AMD Ryzen 9 3900X vs. Intel Core i9-9900K: Which High-End CPU to Buy?

With the arrival of the first Ryzen 9 processors in 2019, AMD expanded its ability to rival the performance of competing Core i7 and Core i9 chips from Intel. If you're in the market for the ultimate high-performance, consumer-grade desktop CPU, the Ryzen 9 and Core i9 are both compelling options. In 2021, new second-generation Ryzen 9s in the Ryzen 5000 Series (headed up by the ferociously powerful 16-core AMD Ryzen 9 5950X) have taken the fight to the latest Core i9s. (The Core i9 is now in the 10th and 11th Generations on a new-for-2020 platform, the LGA1200.)

But here in 2021, silicon shortages have flipped the market around since the first Ryzen 9 chips hit the scene. Here in the spring of 2021, it can be tricky to find the new Ryzen 9 5000 Series processors at or below list price—or indeed, in stock at all. As a result, in some cases, it may make more sense to look at a previous-generation chip, especially if you already have a compatible motherboard. (Intel's newest top Core i9s, the Core i9-10900K and Core i9-11900K, are a bit more readily available, but prices remain high.)

So the Core i9-versus-Ryzen 9 dynamic has changed since the introduction of the 2019-era chips. You'll still have to choose one or the other, of course. Even if you could swap them in and out of your desktop PC on the fly (and of course, you can't; they use wholly different sockets and therefore motherboards), at a $500 list price for each of the flagship versions—the Ryzen 9 3900X and the Core i9-9900K—buying both would be prohibitively expensive. So let's take a look at which of these chips comes out on top, depending on how you plan to use your PC.

Comparing Key Specs: Ryzen 9 3900X vs. Core i9-9900K

The Ryzen 9 3900X has 12 cores to the Core i9-9900K's eight, so it gains the upper hand right from the beginning, at least as far as raw specs are concerned for multi-threaded workloads. All else being equal, the more cores a chip has, the better it is able to handle complex workflows from modern software applications, many of which are designed to assign tasks to as many CPU cores and threads as they can lay hands on.

Both chips have multi-threading support, which means that each core can handle two instruction threads from software simultaneously. So the Ryzen 9 3900X can handle 24 instruction threads, while the Core i9-9900K can handle 16. Again, if your software of choice is optimized to parcel out tasks to as many processing threads as it can, more is better here.

Based purely on core and thread count, then, the Ryzen 9 3900X is a likely better choice than the Core i9-9900K for 3D animation work, video editing, and other workflows dependent on a chip's core count.

Many other tasks, especially common ones like playing older games or browsing the web, are heavily influenced by other factors, including a chip's clock speed or the size of its cache, or other hardware such as your video card. The Core i9-9900K has a base frequency of 3.6GHz and a maximum boost frequency of 5GHz, compared with the Ryzen 9 3900X's base 3.8GHz speed and 4.6GHz maximum boost. Both can be overclocked.

The speed differences are small but significant, although you can't strictly compare them one to one. Assuming you are able to pair each chip with a cooling solution that offers enough thermal headroom for sustained maximum clock speeds, the Core i9-9900K might offer a slight advantage on "bursty" workflows like applying a filter to an image in Adobe Photoshop. Of course, if speed on that same task would be offset by having more cores and threads in the first place, that slight advantage in clock rates might matter less. It all comes down to the traits of the individual program, and that is where more granular benchmark testing comes in. (More about that in a minute.)

Beyond clock speed and core count, many gamers will also want to pay attention to a chip's cache and its peak supported memory speed, since the performance of some games can be dependent on a CPU's ability to access memory, especially at screen resolutions below 4K. (When you are playing at the very highest resolutions and detail settings, the GPU's capabilities tend to be the performance limiter more than the CPU.)

Here, at least on pure specs, the Ryzen 9 3900X wins hands down. It comes with support for 3,200MHz DDR4 memory and a whopping 70MB L3 cache on the die. The Core i9-9900K has lower peak official memory-speed support (2,666MHz) and a much smaller 16MB of L3 cache. But there's more to this argument than just spec numbers.

Translating Specs to Real-World Performance: CPU

While a comparison of specs suggests that the Ryzen 9 3900X comes out on top in a bunch of seminal areas, real-world performance doesn't always reflect this.

On our Cinebench R15 test, which includes both single-core and multi-core workflows, the Ryzen 9 far outpaces the Core i9 when it's using all of its cores and threads. That's a perfectly natural outcome, since the Ryzen 9 has more of them. (Again, that's 12 cores/24 threads for the Ryzen 9, versus eight cores/16 threads for the Core i9.) But the AMD chip is actually slightly behind its Intel competitor when it comes to single-core performance.

When it comes to encoding a 12-minute 4K video to 1080p using the open-source Handbrake app, the difference between the Core i9-9900K and the Ryzen 9 3900X is no small difference, either...

The Ryzen comes out about 25 percent ahead. Beyond this head-to-head chart, even more important on this test are the relative differences in performance as you climb the product ladders of AMD's and Intel's mainstream chip lines. The Ryzen 9 3900X is predictably faster than the Ryzen 7 3700X, and much faster than the previous-generation Core i7-8700K and Ryzen 5 2600X. (Check out our full review of the Ryzen 9 3900X for a more detailed breakout of the scores versus other CPUs.)

The same relative performance is borne out in our POV-Ray test, another CPU-burner that has both single-core and multicore aspects...

Once again, the Core i9 prevails on the single-core task but falls a bit behind on the multicore one (though by a bit less time, proportionally, than on Handbrake and Cinebench).

Finally, a quick real-world task: a workout in 7-Zip, a commonly used file compression/decompression program...

Again, about a 25 percent advantage for the Ryzen 9. When the software in question is maximizing the use of cores and threads, the Ryzen 9 generally will prevail.

Translating Specs to Real-World Performance: Graphics

The performance picture is more nuanced when it comes to playing demanding 3D games in concert with these two killer CPUs. We tested the two chips with an Nvdia GeForce RTX 2080 Ti video card installed in our respective testbeds. The RTX 2080 Ti was the highest-end consumer video card available when these CPUs debuted, and was used here to eliminate, as far as possible, the graphics card as a performance bottleneck.

One key issue to raise here: integrated graphics, or the lack thereof. The Ryzen 9 3900X has no on-chip graphics and demands a companion video card, full stop. The Core i9-9900K, in contrast, incorporates Intel's light-hitting UHD Graphics integrated silicon, though, for gamers, this CPU will certainly be paired with a dedicated video card. But if you just want raw CPU muscle and don't have or want to buy a video card, the Core i9-9900K is your chip between these two. (Note: Intel also sells a slightly cheaper variant of this chip, the Core i9-9900KF, that is identical but has the integrated graphics disabled.) Considering that video card prices have skyrocketed in 2021, the presence (or not) of integrated graphics is no small consideration if you are not a PC gamer or a creative pro who needs the kind of GPU acceleration that only a dedicated video card can deliver.

One of the concerns with the earlier generations of AMD Ryzen CPUs is that with certain combinations of monitor resolution and video card (notably, with high-end video cards at lower resolutions, like 1080p), the Ryzens registered lower frame rates versus using the same cards and settings with competing, comparable Intel Core CPUs. This situation improved with the second-generation Ryzen chips and is showing further narrowing with generation three.

Here's a peek at the results we saw with the Ryzen 9 3900X versus the Core i9-9900K (as well as two other chips in their class) with a host of games on the RTX 2080 Ti and a synthetic benchmark...

As you can see, the results at 4K resolution on the games are largely the same across the CPUs. With the games at 1080p, on the other hand, it's more of a mix. That said, in this specific test set, the Core i9-9900K holds a commanding frame-rate lead in only a few situations. For example, on the AAA title Far Cry 5, the Ryzen 9 3900X scored 18 frames per second (fps) lower than the Core i9-9900K did, a difference of about 13 percent. We saw smaller deficits on older games like Bioshock Infinite and Hitman: Absolution. Meanwhile, on one classic, less-demanding esports favorite (Counter Strike: Global Offensive), the Ryzen 9 3900X outperformed its main Intel competitor.

In most cases, these small performance differences won't matter and will be edge cases. Both the Ryzen and Intel chips, paired with a high-end video card, are capable, depending on the game, of driving frame rates in excess of the 144Hz, 240Hz, or 360Hz that even the highest-end gaming monitors can display. Still, the differences we found in our testing are an important reminder that specs alone don't tell the whole story when you're comparing two CPUs for gaming or content creation.

It's also worth noting that the Ryzen 5000 Series chips have achieved near parity with current Intel chips on 1080p gaming. Check out our review, for example, of the very new Core i9-11900K for the latest gaming numbers encompassing the Core i9-9900K and the Ryzen 9 3900X, as well as the latest 11th Gen Intel and Ryzen 5000 AMD chips.

Getting on the PCI Express Train

Besides raw specs and performance benchmarks, there are several differences in the feature sets for the respective Ryzen 9 and Core i9 platforms that might factor into your buying decision.

All of AMD's third-generation Ryzen chips (and the new Ryzen 5000s) include support for PCI Express 4.0. This cutting-edge system-level bus offers added bandwidth for video cards (which is of no immediate importance) and storage components like SSDs (a little more relevant today). SSDs that support the new PCI Express 4.0 standard are now on the market, which could make the Ryzen 9 3900X a better pick if you're also planning on upgrading your storage drive in the near future, or are building a PC from scratch with an eye toward future-proofing.

Note: To gain support for PCI Express 4.0, you'll also need a new AMD X570-chipset-based motherboard along with your Ryzen 9 3900X chip. An older AMD AM4-socket board may support this new CPU, but it won't enable PCI Express 4.0 speeds on its expansion slots or M.2 slots.

Although the Z390 motherboard platform that debuted in concert with the Core i9-9900K doesn't support PCI Express 4.0, a few boards do integrate the Thunderbolt 3 interface for connecting external peripherals at speeds of up to 40GBps. This is something the Ryzen 9 3900X lacks (Thunderbolt 3 is not a core thing on AMD desktop platforms), and it could be a deal breaker if you are a professional content creator with lots of Thunderbolt 3 peripherals.

Intel CPU platforms have only added PCI Express 4.0 support with the Z590 chipset, new in 2021, though a few older boards from the Z490 family can support PCIe 4.0 with updates and an 11th Generation CPU. Whether future AMD CPU platforms will get Thunderbolt 3 via new supporting chipsets in the years to come remains to be seen. So, if you really need support for both, it may be worth waiting.

Pricing It Out

Most of the comparisons above presuppose that you're interested in buying one of these chips by itself, to install in a new PC or to upgrade an existing one. Many of the comparisons also apply if you're looking at buying a pre-built system with a Ryzen 9 3900X or Core i9-9900K. If you are shopping in 2021, though, pre-built PCs will have likely given way to 10th or 11th Generation Intel Core chips, and some will have adopted the Ryzen 5000.

As with most things in life, money is perhaps the most important point of distinction whether you're upgrading, building from scratch, or buying pre-built. With their $500 list prices, both of these CPUs are pretty expensive in absolute terms. (Sure, you can find server-grade and enthusiast CPUs that cost more than $1,000, but those are way outside most shoppers' budgets and needs.) And because they're priced identically, neither has a clear advantage here on that front. Of course, given the volatility of the CPU market in 2021, those list prices emphasize the "suggested" in "manufacturer's suggested retail price." But the prices of the Ryzen 3000 Series and the 9th and 10th Generation Intel Core chips have stayed more stable than their newest successors.

You may need to factor in the price of a new motherboard and cooler to support these chips, however. The Core i9-9900K requires a Z390 motherboard, which you probably don't already own if you're considering a chip of this class and is now confirmed as a dead-end platform. (The socket it requires, LGA1151 Revision 2, is no longer used by the 10th and 11th Generation Cores from Intel, and even the socket used by those, LGA1200, will dead-end after the 11th Generation.) The Ryzen 9 3900X works with most AM4-socket motherboards (older ones, only after a BIOS upgrade), but you'll need a current-generation board based on the AMD X570 chipset one to unlock all of its features, including PCI Express 4.0 support. (X570 boards at this writing started at around $150.)

The CPU cooling is a key distinction, as well, and a possible cost booster. The Ryzen 9 3900X comes with AMD's stock cooler in the box, a nifty, RGB LED-ringed cooler called the AMD Wraith Prism, pictured above. It's not a fancy liquid cooler, but it's included in the cost of the CPU. The Core i9-9900K, on the other hand, comes as the chip alone, with no CPU cooler in the box. You'll need to add your own, and Intel generally recommends a liquid cooler. Later Ryzen 9 5000 chips also ask you to Bring Your Own Cooler.

If you don't own one, you're looking at $75 to $100 for a basic single-fan, sealed-loop all-in-one liquid cooler, and you'll want to be sure your case has the room for installing it. A few makers, such as Noctua, offer air coolers rated to keep the Core i9-9900K cool. But if you want to run it (or the Ryzen 9, for that matter) at peak speeds for sustained periods or overclocked, you'll want to go liquid.

Bottom Line: For Most, the Ryzen 9

Factoring in specs, performance, price, and ancillary features, neither chip leaves the other in its dust when it comes to gaming and graphics performance. We'd still give a slight edge to the Core i9-9900K if sheer game frame rates are all that drives you. On the raw CPU-muscle side of things, though, for applications that can hit all cores, the Ryzen 9 3900X does have an edge in many cases, which is why it's an Editors' Choice pick among high-end CPUs.

With more cores and support for more addressable threads, higher memory speeds, and a larger cache, this CPU has an advantage on paper, and indeed is the better choice if you can leverage those extra cores for no extra money. Of course, if latest-gen CPU prices return to earth in the near future, we'd also recommend looking into its Ryzen 9 5900X successor, especially if you are a hard-core gamer who also happens to need all the cores and threads you can get.