iMac16,2

Processor Name: Quad-Core Intel Core i5

Processor Speed: 3.1 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 4 MB

Memory: 8 GB

System Firmware Version: 489.0.0.0.0

OS Loader Version: 540.120.3~37

SMC Version (system): 2.32f21

Serial Number (system): C0******G78

Hardware UUID: 1B55FF12-A5E6-5250-BF52-8A90D345E767

Provisioning UDID: 1B55FF12-A5E6-5250-BF52-8A90D345E767

[Edited by Moderator]

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Answer 4

Dec 7, 2025 3:49 PM in response to Help_Me_Support

You cannot update that Mac past macOS 12.* (Monterey), no matter what hardware upgrades you make to it.

The RAM is sealed inside. You could pay a repair shop a lot of money to open the Mac and replace the existing 8 GB with 16 GB (the maximum), but I’m guessing the 8 GB you have now is enough. If you do add more RAM, I would advise buying it only from Other World Computing. But I don’t see the value in adding RAM given the cost, the likely benefit, and the age of the machine.

Getting an external USB SSD and making that your startup drive might help with speed - keeping in mind that it won’t do anything to help you run current applications or current versions of macOS.

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Answer 5

rkaufmann87

Level 10

148,440 points

Dec 7, 2025 5:32 PM in response to Help_Me_Support

"I'm focused on finding the most cost-effective fix possible. Is there a way to reasonably boost its speed without breaking the bank?"

You have several options, buy a refurbished Mac from Apple. You can use Apple's 12 month same as cash option if you would like. If you purchase a new Mac from Apple you can also use their 12 month same as cash option. Another option is to buy a used Mac from one of Apple's trusted reseller sites such as MacSales.com, however NEVER EVER buy a used Mac from:

Ebay
Amazon
Craigslist
Nextdoor
Local PC Shop
Friend, Neighbor, relative

Why..these Macs are not prepared correctly and are not refurbished with quality components.

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Answer 6

Dec 7, 2025 2:41 PM in response to Help_Me_Support

Thank you. As someone living on a fixed retirement income, replacing my perfectly good Mac simply isn't an option. While this old workhorse is reliable and meets my basic needs, its performance has slowed down considerably, which wasn't the case when it was new.

I'm focused on finding the most cost-effective fix possible. Is there a way to reasonably boost its speed without breaking the bank? I'm wondering if adding a bit more RAM or making another affordable upgrade is the best move, or if I should even risk updating the operating system (I think it's called iOS, but I mean the Mac OS) given how much slower new software can run on old machines.

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