Last week, Apple did something it never does—it spoke to journalists and pundits on the record about a product that was so far from being released that the company didn't even have prototypes to show off.

That's the state of the Mac desktop right now. After the October 2016 product came and went with no mention of the rumored desktops, complaints and anxiety about the state of Apple’s high-end computers reached a fever pitch (my barometer for this sort of thing is what John Siracusa, Marco Arment, and a handful of developers I follow say on their podcasts and Twitter feeds, which is highly unscientific, but I don't think that makes it inaccurate). Apple appeared to be pulling out of the external display business, and its new pro laptops offered less RAM and had worse battery life than some people were happy with. It had been a year since the iMac got an update, two years since the Mac Mini was updated, and more than three years since we heard a single peep about the Mac Pro.

In an internal memo a couple of months later, CEO Tim Cook said the company had “great desktops in his roadmap,” but that’s the stock boilerplate response to any questions about future products. Credible reports around the same time that suggested Apple had de-emphasized and slowed down Mac development internally only added fuel to the fire.

So, the unusual amount of uncertainty about desktops prompted an unusual response: a sit-down conversation about products that won’t be announced or released until later this year or next (or possibly even later than that). Apple declined to get very specific about its plans, but let’s sift through some tea leaves and suss out some possible directions that Apple’s desktops could take from here.

The Mac Pro, and admitting your mistakes

When Phil “can’t-innovate-my-ass” Schiller unveiled that new Mac Pro in mid-2013, surely the plan was not to let it sit and rot for three years before pledging to replace it with something completely different. At the time, Schiller said that Apple had wanted to build a new Mac Pro design that would last for "another ten years." But that’s not what happened, and Apple is willing to admit that it was because of engineering problems based on a poor prediction of where high-end computing was headed.

From Craig Federighi:

“I think we designed ourselves into a bit of a thermal corner, if you will. We designed a system that we thought with the kind of GPUs that at the time we thought we needed, and that we thought we could well serve with a two GPU architecture… that that was the thermal limit we needed, or the thermal capacity we needed. But workloads didn’t materialize to fit that as broadly as we hoped. Being able to put larger single GPUs required a different system architecture and more thermal capacity than that system was designed to accommodate. So it became fairly difficult to adjust.”

Specifically, the way the 2013 Pro was designed, each of the three boards on the inside (one with a CPU, two with dedicated GPUs) were meant to have roughly similar heat output and cooling needs. If you were to throw that balance off—by adding, say, a single more powerful GPU instead of two midrange ones—the fan wouldn’t be able to cool it off well enough.

The design assumed that GPU compute via APIs like OpenCL and Metal would be transformative, and it even defined APIs within macOS to make it possible to dedicate a single GPU solely to either OpenCL or OpenGL. Certainly, there are workloads for which that sort of thing is useful, but GPUs haven’t removed the need for fast multi-core CPUs. This is especially true of software developers, an audience Apple says is rapidly growing.

The 2013 Mac Pro was a one-size-fits-all mini computer that replaced a hulking but enormously flexible PC tower. The older Mac Pro towers could accept multiple high-end GPUs, they had two CPU sockets, they had a bunch of internal drive bays, they had internal PCI Express expansion slots. Thunderbolt can replace some of that with external drive caddies and other accessories, but it can’t let you fundamentally alter the system’s performance the way more CPU and GPU horsepower can (and Thunderbolt accessories are habitually rarer and more expensive than their standardized internal counterparts).

Apple acknowledges all of this. Read a transcript of the interview, and it’s clear that the company understands the key shortcomings of the trashcan Mac Pro design. Pros have many, many different needs. Pros need regular, consistent updates. Pros need modularity and flexibility and expandability.

Imagining what a new Mac Pro looks like

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iFixit

We won’t see this new Mac Pro until at least next year, and computing still moves quickly enough that it’s hard to predict exactly what Apple is going to settle on. But looking at what Apple acknowledged about the old Mac Pro design alongside its goals for the new one allows you to make some educated guesses.

Let’s assume, for the sake of argument, that Apple is still going to want to build something relatively small and unobtrusive, because this is Apple we’re talking about. There’s a whole bunch of space in the old cheese grater-style Mac Pro that could be saved if you were trying to modernize it: start by removing the 5.25-inch optical drive bays and also the internal 3.5-inch drive bays, both of which can easily be replaced by external USB or Thunderbolt or network-attached accessories. The small SSD cards that Apple already uses in the 2013 Mac Pros also save you from needing any internal storage bays; just make a little room on the motherboard (some PC motherboards even tuck the M.2 SSD slot away on the back of the board to save space on the front).

Further Reading Intel’s new Broadwell Xeon server CPUs offer up to 22 cores per socket

On the same note, I’d also bet against Apple including multiple processor sockets. This is both because of the amount of extra cooling and board space these configurations need (another socket plus four more RAM slots), and because technological advancements have made this less necessary than it was in the old days. The old dual-socket Mac Pros maxed out at 12 cores, or two CPUs with six cores apiece. By the time the 2013 Mac Pro had come out, Intel offered a single-socket CPU with 12 cores. Now Intel offers as many as 22 cores in a single CPU within a similar TDP; next-generation Xeons are said to be bumping that up to 28 or even 32. Those processors cost many pretty pennies, but the Mac Pro is hardly the most frugal of desktop computers.

The same thing is true of RAM slots, more or less. If you were using two processors, the old Mac Pro could handle up to 128GB using third-party RAM modules; the 2013 Mac Pro can do the same with four slots, and any new Mac Pro would likely be able to do at least that well depending on what CPU support and memory density looks like when it’s released.

GPUs are perhaps the biggest wildcard. Based on all of Apple’s talk about its dual-GPU system being the wrong move, I’d say the new Mac Pro will have the space and the cooling to accommodate at least one top-end 250W GPU. The question is whether Apple would use a proprietary card design like it does in the 2013 Mac Pro, or if it would return to using standard PCI Express cards. The former is more flexible but the latter requires less development work on Apple’s part, which I’d say is a plus if I was trying to keep a high-end computer up to date to satisfy a fraction of a fraction of my userbase. On the Accidental Tech Podcast, John Siracusa suggests that Apple could use standard PCI Express cards with custom cooling apparatuses installed, which seems like a good compromise.

Even if it does use standard GPUs, I wouldn’t hold my breath for much more internal expandability. Adding things like NICs and storage capacity is a place where Thunderbolt excels, and I’d guess that Thunderbolt 3’s wider adoption in the rest of the PC industry will lead to a more diverse, competitive accessory ecosystem. Adding, say, 10 gigabit Ethernet to a 2013 Mac Pro via Thunderbolt costs a few hundred bucks, while adding it via PCI Express can be done for less than half that price. If you can close that gap, lack of internal expandability for peripherals won’t be such a huge deal.

Put all of this stuff—one CPU socket that can scale from 4 to over 20 cores, four RAM slots, a top-end GPU, a fast SSD card, and plenty of Thunderbolt 3 ports for additional expansion—inside a relatively small, sleek case, and then make it pretty easy for users to open up and work on themselves, and you’ve got a Mac Pro that should serve a wider base of users than the 2013 model while still keeping people who liked that model’s size and unobtrusiveness reasonably happy. Apple could choose to go another way—it could definitely choose to make a larger, more expandable system than I’m assuming here—and none of my calculus takes bleeding-edge technology like DDR5 or Intel’s Optane into account. But if the old Mac Pro was designed to be as flexible as possible and the 2013 Mac Pro was engineered in part to make a statement about innovation at Apple, a computer like this could find a way to do both.