AMD Ryzen 5900X vs 3900X

We compare the new Zen 3 AMD Ryzen 5900X to the AMD Ryzen 3900X Zen 2 CPU to see which is better


Update: Check out our Where to Buy pages to get your hands on these AMD CPUs:

With the latest 5000 series of CPUs, AMD are aiming firmly at knocking Intel off the top spot for the coveted title of Best Gaming CPU. Their main contender in this fight, excluding the more expensive 5950X which is also aimed at creatives and work station users, is the 5900X. The 3900X was the previous generation’s version of a CPU at this price point, but didn’t manage to beat Intel’s competing effort of the i9-10900K in single-core speed (the crucial factor in gaming), nor did it have the chops to get the most out of a rig running an RTX 3090 GPU. So, let’s see whether AMD’s latest offering can meet their claims and whether it’s worth the extra cash over the older and cheaper 3900X.

Zen 2 vs Zen 3 Architecture

“Zen” is the designation used by AMD for the different generations of their CPU architecture since 2017. The 3900X is created using Zen 2 architecture and the 5900X is based on the new Zen 3. Despite both Zen 2 and Zen 3 being based on a 7nm process, AMD have refined the technology substantially for Zen 3, increasing the power efficiency and most crucially the IPC (Instructions Per Clock) of the same size process. We can expect next year’s Zen 4 to have these same improvements incorporated but on the smaller 5nm process.

It seems that most of the performance increases in the new Zen 3 are due to changes AMD has made in the cache layout. Instead of two lots of 16MB L3 memory with four CPU cores between them, AMD are now able to give eight CPU cores simultaneous access to one large 32MB L3 memory cache. With these improvements, any of the cores can now directly access data stored in the single large memory pool (e.g. those concerning the physics of persistent objects within a game world), rather than the information having to move across the ‘Infinity fabric’ in between the separate cache segments. So in effect, the 3900X has 4x16MB cache sections, with four assigned cores (eight threads) each whereas the 5900x has 2x32MB cache sections, with eight assigned cores (16 threads) each – the same amount of memory and cores overall, just better utilized. All-in-all this means a greater speed of process resulting in less latency for games.

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Workstation Performance

Unlike the $250 more expensive 5950X, which is targeted towards creatives and professionals who need a desktop PC that can perform workstation tasks as well as game the 5900X, and its 3900X predecessor, are aimed purely at enthusiast-level gamers. This is not to say that you won’t be able to get some multi-core productivity out of the CPU in these tasks. As the below benchmarking shows, the rendering speed and multicore performance for the new 5900X still competes very favorably, surprisingly even outperforming the older 3950X, previously the industry favorite for small to medium-sized creative professionals and hobbyists, in certain areas. Overall though the 3950X still has the edge in workstation use as you would expect from its greater number of cores and threads. 

If you are looking to build a proper workstation rig, then we would recommend looking at the 16 core 5950X or alternatively, if you are constrained by a tight budget, consider a second hand 3950X. Exceptions to this would be if you are only interested in performance on software like Adobe Photoshop, which is mostly reliant on single-core speed than multi-core usage. For the vast majority of other editing and visual effects software, as well as streaming usage, the 5950X is your best bet. Nevertheless, when comparing the 5900X vs the 3900X for workstation use, the 5900X definitely comes out on top.

Ryzen Cinebench R20

Gaming Performance

At first glance, you might notice that the 5900X actually has a slightly lower base clock speed than the 3900X. Although this may seem initially counterintuitive, the clock speed is only part of the story with performance, the aforementioned improvements in architecture mean the number of Instructions Per Clock (IPC) is significantly greater for the 5900X, so the overall number of instructions the CPU is capable of over any given time is higher. 

Whilst newer games are beginning to utilize multi-processor power and this trend is likely to increase, the big metric when it comes to gaming is still single-core performance. Single-core (and even more so thread) performance is also the main consideration on certain applications like Adobe Photoshop. AMD’s aim with the 5900X was to create a CPU that could perform in both multi-core heavy tasks like the 3900X but also have the single-core power for gaming, in theory then the newer model should outperform the Zen 2 processor in this area by some margin.

In their original reveal presentation, AMD claimed an overall increase in performance between Zen 2 and 3 of around 19%. Let’s take a look at the latest benchmarks to see how true this is.

Ryzen Counter Strike Global Offensive
Ryzen Microsoft Flight Simulator 2020
Ryzen Shadow of the Tomb Raider

As is evident from the above FPS results, it seems like AMD’s claims were bang on the money, in fact, between the 3900XT and the 5900XT, on the games tested so far at least, the performance increase has if anything been understated. Shadow Of The Tomb Raider showed an average FPS increase of 25%, Microsoft Flight Simulator (a known CPU heavy game) an uplift of 22%, and CS:GO a very impressive 30%. Given the price difference between the two processors (assuming the 3900X remains at $464) of 18%, it seems to us like the 5900X represents great value. This is especially true if you are considering purchasing a new Radeon 6000 series graphics card, as we will go over below.


AMD Ryzen 5000 CPUs With Radeon 6000 GPUs – Smart Access Memory

The final thing to consider when comparing the 3900X and the 5900X is whether or not you are intending to buy one of the new Radeon 6000 series graphics cards from AMD. As discussed here, in more detail, the Smart Access Memory feature allows 5000 series Ryzen CPUs to gain additional performance through more efficient usage of GPU memory, ranging from between 2% – 13% additional FPS performance on the games AMD showed us. Once the new Radeon graphics cards are released then we will have a better idea of how realistic this is, but so far AMD’s other performance claims have proved genuine. 

Bear in mind that the FPS gains between the 5900X and the 3900X shown in the above benchmark charts do not factor in Smart Access memory, so essentially it means additional free performance if you are planning on buying a Radeon card anyway. Indeed anyone likely to buy an AMD 6000 series GPU really would be missing out if they paired this with a new 3900X CPU – in this situation the 5900X would be the obvious choice.

amd smart access memory and rage mode

In Summary

In all aspects of performance, the 5900X is the superior CPU to the 3900X. For £85 more, based on current prices, you get approximately 20%-25% uplift in gaming performance, sometimes more depending on the game, as well as large improvements in workstation usage. If you are buying new then the 5900X is the obvious choice, and if you are buying a Radeon 6000 series graphics card as well then the decision becomes even more of a no brainer, though if second-hand prices come down substantially for the 3900X and you are working on a tight budget, this may also be worth considering.

If you already own a 3900X then the question is, is $549 worth an approximately 20%-25% uplift in FPS performance to you (excluding any additional bonuses from Smart Access Memory)? Selling your current 3900X on the second-hand market could of course reduce the net impact on your wallet, and if you’re buying a new Radeon 6000 series graphics card then the additional SAM performance and futureproofing the new cards offer further sweetens the deal.

All-in-all, the 5900X is a significantly superior CPU to its predecessor, and this is one instance where we think the generational uplift is definitely worth the money.