AMD Radeon RX 6600 XT PCI-Express Scaling 66

AMD Radeon RX 6600 XT PCI-Express Scaling

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Introduction

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In this article, we'll try to understand the performance impact of various PCI-Express configurations for the AMD Radeon RX 6600 XT graphics card. We've been doing PCIe scaling articles for well over a decade: RTX 3080, RX 5700 XT, RTX 2080 Ti, GTX 1080, R9 Fury X, GTX 980, GTX 480, and HD 7870. This kind of article is usually reserved for the topmost-tiered GPUs from AMD and NVIDIA, making this the first time we're evaluating a mid-range GPU from this perspective.

The basis for this article is the fact that the RX 6600 XT, and 7 nm "Navi 23" silicon it's based on, physically only features a PCI-Express 4.0 x8 bus interface. The GPU only has pins for eight PCIe lanes. This was probably a design choice made to cut costs and save pin-count on the compact GPU package. A smaller PCB footprint also makes the GPU desirable for notebook designers looking to hardwire the package directly onto the mainboard, as is the norm these days.



PCI-Express 4.0 x8 is a huge amount of bandwidth. Given that PCIe Gen 4 pushes 16 Gbps per direction, you're looking at 16 GB/s per direction; or at bandwidth that's identical to PCI-Express 3.0 x16. This should be plenty for a mid-range GPU like the RX 6600 XT, end of the story? But wait...there's a catch. When installed on older platforms with PCIe Gen 3, such as Intel 10th Gen "Comet Lake" (or older), or AMD Ryzen 2000 series (or older), the GPU is forced to operate at PCI-Express 3.0 x8, which is half the bandwidth of Gen 4 x8. And if you're on even older platforms, such as AMD FX, however unlikely, it's going to run at PCI-Express 2.0 x8, which is about a quarter of the bandwidth of Gen 4 x8.



The Radeon RX 6600 XT isn't the first time AMD designed a mid-range GPU with x8 PCIe, the RX 5500 XT from the previous RDNA generation also uses PCI-Express 4.0 x8. We didn't much care about this topic back then because those were happier times, when gamers were spoiled for choice with GPUs. In today's unfortunate environment for PC component shoppers, the RX 6600 XT and GeForce RTX 3060 are important parts, as even with scalper pricing, they can be had for around $600, which is somewhat "affordable" to gamers. Among the two, the RX 6600 XT emerged the performance king of the mid-range segment, and so here we are.

In this review, we will test the Radeon RX 6600 XT on various PCI-Express configurations that include native PCI-Express 4.0 x8, PCI-Express 3.0 x8, PCI-Express 2.0 x8, and PCI-Express 1.1 x8. With each older generation, we're effectively halving the bus bandwidth. We switch to the older PCIe generations using the motherboard's UEFI Setup program, and verify with GPU-Z.

Test System

Test System - VGA 2021.1
Processor:AMD Ryzen 7 5800X @ 4.8 GHz
(Zen 3, 32 MB Cache)
Motherboard:MSI B550-A Pro
BIOS 7C56vA5 / AGESA 1.2.0.0
Resizable BAR:Enabled on all AMD RDNA2 & NVIDIA Ampere cards
Memory:Thermaltake TOUGHRAM, 16 GB DDR4
@ 4000 MHz 19-23-23-42 1T
Infinity Fabric @ 2000 MHz (1:1)
Cooling:Cooler Master MasterLiquid ML240L V2
240 mm AIO
Storage:2x Neo Forza NFP065 2 TB M.2 NVMe SSD
Power Supply:Seasonic Prime Ultra Titanium 850 W
Case:darkFlash DLZ31 Mesh
Operating System:Windows 10 Professional 64-bit
Version 20H2 (October 2020 Update)
Drivers: RX 6600 XT: 21.8.1 Beta
RTX 3070 Ti: 466.61 Beta
RTX 3080 Ti: 466.54 Beta
RTX 3060, 3060 Ti, 3070, 3080, 3090: 466.27 WHQL
RX 6700 XT, 6800, 6800 XT, 6900 XT: 21.4.1 WHQL
All other AMD: 21.2.3 Beta
All other NVIDIA: 461.72 WHQL
Benchmark scores in other reviews are only comparable when this exact same configuration is used.

  • All games and cards are tested with the drivers listed above—no performance results were recycled between test systems. Only this exact system with exactly the same configuration is used.
  • All graphics cards are tested using the same game version.
  • All games are set to their highest quality setting unless indicated otherwise.
  • AA and AF are applied via in-game settings, not via the driver's control panel.
  • Before starting measurements, we heat up the card for each test to ensure a steady state is tested. This ensures that the card won't boost to unrealistically high clocks for only a few seconds until it heats up, as that doesn't represent prolonged gameplay.
Each game is tested at these screen resolutions:
  • 1920x1080: Most popular monitor resolution.
  • 2560x1440: Intermediary resolution between Full HD and 4K, with reasonable performance requirements.
  • 3840x2160: 4K Ultra HD resolution, available on the latest high-end monitors.

Assassin's Creed Valhalla


Released: 2020 — API: DirectX 12 — Engine: AnvilNext 2.0

It is the year 873 AD, the most violent period in Norwegian history. A Viking clan leader takes a group of refugee warriors across the seas to medieval England, where they set up camp as barely welcome migrants to the local kingdoms. You form alliances with local lords and raid Saxon strongholds for resources to build and grow your settlement. The historic cities of Winchester, London, and York, as well as vast landscapes of Norway, are brought to life in this outstanding Assassin's Creed experience.

Based on the same AnvilNext 2 engine that powers other Ubisoft titles, Assassin's Creed Valhalla takes advantage of DirectX 12 and offers outstanding visuals that look amazing even without raytracing. We tested at the highest details using our own custom test scene.

Battlefield V

Battlefield V

Released: 2018 — API: DirectX 11 — Engine: Frostbite

Battlefield V is the latest chapter in EA's smash-hit online multiplayer shooter franchise. The series has come full circle since its debut "1942" and is set in World War II. The single-player campaign is broken up into bite-sized chunks called War Stories. Much like Battlefield 1, each depicts a different theater of war, a different protagonist, and a different mission. The multi-player builds on the franchise's core strengths with the addition of new game modes and room for a future mode rivaling battle royale.

Based on the Frostbite 3 engine by EA-DICE, Battlefield V supports both DirectX 11 and DirectX 12, and newer technologies such as DirectX Raytracing. In this particular test, we used DirectX 11 as that's the API used by the majority of players.

Battlefield V FPS 1920x1080
Battlefield V FPS 2560x1440
Battlefield V FPS 3840x2160
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May 23rd, 2022 02:06 EDT change timezone

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