AMD Ryzen 9 3900X and Ryzen 7 3700X Review: Zen 2 and 7nm Unleashed

AMD's launch of the Ryzen 3000 series processors marks an occasion that was nearly unthinkable a few short years ago: AMD has taken the process lead over Intel by fielding new 7nm processors that contain smaller and more densely-packed transistors than Intel's competing 14nm chips. The advantages of increased density come in the form of higher performance, better power efficiency, more cores, and more cache packed into a smaller area than the first-gen Ryzen models, all of which, as you can see in our CPU Benchmark Hierarchy, makes third-gen Ryzen a potent adversary for Intel both on the desktop and in the data center.

AMD paved the way for the 'Matisse' Ryzen 3000 series several years ago when it unveiled the revolutionary chiplet-based Zen microarchitecture. At the time, AMD laid out a roadmap that included a steady cadence of tick-tock-like updates interspersed with new revisions of the scalable microarchitecture. After the company's sophomore effort with the second-gen Ryzen processors, which featured a faster process paired with the same first-gen Zen design, the company is plowing forward with its Zen 2 architecture that AMD says offers up to 15% more instructions per cycle (IPC). Paired with the advantages of the 7nm process and more cores, not to mention AMD's trailblazing of the PCIe 4.0 interface on desktop platforms, the Ryzen 3000 chips promise an explosive step forward in performance.

AMD's first chips to come packing TSMC's 7nm process span the entire range of the mainstream desktop stack, but push core counts up from eight cores to 12 cores and 24 threads with the Ryzen 9 3900X we have in the lab today, upsetting the status quo and bringing mainstream platforms into what used to be the realm of the pricey high end desktop. If you're looking for something even beefier, AMD also recently released the 16-core Ryzen 9 3950X, which has taken our best CPU list by storm. 

Aside from those halo parts, AMD also has plenty of models that address the bulk of casual users, gamers, and enthusiasts, like the eight-core 16-thread Ryzen 7 3700X we also have in the lab, and a lineup of six-core 12-thread Ryzen 5 models. The Ryzen 7 3700X is particularly impressive with its combination of price and performance putting it squarely among the best gaming CPUs.

AMD is staying true to its enthusiast-friendly roots: Although you can pair the Ryzen 3000 chips with the new X570 chipset, they are also backward compatible with most AM4 socket motherboards. All of the models also come with beefy stock coolers, solder thermal interface material between the heat spreader and die to improve thermal transfer, and unlocked multipliers for easy overclocking. AMD even added support for auto-overclocking for mainstream processors. Pair that with the lower per-core pricing and the debut of the PCIe 4.0 interface for the desktop, and the Ryzen 3000 series appears to be a potent force.

AMD's ability to deliver on its optimistic roadmap in the waning light of Moore's Law is truly impressive, especially as we have become accustomed to never-ending cadences of incremental updates. But at the end of the day it all boils down to real-world performance. Let's see what the Ryzen 3000 series has in store. 

Ryzen 9 3900X

Make no mistake - from a core count perspective, the $500 12-core 24-thread Ryzen 9 3900X really has no comparison on the mainstream desktop. We have to reach up to Intel's high end desktop (HEDT) platform to find a fair comparison based on core counts. Intel's Core i9-9920X slots in with 12 cores and 24-threads for $1,199, a $700 premium over AMD's Ryzen 9 3900X.

There's no doubt the 3900X also blurs the line between the AMD's own HEDT Threadripper platform and the mainstream desktop: The Threadripper 1920X is AMD's only core-comparable processor. That processors has its own advantages, like access to 64 lanes of PCIe 3.0, and like the -9920X, it supports quad-channel memory. But both company's HEDT chips are much more expensive than the 3900X and require pricey HEDT motherboards.

Back in the familiar realm of the mainstream desktop, Intel's $488 Core i9-9900K serves as the 3900X's primary competitor. The -9900K comes with four fewer cores and eight fewer threads than the 3900X, marking a distinct difference in the price you pay per thread, but the -9900K does hold the clock speed advantage. AMD hopes to offset that advantage with its increased IPC throughput and the 3900X also supports the PCIe 4.0 interface with twice the bandwidth of the -9900K's PCIe 3.0 interface. You'll also notice the Core i9-9900K, known for its high power consumption and intense heat generation, has a lower 95W TDP than the 3900X's 105W rating. We can chalk that up to different measurement techniques. We'll provide extensive power and efficiency testing on the following pages to get a more accurate picture of actual power consumption.

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As pictured here, the 39000X comes packing AMD's Zen 2 microarchitecture spread across two small 7nm eight-core compute chiplets tied together with the Infinity Fabric interconnect via a larger 12nm I/O die (IOD). Each small 3900X compute chiplet, referred to as a CCD (Core Chiplet Die), comes with eight physical cores spread across two four-core Core Complexes (CCXes). Each CCX has 16MB of shared L3 cache, totaling 32MB of L3 cache per CCD, and 64MB of total cache for the entire chip. AMD disables two cores per CCD to create the 12-core 3900X.

Each 7nm CCD measures ~74mm² and has 3.9 billion transistors, while the 12nm IOD is ~125mm² and has 2.09 billion transistors. That means the 3900X comes with ~273mm² of silicon that sports ~9.89 billion transistors.

The 3900X's larger cache comes courtesy of the denser 7nm manufacturing process, but it does have a slightly higher latency (on the order of "five or six" clocks) than the 16MB of L3 cache found on previous-generation models. However, the increased capacity allows the processor to store more data closer to the execution cores, thus increasing cache hit rates that ultimately yield more performance. AMD also decreased the size of its L1 instruction cache from 64KB with the first-gen Zen processors to 32KB for Zen 2 chips. This allowed the company to expand its microop cache, and paired with changing the L1 instruction cache from 4-way to 8-way associativity, AMD feels this provides a more balanced approach to its cache subsystem. 

The -9900K's 16MB of L3 cache pales in comparison from a capacity standpoint, but cache bandwidth and latency are more important metrics. We'll put hard numbers behind the differences on the following pages.

As a sidenote, AMD now calls its combined L2+L3 cache "GameCache" to highlight to casual consumers the importance of cache to gaming performance, but we'll stick with the established terms.

Ryzen 7 3700X

The eight-core 16-thread Ryzen 7 3700X slots in at $329 and comes with a 65W TDP rating, which is significantly lower than the competing Core i7-9700K's 95W rating. You'll notice that AMD has maintained similar price points for the new models compared to the previous-gen Ryzen 7's, but we caution that pricing is a moving target for the last-gen chips.

Although third-gen Ryzen pricing is close to the current-gen processors on sale, this is far lower than the per-core pricing at the launch of the previous gen. Normalize the numbers to price-per-thread, and its clear AMD maintains a pricing advantage over Intel's lineup. But performance varies based on architecture, so the price-to-performance ratio is where the rubber meets the road.

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The Ryzen 7 3700X features a single CCD with all eight active cores connected to the I/O die, highlighting that the company's Zen 2 architecture is inherently scalable. Threadripper processors also come with varying numbers of compute dies, but substitute in 'dummy' dies to ensure structural rigidity and prevent crushing the integrated heat spreader (IHS) when you tighten down your cooler. The smaller surface area of the 2700X's IHS doesn't require a dummy die, so this pad is simply left unoccupied.

AMD hasn't sampled the Ryzen 7 3800X yet, which features a higher 105W rating and 3.9 / 4.5 GHz base/boost clocks, which is higher than the Ryzen 7 3700X's 3.6 / 4.4 GHz base/boost frequency. It also looks like a compelling part, so look to these pages for a review soon. 

Both the Ryzen 9 3900X and the Ryzen 7 3700X come with the bundled Wraith Prism RGB cooler that features four direct-contact copper heat pipes, three independent RGB zones, switchable fan profiles, and a 39 dB(A) noise rating. The cooler is rated to dissipate 116W of waste heat in "L" mode (2800 RPM) and 124W in "H" mode (3600 RPM). Cooler Master manufactures the heat sink/fan, while AMD provides software for controlling the lighting and fan profiles. Company representatives claim the cooler represents a roughly $43 value, and that it also allows for some overclocking headroom. Intel's K-series models, in contrast, don't come with a bundled cooler.

Memory Subsystem and Overclocking, Infinity Fabric

Ryzen 3000 chips support dual-channel DDR4-3200, a step up from the previous-gen's support for DDR4-2966. That should boost performance significantly because the Zen 2 microarchitecture, like its predecessor, benefits heavily from increased memory performance (particularly in gaming).

AMD's new Zen 2 microarchitecture uses a centralized memory controller on the I/O die, which helps ensure consistent memory latency in the multi-die Ryzen 9 models. It also improves cache access latency. AMD has also overhauled the Infinity Fabric, doubling its throughput by increasing the previous-gen 256-bit interconnect to 512-bit, which facilitates access to memory and enables the PCIe 4.0 interface. AMD also instituted more fine-grained Infinity Fabric quality of service controls and claims to have reduced the amount of energy required to transfer a bit by 27%. 

AMD has improved memory overclocking substantially, partly due to decoupling the Infinity Fabric from the memory clock. AMD's first-gen Ryzen processors had plenty of difficulties with memory overclocking when they first launched, but AMD has addressed those concerns with the second-gen products and has even demoed an air-cooled Ryzen platform running at DDR4-5100. We also didn't encounter any issues during our testing.

As with previous-gen Ryzen, memory overclocking confers big performance speedups for gaming. To sidestep the Infinity Fabric's maximum frequency of 2,000 MHz, which effectively constrains memory overclocking, AMD allows users to separate the memory and Infinity Fabric clock dependencies. The domains remain tied together at a 1:1 ratio up to DDR4-3600, but run at a 2:1 ratio beyond that transfer rate. This setting, which is also user-adjustable in the BIOS, improves memory bandwidth but comes with a latency penalty (~9ns). Tuners can also adjust the Infinity Fabric clock (fclk) in 33Mhz increments to get an extra kicker during overclocking. AMD says that the price/performance sweetspot will be around DDR4-3600.

As before, AMD supports up to 128GB of RAM and enables ECC support, but AMD leaves qualification and enablement of the feature up to motherboard vendors.

As seen with the first-gen Zen chips, AMD's official supported memory data transfer rates vary based on the type of DIMM (single rank or dual rank) and the number of populated channels, as outlined above.

PCIe 4.0 Comes to the Desktop

Ryzen 3000 processors support the PCIe interface on X570 motherboards, and while the chips will drop into some previous-gen AM4 motherboards, the processor will downshift into PCIe 3.0 on those platforms. AMD has also infused the new technology into its "Navi" Radeon 5000 series GPUs and worked with storage vendors to assure a supply of speedy new PCIe 4.0 SSDs. We recently had the opportunity to take an early look at PCIe 4.0 SSD performance, which you can see here.

PCIe 4.0 provides yet another advantage for performance seekers, particularly in the content creation realm, over Intel's platform, but it doesn't materially impact gaming performance (at least not yet). The new interface also comes at the cost of higher pricing for X570-equipped motherboards due to tighter signalling requirements. Those prices could recede over time as the pricing of the PCIe 4.0 component ecosystem, like switches and redrivers, benefit from economies of scale, but AMD has wisely encouraged its partners to continue offering the current-gen X470 motherboards that will now serve as a lower tier of motherboards.

AMD's new Ryzen 3000 series lineup is fully compatible with existing X470 motherboards and will operate at their full performance on the previous-gen boards, albeit at the loss of PCIe 4.0 connectivity. That shouldn't be too much of a concern for users without PCIe 4.0 devices or SSD RAID storage arrays that hang off the chipset. Fast storage arrays will certainly benefit from the faster PCIe 4.0 connection between the chipset and processor, though. 

Ryzen-Specific Windows 10 Scheduler Updates

AMD worked with Microsoft to deliver on a much needed feature: A Ryzen-aware scheduler. The new scheduler arrived with the Windows 10 May update and benefits both current-gen and previous-gen Ryzen models (Threadripper and Ryzen 3000 processors).

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The new scheduler pins threads within a single CCX (the four-core clusters inside each CCD) before scheduling threads to other CCXes. This approach reduces latency during thread synchronizations or frequent cache accesses, thus improving performance for all existing Ryzen processors. AMD says the feature doesn't benefit all applications, but can result in significant performance improvements in those that do.

AMD also introduced its Collaborative Power Performance Control 2 (CPPC2) feature, which is a software feature that manipulates Ryzen 3000's power states from within the operating system. This is similar to Intel's Speed Shift technology and reduces power state transition latency from 30ns to 1ns, which ultimately saves power and boosts efficiency. The feature comes enabled in the latest AMD chipset drivers and the Windows 10 May update (and newer).

As before, these mainstream models don't come with integrated graphics, meaning you'll need a discrete GPU.

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