AMD Zen 3 reviewed: The best CPUs to buy in 2021 (Part I)- Technology News

Anirudh RegidiAug 12, 2021 14:46:12 IST

2020-21 has been an interesting period for PCs. A pandemic-fueled spike in demand coupled with a severe parts shortage means that supply just couldn’t keep up with demand. Prices have been all over the place and parts are rarely in stock. As such, getting our hands on AMD’s new, Zen 3 based Ryzen 5000 chips has proven to be a challenge.

Now, 6 months after the launch of the chips, things are finally looking up and we’re seeing CPUs and GPUs on store shelves. If you, like myself, have been holding off on an upgrade for several years now, it’s a good time to look at where things stand and yet again mull over that long overdue upgrade.

So… which CPUs should we be buying in 2021?

AMD vs Intel: Design

Before we dive in, it’s worth looking at how AMD and Intel have approached CPU design. This will help us understand the strengths and weaknesses of the chips, and inform our purchase decision.

If you’d like to skip straight to the data, head to part II of the review here.

If we think of a CPU as a factory, where data (raw material) is processed into a finished product, Intel’s approach is akin to Tesla’s Gigafactory where everything happens under one roof, and AMD’s to a more distributed approach involving smaller factories (called Core CompleX or CCX) and a complex system for communication (that AMD calls Infinity Fabric) between these mini factories. Zen 3 also introduced “chiplets”, where each component (Like the CCX) can be manufactured separately.

Intel’s monolithic architecture means that a CPU is essentially designed and manufactured as a single unit. This is great for efficiency and performance, since everything operates at the same frequency — so to speak — but the design is difficult to scale up and expensive to manufacture. A flaw in a single transistor could ruin an entire chip. Whether you’re buying a quad-core Intel CPU or a 10-core one, the entire CPU is, for all intents and purposes, functioning as a single unit.

AMD’s distributed approach, on the other hand, splits the CPU into two primary components: the CCX and IO dies. The CCX is a 6-core or 8-core unit that handles processing, while the IO die handles communication between the CPU and the rest of the components (RAM, storage, GPU, etc.). AMD’s Infinity Fabric handles internal communication between the CCXs and the IO die.

This design not only allows AMD to mix and match these CCXs as required, but it also allows AMD to scale up the design with relative ease and offer more cores at a relatively low cost. AMD could simply add more CCXs to the design and build 6 (1x 6-core CCX), 8 (1x 8-core CCX), 12 (2x 6-core CCX), 32 (4x 8-core CCX) CPUs with relatively minor modifications to the design. Do note that Zen 3 currently tops out at 16 cores, but previous designs did hit 64-core cores.

The downside to this approach is, of course, the difficulty in keeping these discrete modules in sync. Teething issues and developer support aside, this challenge played a significant role in keeping AMD’s earlier architectures — Zen and Zen+ — from offering real competition to Intel in 2017 and 2018. Their biggest achievement, I think, was forcing Intel to reduce prices and double the core counts in its CPUs.

Zen 2 vs Zen 3, and Intel’s response

Zen 2, which arrived in 2019, was a big upgrade, introducing chiplets, a 2^nd Gen Infinity Fabric that was far more efficient, a larger cache (think of it like RAM, but on a CPU), a 7 nm manufacturing process, and support for PCIe Gen 4 (doubling bandwidth to GPUs and PCIe-based storage).

Chiplets are small chips that can be manufactured separately and integrated into a larger die. This, again, brings down the cost of manufacturing a CPU because yields are higher — a smaller chip has fewer points of failure.

Intel’s response was, for lack of a better phrase, a hot mess. Intel’s 10th Gen Core architecture called Comet Lake was fast, beating Zen 2 on the gaming front, but could only do so while running incredibly hot and consuming a tremendous amount of power. The Intel Core i9 10900K I tested in 2020, which was rated at 125 W TDP (Thermal Design Power, an indicator of the heat that needs to be dissipated by your CPU cooler), easily hit 300 W when pushed to the limit. My 240 mm liquid cooling loop could barely keep temperatures in check and operating at 90-95°C with fans screaming was… normal. I ran a 16-core 5950x on the same cooler with zero issues and minimal noise.

To add to this, Comet Lake lacked support for PCIe Gen 4, and was based on a heavily modified 6th Gen microarchitecture and venerable 14 nm manufacturing process that debuted in 2015.

While Comet Lake was the first of Intel’s chips to be competitively priced, any cost savings were offset by the need for expensive motherboards (for overclocking and faster RAM support) and cooling solutions to allow these chips to perform.

AMD was nipping at Intel’s heels, and Zen 2 was already proving to be very good value.

Then, mere months later, came Zen 3.

Zen 3: An overview

The name indicates that Zen 3 is a new architecture, and while that may be true, diving deep into the spec sheets and design documents for Zen 3 suggests that it’s more a redesign of Zen 2 — where each component was examined and re-engineered — than an entirely new architecture.

The biggest update here is to the CCX, which now goes up to 8-cores per CCX from the previous 4-core design. Previous gen 6- and 8-core CPUs used 2x 3-core CCXs and 2x 4-core CCXs respectively. Each Zen 3 CCX also gets up to 32 MB of L3 cache (an extremely fast data buffer), which is up from 16 MB on the previous gen.

Speaking of, here’s the full list of Zen 3 desktop CPUs currently available to consumers. Variations of these CPUs are currently available to OEMs, but not for retail purchase:

The base frequencies are what you’ll get at base TDP and will scale up based on your cooling solution. With my setup, these CPUs generally hit around 4.5 GHz on all cores under full load, with only the 5950x struggling to cross the 4 GHz mark. Given the number of cores it’s packing, this is understandable.

Another thing to note is that Intel’s CPUs easily cross the 5 GHz mark under light, single-threaded loads like gaming, and I’ve personally pushed the Intel 10700K and 10900K to an all-core turbo of 5.1 and 4.9 GHz respectively with minimal effort. This is primarily where Intel’s strength lies.

In effect, AMD claims that Zen 3 shows a 19 percent IPC improvement compared to Zen 2.

Neither of these CPUs has an integrated GPU.

11^th Gen Intel (Rocket Lake) vs Zen 3

Intel’s response was… strange, to say the least.

We had high expectations from the Rocket Lake aka 11th Gen Intel Core architecture, but what we got instead was, well, a hack job. A hack job put together by some of the best engineers on the planet, but a hack job nonetheless.

Rocket Lake, Intel’s “2021” Core architecture, was essentially a 10 nm-based 2019 microarchitecture (designed for low-power laptops) back-ported to a 14 nm manufacturing process and infused with the GPU architecture from a 2020 CPU refresh. Yes, it’s exactly as confusing as it sounds.

But that’s not all. The 6- and 8-core CPUs are basically the same chip, with the 6-core ones having 2 cores disabled, and the quad-core 11th Gen i3 parts are actually just 10th Gen Comet Lake parts with some modifications.

You can’t just take something built for 10 nm and scale it up by 40 percent and expect things to work. The length of the processing pathways changes, latencies increase, voltages and power draw go up, heat increases, etc. The result, as expected, is a power-hungry chip that runs so hot that the flagship 11900K had to drop two cores, a significant increase in core-to-core latency, and a minuscule performance lead over Zen 3’s best in gaming.

The 8-core flagship is so bad, in fact, that it’s beaten by the previous gen 10-core 10900K in many workloads. Compared to the 12- and 16-core Zen 3 chips, Intel’s flagship pales.

I haven’t tested these 11th Gen Core desktop CPUs yet, so I’ll just summarize what dozens of reviewers online have reported:

• When it comes to high-end desktop CPUs, Intel’s kinda lost the plot. The high price, low core count, and the need for expensive cooling and motherboards means there’s very little value to be had here. The lower end of the spectrum comprising Core i5 parts is still decent, but only if you already have an expensive motherboard or don’t intend to overclock. Even then, an overclockable Zen 2 CPU or 10th Gen Intel CPU is usually a better bet.
• When it comes to gaming, only the 11700K and 11900K manage to beat the equivalent Zen 3 chips (5800x, 5900x, 5950x), but only by a small margin and, again, at a tremendous cost in terms of heat and power.

If you’re looking for a high-end desktop CPU in 2021, that only leaves you with Zen 3 aka Ryzen 5000.

In part II, we’ll put Zen 3 through its paces and take a closer look at its performance.