You’re looking at a sleek, aluminum sliver of a computer on eBay or Facebook Marketplace and wondering if you’ve found a bargain or a trap. It’s the iMac 21.5 inch 2017. It looks almost identical to the ones Apple sold just a few years ago, but looks can be incredibly deceiving in the tech world.
Honestly, this machine occupies a weird spot in Apple's history. It was the last of its kind in several ways. It arrived at a time when Intel was still the king of the hill, and "Apple Silicon" was just a rumor whispered in R&D labs. Today, buying one is a gamble. Some people will tell you it's a perfect budget workstation for a student. Others will say it's a glorified paperweight because of the "Fusion Drive" bottleneck. Both are kinda right, depending on which specific model you’re holding.
The Massive Divide: 1080p vs. 4K Retina
If you are shopping for an iMac 21.5 inch 2017, the very first thing you have to check—literally the most important detail—is the screen resolution. Apple released two very different versions under the same name.
The base model is, frankly, a bit of a relic. It features a 1920x1080 sRGB display. By 2017 standards, this was already looking a little long in the tooth. By today’s standards? It’s grainy. If you’ve spent any time looking at an iPhone or a modern MacBook, your eyes will immediately notice the lack of sharpness. This entry-level version usually shipped with a dual-core Intel Core i3 or i5. It’s a "budget" machine that feels its age every single second you use it.
Then there’s the 4K Retina model. This is a different beast entirely. It boasts a 4096x2304 resolution and supports the P3 wide color gamut. It’s bright. 500 nits, to be exact. Even in 2026, a well-calibrated 4K Retina display from Apple holds up against most mid-range monitors you’d buy at a big-box store. If you’re doing photo editing or just like crisp text, the 4K model is the only one worth your time.
Why Everyone Hates the Stock Hard Drive
We need to talk about the "spinning rust" problem.
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Many iMac 21.5 inch 2017 units shipped with a 1TB 5400-rpm hard drive. It was a terrible decision by Apple even back then. macOS is an operating system designed for solid-state speed. When you try to run it on a mechanical platter that spins at 5400 rotations per minute, everything crawls. Apps bounce in the dock for thirty seconds. The boot time feels long enough to go make a sandwich.
Then there was the "Fusion Drive." Apple tried to get clever by pairing a small amount of fast flash storage with a large, slow hard drive. It worked okay for a while. But as those drives age, they fail. Or they just get confused. If you find a 2017 iMac with a pure SSD, you’ve hit the jackpot. If it has a 1TB HDD, you are going to be miserable unless you are prepared to perform surgery on the machine or run your entire OS off an external Thunderbolt SSD.
The Hardware Inside: Kaby Lake and Graphics
Inside these machines, you’ll find 7th-generation Intel "Kaby Lake" processors.
The 4K models usually have quad-core chips. That’s a significant jump over the dual-core base models. For basic tasks—think Chrome with twenty tabs, Spotify, and some light Zoom calling—the quad-core i5 is still perfectly snappy. It’s not going to win any races against an M1 or M2 chip, obviously. But it’s functional.
Graphics were actually a decent step up for this year. The 4K models came with dedicated AMD Radeon Pro 555 or 560 GPUs. These aren't gaming powerhouses. Don't expect to play Cyberpunk 2077 on this. However, for hardware-accelerated video rendering or basic 1080p video editing in Final Cut Pro, those dedicated cards make a huge difference compared to the integrated Intel graphics found in the cheaper versions.
Memory and the "Apple Tax" on Upgrades
Here is the bad news. Unlike the 27-inch model from the same year, the iMac 21.5 inch 2017 does not have a "trap door" for RAM.
If you want to upgrade the memory, you have to take the screen off. You have to cut the adhesive, remove the display panel, and essentially gut the machine to reach the SODIMM slots. It’s a nightmare. Most people shouldn't try it. Because of this, you should really look for a unit that already has 16GB of RAM. Trying to survive on 8GB in 2026 is a recipe for frustration, as the OS alone will eat up most of that.
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Software Support: The End of the Road?
This is where the reality check happens. Apple officially dropped support for the 2017 iMac with the release of macOS Sonoma.
Technically, the last official OS it supports is macOS Ventura. While Ventura is still getting security patches for now, the clock is ticking. You won't get the latest features like revamped Stage Manager or the newest Safari optimizations natively.
Now, there is a community-driven workaround called OpenCore Legacy Patcher (OCLP). It’s amazing. It allows you to run newer versions of macOS on unsupported hardware. I’ve seen 2017 iMacs running Sonoma and even newer builds quite well. But—and this is a big "but"—it requires some technical know-how. If you aren't comfortable tinkering with system-level EFI partitions, you’re stuck on Ventura.
Real-World Use Cases in 2026
Who is this computer actually for? It’s certainly not for "power users" anymore.
If you are a writer, a teacher, or someone who just needs a beautiful screen for emails and taxes, it’s great. The 4K display is stunning for watching Netflix or YouTube. The built-in speakers are surprisingly loud and full-bodied, much better than most budget laptops.
It’s also a fantastic "kitchen computer" or a secondary station for kids to do homework. Since the 2017 model has Thunderbolt 3 (USB-C) ports, it actually plays well with modern peripherals. You can plug in a fast external NVMe drive, and suddenly that slow internal hard drive doesn't matter anymore. You just boot from the external drive and the machine feels five years younger.
The Thermal Reality
One thing nobody tells you is that these things can get loud. The 21.5-inch chassis is cramped. When the Intel CPU starts working hard, the fan kicks in with a high-pitched whir. It’s not a dealbreaker, but if you’re used to the dead silence of a modern MacBook Air, the constant hum might annoy you.
Comparing the Options
When you’re browsing listings, you’ll see prices ranging from $150 to $400.
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- Avoid: The 2.3GHz dual-core i5 with the 1080p screen. It's just too weak for 2026.
- The Sweet Spot: The 3.0GHz or 3.4GHz quad-core i5 with the 4K Retina display.
- The Unicorn: A 2017 4K model that someone already upgraded to an internal SSD and 16GB of RAM.
If you find that "unicorn" for under $250, it’s a steal. You're essentially paying for a high-end 4K monitor and getting a free computer inside it.
Common Failures to Watch For
The iMac 21.5 inch 2017 has a few known "growing pains" as it reaches nearly a decade of existence.
First, the screen hinges can sometimes go weak, though this was more common in the older 27-inch models. More importantly, check for "pink tinging" or ghosting around the edges of the 4K display. This is a sign of a failing LCD panel. Also, listen to the fan. If it sounds like a grinding pepper mill, the bearings are shot.
Lastly, check the ports. Thunderbolt 3 ports are sturdy, but the SD card slot on the back often collects dust and stops reading cards. It’s a small thing, but annoying if you’re a photographer.
Actionable Steps Before You Buy
If you’ve decided to pull the trigger on a 2017 iMac, do not just hand over the cash and walk away.
- Check the Serial Number: Go to Apple’s "Check Coverage" page. It will confirm exactly which model it is. Sellers often mislabel 1080p models as 4K.
- Verify the Drive: Open "About This Mac" and go to the Storage tab. If it says "SATA Disk" or "HDD," be prepared for it to be slow. If it says "Flash Storage," you're in business.
- The External SSD Trick: If you buy a slow one, buy a Samsung T7 or a similar external SSD. Use Carbon Copy Cloner to move the OS to that drive and set it as your startup disk. It's a 10-minute fix that changes the whole experience.
- Peripheral Check: Make sure it comes with the Magic Keyboard 2 and Magic Mouse 2 (the rechargeable ones). Buying those separately will cost you another $100+, which ruins the "budget" aspect of the purchase.
The iMac 21.5 inch 2017 is a legacy machine that still has a lot of heart. It’s the last of the "classic" small iMacs before the M1 redesign. While it’s officially on the sunset list for software, the hardware remains beautiful. Just make sure you aren't buying the low-end version, or you'll regret it within an hour of plugging it in.