Mac Pro and Intel iMac RAM Upgrades: More Memory, Bigger Performance, Lower Cost Than Apple
There are two types of Mac users who are sitting on untapped performance right now: people with an Intel iMac from 2017 to 2020, and people with a 2019 Mac Pro. Both machines have user-upgradeable RAM. Both were regularly shipped with less memory than they're capable of running. And in both cases, adding more RAM is one of the most cost-effective upgrades you can make — dramatically improving multitasking, creative application performance, and overall responsiveness without replacing the machine.
This guide covers what's possible, what to buy, and what the installation involves for each.
Intel iMac RAM Upgrades (2017–2020, 27-inch)
The 27-inch Intel iMac is one of the most upgrade-friendly Macs Apple ever made. The RAM is accessible via a panel on the back of the machine — no tools required, no screen removal, no adhesive. Press the button, the panel opens, and you have access to four SO-DIMM slots. It takes about five minutes.
The 21.5-inch Intel iMac is a different matter — the RAM requires opening the display, which is considerably more involved. For 21.5-inch owners, we'd recommend getting in touch before attempting it.
Which iMac Models Have Upgradeable RAM?
- iMac 27-inch (2017): DDR4 2400MHz SO-DIMMs, 4 slots, up to 64GB
- iMac 27-inch (2019): DDR4 2666MHz SO-DIMMs, 4 slots, up to 128GB
- iMac 27-inch (2020): DDR4 2666MHz SO-DIMMs, 4 slots, up to 128GB
The M1 and M3 iMacs (24-inch) have unified memory that is soldered and cannot be upgraded. This guide applies only to Intel iMac models.
What RAM to Buy
The OWC 8GB DDR4 2400MHz SO-DIMM is compatible with the 2017 iMac models, and the OWC 16GB DDR4 2666MHz kit (2 x 8GB) is compatible with the 2017, 2019, and 2020 27-inch iMac models. All OWC memory is lab-tested for Mac compatibility and backed by a lifetime warranty — not the 1-year coverage most third-party RAM carries.
For a 2019 or 2020 iMac that shipped with 8GB, upgrading to 32GB (4 x 8GB) or 64GB (4 x 16GB) makes a very noticeable difference in real-world use. Applications like Final Cut Pro, Logic Pro, Lightroom, and Photoshop all benefit directly from more available RAM — fewer delays, smoother playback, more projects open simultaneously.
How to Install It
On the 27-inch iMac, this is genuinely straightforward:
- Shut down and unplug the iMac.
- Press the small button above the power socket on the back — the RAM door pops open.
- Pull the levers on either side of the existing modules to release them.
- Seat the new modules firmly until they click into place.
- Close the door and start up. macOS recognises the new RAM immediately.
OWC provides free installation videos for every compatible model. We have installation videos included on the product pages, under the Product Videos tab. The whole process takes under ten minutes.
Mac Pro 2019: RAM and Internal Storage Upgrades
The 2019 Mac Pro (tower and rack) is a different kind of machine — designed from the ground up for professional expansion. It supports user-upgradeable RAM (ECC RDIMMs, up to 1.5TB across 12 slots on the highest-end configurations), PCIe expansion cards, and aftermarket storage solutions.
Internal SSD Expansion: OWC Accelsior 8M2
The standout storage upgrade for the 2019 Mac Pro is the OWC Accelsior 8M2 or Sonnet Silent 8M2. It's a PCIe 4.0 x16 card with eight M.2 NVMe slots — fits directly into a full-height PCIe slot in the Mac Pro and delivers speeds up to 26,926 MB/s with all eight slots populated with NVMe SSDs. That's not a misprint. With SoftRAID XT included (OWC Accelsior card ONLY), you can configure RAID 0, 1, 4, 5, or 10 directly from the card. Available with SSDs installed or as a card-only option if you want to bring your own NVMe drives.
For a Mac Pro used in high-end video production, VFX, 3D rendering, or data-intensive research, this card eliminates storage as a bottleneck entirely. The 2019 Mac Pro has up to eight PCIe slots — you could install multiple Accelsior 8M2 or Sonnet Silent cards if the workflow demands it. It's compatible with both the 2019 Intel Mac Pro and the 2023 M2 Ultra Mac Pro.
A Note on Mac Pro RAM
The 2019 Mac Pro uses DDR4 ECC Registered DIMMs — a specialist memory type quite different from the SO-DIMMs used in the iMac. If you're looking to expand Mac Pro RAM, contact us directly with your current configuration and we'll advise on the right modules. The Mac Pro's memory system is more involved than a standard upgrade, particularly when mixing modules across all 12 slots.
RAM for 2019 Mac Pro (MacPro7,1), please see the link below. Due to ongoing worldwide shortage of flash components and with prices changing daily, we are unable to show prices for certain capacities in our shop. For any requirements, please Contact Us directly to discuss.
How Much Does It Cost vs Apple?
Apple no longer offers RAM upgrade options at checkout for the iMac — you configure at the time of purchase and that's it. But for machines you already own, aftermarket RAM from OWC costs a fraction of what Apple's own upgrades would have cost historically, and in many cases offers capacities Apple never made available at all. Going from 8GB to 64GB on a 2019 iMac with OWC RAM costs considerably less than Apple's original build-to-order prices for equivalent configurations.
The Mac Pro tells a similar story. Apple's official RAM upgrades at the time of purchase were priced aggressively. Aftermarket ECC RDIMMs from specialist suppliers bring the same performance at significantly lower cost.
Free Shipping to the UK and Ireland
All RAM and storage upgrades ship free to the UK in approximately 2 working days. Orders to Ireland over £100 include free shipping. Not sure which modules are right for your exact iMac or Mac Pro configuration? Get in touch before you order and we'll confirm compatibility.