Why the Mac Pro lacks upgradable RAM and support for eGPUs


2023 Mac Pro with Apple M2 Ultra
The 2023 Mac Pro has an inescapable limitation.
Photo: Apple/Cult of Mac

The just-launched 2023 Mac Pro lacks features considered critical for workstations: upgradable RAM and support for eGPUs. But this isn’t Apple blindly making an error — it’s an inescapable fact of the M-series’ unified memory architecture.

The limitation isn’t new: it’s been known since the M1 processor was announced. But Tuesday’s release of a top-tier macOS workstation shines a spotlight on the problem.

For those who weren’t paying attention back in 2020, here’s an explanation of why RAM upgrades and plug-in GPU aren’t an option for the 2023 Mac Pro.

Graphics professionals expect RAM upgrades and eGPUs for workstations

Consumers like high-end computers — a faster computer is easier to use. But graphics professionals absolutely require the most performance they can get. Rendering large amounts of high-resolution 3D animation takes powerful computer resources. Slow computers can be the difference between a profitable video production company and bankruptcy.

A graphics workstation requires a blazing-fast processor, of course. But a truckload of RAM is necessary too, and maybe an eGPU, too. Which is why it’s a big deal that the 2023 doesn’t offer user-upgradable RAM or eGPU support.

It’s something graphics pros have been through before. The 2017 iMac Pro lasted for a mere three years of lackluster sales before being discontinued, partially because RAM upgrades required an expert to disassemble the computer.

But one would have thought Apple learned its lesson. Consider the 2019 Mac Pro — upgrading its RAM is as easy as plugging in the chips. Adding an eGPU to that computer is just as simple. But that workstation uses an Intel processor, not Apple silicon. And Cupertino set itself up to repeat the mistakes of the iMac Pro in its next workstation.

Understanding the Mac unified memory architecture

Understanding why 2023 Mac Pro RAM and GPU upgrades are impossible requires diving into the M-series’ unified memory architecture. As Apple put it back in 2020 when the first M-series chip launched, “Macs and PCs have traditionally used multiple chips for the CPU, I/O, security, and more. Now with M1, these technologies are combined into a single SoC, delivering a whole new level of integration for greater performance and power efficiency.”

In somewhat less technical terms, the M1 and M2 are more than simply a Central Processing Unit. The Graphics Processing Unit is also built in. As is the RAM. These are all integrated parts of the System on a Chip.

It’s the secret to the extremely fast performance of the M series. Data moves more quickly between the components built into the chip that it can between separate processor, RAM and GPU chips. Plus, the unified memory architecture “allows all of the technologies in the SoC to access the same data without copying it between multiple pools of memory, further improving performance and efficiency.”

The weakness of the architecture is that individual components can’t be upgraded. It’s not possible to add more RAM to the SoC, or swap out the GPU.

While it’s theoretically possible to add more RAM off the chip, this would not take advantage of the significant speed boost that comes from memory built into the chip. In short, this add-on RAM would slow down performance, the opposite of the reason why it’s being added. That’s likely why Apple doesn’t offer the option.

The same problem affects external graphics processing units, called eGPUs. Apple used to sell these for Intel-based Macs but has since stopped because they aren’t compatible with the M series.

Perfect for MacBook but bad for Mac Pro

To be clear, the unified memory architecture isn’t flawed. It’s what allows Apple to offer MacBooks with excellent performance paired with long battery life. And MacBooks make up the lion’s share of Mac sales.

The challenge is that battery life is immaterial to workstations. They need maximum performance. And while that means the M-series isn’t particularly well suited for top-of-the line professional desktops, that’s a niche business.

Apple surely made that calculation when it adopted the M series. It picked the option that benefited the most users.

Have the 2023 Mac Pro preconfigured with plenty of RAM

Cupertino had to know the unified memory architecture was going to be a problem for its workstations long before the M1 was unveiled. But there’s no simple way around the limitation — the difficulty is built into the processor.

Apple’s solution is enabling buyers to preconfigure the 2023 Mac Pro with a very powerful processor that included a very high-speed GPU built in, as well as tons of RAM. The top-tier M2 Ultra chip includes 24 CPU cores and a 76-core GPU and can be up configured with to 192GB of RAM.

Serious graphics pros should consider maxing everything out. Especially considering the Intel-based 2019 Mac Pro supports up to 1.5TB of RAM.

Is it working?

Apple claimed at the launch of the new computer, “Every Mac Pro has the performance of not just one but seven Afterburner cards built in.” These are cards Apple created to speed up workflows for video pros working with gigantic ProRes and ProRes RAW files.

And Geekbench 5 scores do show a huge increase. The new model pulled in a 21,402 on the multi-core test, compared to 10,390 for the 2019 version.

But data from Cinebench R23 isn’t so impressive. The 2023 Mac Pro reportedly scored 28,967 on this graphics benchmarking tool, while the 2019 version with an Intel Xeon W-3275M processor got a 28,051 score. That’s a mere 3% improvement.

It seems unfortunate that Apple nixed a rumored M2 Extreme configuration that would have come with 48 CPU cores, a 152-core GPU and up to 384GB RAM (a pair of M2 Ultras grafted together).

PCIe is still there

The 2023 Mac Pro can be preconfigured with an 8TB SSD, but that’s not enough for some graphics professionals. The new tower has six full-length PCI Express gen 4 slots available. That’s two x16 slots and four x8 slots, and these make making plugging in high-speed SSDs easy.

That said, the uber-Mac also has eight Thunderbolt 4 (USB-C) ports that support data transfers at up to 40Gbps. That’s going to be enough for many people, even lots of graphics pros.

Will graphics pros jump on 2023 Mac Pro?

Whether these heavy-duty, non-upgradable processors will satisfy graphics professionals won’t be known until we find out how much demand there is for 2023 Mac Pro.

Still, the fact that there’s already a wait for the new macOS tower is a sign that there’s pent-up demand for it.

This article was originally published in February 2023 and was updated at the release of the 2023 Mac Pro with additional information.


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