iMac 21.5-inch 2015, 2017 and 2019: Upgrades, Repairs and Specs

The 21.5-inch iMacs from Late 2015, 2017 and 2019 look almost identical, but they upgrade very differently. The 2017 and 2019 take both an SSD and more memory, and with those fitted they remain useful everyday computers. The Late 2015 has its memory soldered to the logic board, so an SSD is the only upgrade that changes much. We do this work at our workshop near Castle Hill, with SSD upgrades from $599.

Every model here has a laminated display held on with adhesive, so any job inside means cutting the adhesive and fitting new strips. Other generations are on our iMac repair and upgrades hub.

How to identify your 21.5-inch iMac

• About This Mac. Choose it from the Apple menu. The name shown, such as “iMac (Retina 4K, 21.5-inch, 2017)”, gives the year, and “Retina 4K” separates the 4K models from the standard ones.
• Model Identifier. Hold Option while opening the Apple menu, then pick System Information. Hardware Overview shows an identifier such as iMac18,2, which decides RAM limits and macOS options.
• Underside of the stand. The serial number, EMC number and A-number are printed under the foot. A2116 means a 2019 4K, but A1418 appears on every 21.5-inch iMac from Late 2012 to 2017, so on its own it does not give the year. The serial number, entered at checkcoverage.apple.com, does.

One wrinkle: Apple lists the standard Late 2015 as iMac16,1, but independent references report that its 2.8GHz version shows iMac16,2, like the 4K. Check the full name in About This Mac before ordering parts.

Specs and identity by year

“Apple” is Apple’s supported maximum; “OWC” is the larger kit the memory maker OWC sells for that model.

Upgrades: what each year can take

SSD: the upgrade that matters on every model

Most of these iMacs left the factory with a 1TB hard drive or Fusion Drive. The exception is later 2019s: Apple made a 256GB SSD standard on that model from 4 August 2020. If yours still has its original drive, replacing it is the biggest single improvement: startup, app launches and updates are dramatically faster. Our iMac SSD upgrade costs from $599 including a 500GB SSD, data transfer and macOS setup, or from $699 with 1TB.

• The blade connector may not exist. These 21.5-inch models only have the PCIe blade SSD connector if they left the factory with a Fusion Drive or SSD. iFixit’s teardown of a hard-drive 4K Late 2015 found it missing. On those units the SSD goes in the 2.5-inch SATA bay instead.
• The Fusion Drives hold very little flash. A 1TB Fusion Drive has just 24GB of flash in a Late 2015, and 32GB in the standard 2017 and the 2019 4K. Everything else comes off the mechanical drive, and Apple’s APFS file system, designed mainly for SSDs, gets slower on a hard disk over weeks and months. So a Fusion iMac can feel no quicker than a hard-drive one.
• A Fusion Drive is two drives acting as one. If either half fails or is replaced, macOS sees two drives, and Apple’s reset to rejoin them erases everything on both. We copy your files off first.

RAM: yes on the 2017 and 2019, never on the Late 2015

The 2017 and 2019 have two standard SO-DIMM slots, but they sit behind the logic board, so reaching them means taking the display off and lifting the board out. Our RAM upgrade with 16GB is from $449 on its own, or from $249 extra alongside an SSD, because the display only comes off once.

Both Late 2015 models have soldered memory that Apple lists as not upgradeable. Each keeps whatever it was built with, 8GB or 16GB, so check About This Mac before buying one second-hand.

Checks you can do before paying anyone

• In System Information, select Storage and look at the medium type. “Rotational” means a hard drive, and an SSD will help.
• In Activity Monitor’s Memory tab, watch the Memory Pressure graph while you work. Mostly green means RAM is not your bottleneck; yellow or red means it is.

macOS: Apple’s ceiling and what the patcher adds

Apple stopped at Monterey 12 for both Late 2015 models, Ventura 13 for the 2017s and Sequoia 15 for the 2019. On Monterey, Chrome has stopped updating (version 150 was the last), Microsoft 365 no longer updates and Safari is stuck on version 17. Ventura still gets current Chrome, but its last Apple security update came in August 2025.

OpenCore Legacy Patcher takes the Late 2015 and 2017 models to Sequoia. The 2017s have native graphics support, so they need only the Wi-Fi patches and relaxed security settings. The Late 2015s rely on Legacy Metal graphics patches, which leave known gaps, such as DRM-protected video that may not play in Safari on Sonoma and later. On the 2019 the patcher gains you nothing: Sequoia is already its official ceiling, and the patcher has no Tahoe support.

• System Integrity Protection must be lowered, and it stays that way.
• Every macOS update removes the patches, so they must be reapplied, and automatic updates need to stay off.
• By Apple’s usual pattern, Sequoia is in its final year of security updates, which points to about September 2027.

Our patcher install is from $249, including post-install checks; app-by-app detail is on newer macOS on an old iMac. On a hard-drive iMac, fit the SSD first: a heavier macOS on a spinning disk is a poor experience.

Known faults on these models

• Slowness. Start with the original 5400rpm drive or small-flash Fusion Drive; our guide to an iMac running slow covers the other causes.
• A Fusion Drive that has split in two. The iMac then shows two drives. If the drive is still readable, data recovery is from $249.
• Dark smudges inside the screen. A class action filed in 2018 claimed that iMacs made from 2013 to 2018 have no dust filters, so dust gets inside the display; its outcome is not confirmed. Wiping the glass will not shift it.
• No power or random shutdowns. Our $150 bench diagnostic is waived if you go ahead with the repair. A 21.5-inch power supply is from $399 and board-level repair from $449; see logic board and power supply repair.
• Cracked screens. Glass and LCD are bonded into one part, so a crack means a new display assembly. A 4K display is from $749 on the 2015 and 2017 and from $799 on the 2019; see iMac screen replacement.

Worth the money or not: the numbers

On Gumtree in September 2026, sellers were asking a median of about $500 for a working 2017 4K, across five listings from $190 to $590. The 2019 4K had only two listings, at $275 and $400; the Late 2015 and standard 2017 had too few to quote. For comparison, a new 24-inch M4 iMac costs $2,399.

• 2017 or 2019 on a hard drive or Fusion Drive: worth it if you are keeping it. A 500GB SSD and 16GB of RAM in one visit start from $848 (SSD from $599, RAM from $249 extra), or from $948 with 1TB. The 500GB combination is about a third of the price of a new M4 but more than a working 2017 4K is advertised for, and two to three times the 2019 4K listings: the price of keeping a machine you like, not money you get back on sale. A 2017 can add Sequoia from $249, for a total from $1,097.
• Late 2015: only for lighter use, on a machine you are keeping. The SSD and the patcher are the only useful spend, from $848 together, more than a working 2017 4K. If it has 8GB and you run heavy apps, put the money towards something newer.
• 4K screen replacement: usually not worth it. From $749 on a 2017 4K advertised at about $500, or from $799 on a 2019 that may fetch $275 to $400, the screen costs more than the machine is worth. Unless the rest of the iMac was recently upgraded, rescue the data and put the money towards a replacement.

Compare other models in repair or replace an old iMac.

Bringing it in

We take iMacs by drop-off only, at our workshop near Castle Hill, Monday to Saturday, 8am to 6pm. Customers come from the Hills District and all over Western Sydney. SSD and RAM work usually takes one to two business days when parts are in stock, with a 12-month warranty on parts and labour.

Call 0400 454 859

Other generations: the 21.5-inch iMac 2012–2014, the 27-inch 5K 2014–2017 and the 27-inch 5K 2019–2020.

Questions

Is a 2017 iMac still worth using in 2026?

For everyday work, yes, provided it has an SSD. A 2017 on its original hard drive or Fusion Drive feels slow on any recent macOS, and Apple's support stops at Ventura, which no longer receives security updates. With an SSD, 16GB of RAM and Sequoia installed through OpenCore Legacy Patcher, it remains a capable machine for browsing, email, documents and photos. Budget from $1,097 for all three with a 500GB SSD, more than twice its resale value, so it suits a machine you plan to keep.

Can you upgrade the RAM on a 2015 iMac 21.5-inch?

No. Both Late 2015 21.5-inch models, the standard one and the Retina 4K, have their memory soldered to the logic board. Apple offered 16GB only as a build-to-order option when the iMac was new, so a machine sold with 8GB will always have 8GB. What you can still change is the storage: replacing the hard drive or Fusion Drive with an SSD is from $599.

Does the 2019 21.5-inch iMac get macOS Tahoe?

No. Apple's support for the Retina 4K 21.5-inch 2019 ends at Sequoia 15, and Tahoe runs on only one Intel iMac, the 27-inch 2020. OpenCore Legacy Patcher cannot help, because it supports macOS only up to Sequoia and has no Tahoe release. Going by Apple's usual pattern, Sequoia should keep receiving security updates until around September 2027.

Can you replace just the glass on a 21.5-inch 4K iMac?

No. From Late 2012 on, Apple bonds the front glass to the LCD panel, so they are one part. Cracked glass therefore means a new display assembly, from $749 on a 2015 or 2017 4K and from $799 on a 2019. The separate glass repair we offer from $199 applies only to 2009 to 2011 iMacs.

How much does it cost to upgrade a 2017 iMac 21.5-inch?

An SSD with 500GB is from $599 including data transfer and macOS setup, or from $699 with 1TB. RAM needs the display and logic board out, so on its own it is from $449 with 16GB, but from $249 extra when done with the SSD. Doing both at once costs from $848 with the 500GB SSD. Newer macOS through OpenCore Legacy Patcher is from $249.

Should I buy a used 2019 iMac 21.5-inch?

At the right price it can be a sensible buy, because it is the only model in this group Apple still supports. Check the storage first: units built before August 2020 normally have a 1TB hard drive or Fusion Drive, while later ones came with a 256GB SSD as standard. An SSD and RAM cost from $848 if it still has a hard drive, more than these are listed for, so one that already has an SSD is usually the better buy. Sequoia's updates should end around September 2027.