AMD Radeon RX 6800 XT and RX 6800 | Review
Technical specifications
Let's start by talking about technical specifications. The new Radeon RX 6800 XT and RX 6800 are based on the new RDNA 2 architecture, which introduces several innovations compared to the previous RDNA. Before talking in more detail about the new architecture, let's see what the other features of the two GPUs are.For the new Radeon RX 6000 AMD has abandoned the typical blower design, opting for a more classic open air with three fans that it guarantees lower temperatures and greater silence. The Radeon RX 6800 XT and RX 6800 are virtually identical aesthetically, they are powered by a dual 8-pin connector and both measure 267 x 120mm. The difference lies in the thickness of the card: the first occupies 2.5 slots, while the second is a classic 2 slot.
Among the novelties we also find support for HDMI 2.1 VRR, there is also a USB port -C which supports both VR viewers and monitors that take advantage of this connection.
Radeon RX 6800 XT Radeon RX 6800 Radeon RX 5700 XT Architecture RDNA 2 RDNA 2 RDNA Production process 7 nm 7 nm 7 nm Transistor 26.8 billion 26.8 billion 10.3 billion Die size 519 mm² 519 mm² 251 mm² Compute Unit (CU) 72 60 40 Ray Accelerator 72 60 - Stream Processor 4608 3840 2560 Frequency (game / boost) 2015/2250 MHz 1815/2105 MHz 1755/1905 MHz ROPS 128 96 64 AMD Infinity Cache 128 MB 128 MB - Memory 16GB GDDR6 16GB GDDR6 8GB GDDR6 Memory bandwidth 512 GB / s 512 GB / s 448 GB / s Memory interface 256-bit 256-bit 256-bit TBP 300 W 250 W 225 W Compared to the previous top of the range, the Radeon RX 5700 XT, the new Radeon RX 6800 XT and RX 6800 offer more Stream Processors, more video memory and higher frequencies, which result in a higher TGP. Compared to the RTX 3080 the new Radeon RX 6800 XT offers more memory, but of the type GDDR6 and not GDDR6X. Frequencies are also higher, with a maximum boost reaching 2250MHz versus 1710MHz on the RTX 3080, while TBP is lower (300W versus 320W).
Similarly, the Radeon RX 6800 offers double the video memory of the RTX 3070, but in both cases here we find some GDDR6. Again, the frequencies are higher on the Radeon, which reached 2105MHz against the 1730MHz of the RTX 3070, while the TGP is higher and equal to 250W, against the 220W of the Nvidia GPU.
RDNA 2 novelties
The biggest novelty of the new Radeon RX 6800 XT and RX 6800 is undoubtedly the RDNA 2 architecture, which as one might expect brings with it several novelties. One of the most interesting is AMD Infinity Cache, a cache memory present on the die that allows extremely fast access to data and acts as a bandwidth amplifier, allowing you to achieve high performance while maintaining excellent energy efficiency. The 128MB of cache memory allows to improve the bandwidth by 3.25 times and the bandwidth / watt efficiency by 2.4 times.Another new feature of RDNA 2 is support for DirectX 12 Ultimate, which is declined in the ability to manage DirectX Ray Tracing, Variable Rate Shading (VRS), mesh shader and sampler feedback.
Ray Tracing is managed by dedicated units called Ray Accelerators. Each Ray Accelerator is able to calculate up to four radius / box intersections or a radius / triangle intersection for each clock cycle; once all the intersections of the rays have been calculated with the geometry of a scene according to a hierarchy of limit volumes (BVH), it reorders them and returns the information to the shaders.
The Variable Rate Shading is a function that allows the hardware to focus more on rendering the main points, in order to offer the best image quality only in the most important areas of a scene. Support in RDNA 2 is built on all pixel pipes and allows developers to choose between three different shading rates: 1 × 1, 2 × 1 and 1 × 2. The AMD implementation also allows you to choose the shading rate for each region large 8 × 8 pixels, guaranteeing developers great flexibility and the ability to take care of even the smallest detail.
Another novelty is the Radeon Media Engine , Which offers new hardware encoding and decoding capabilities. The new Radeon RX 6800 allow to encode and decode both H.264 and H.265, moreover they support the decoding of AV1 and VP9.
VP9 H.264 H.265 AV1 Decoding 4K90 / 8K24 1080p600 / 4K150 1080p360 / 4K90 / 8K24 8K30 Encoding - 1080p360 / 4K90 1080p360 / 4K60 -
AMD Smart Access Memory: what is it?
Among the novelties of the new Radeon RX 6000 there is also Smart Access Memory (SAM), a technology that guarantees higher performance by allocating more space for the GPU memory.Usually, the processor can only access a small part of the GPU's VRAM. This amount is defined by the PCIe Base Address Register (BAR) and amounts to 256MB, which is too small and inevitably creates a bottleneck, degrading performance. By exploiting the Resizable BAR technology present in the drivers it is possible to renegotiate (and expand) the allocated space, increasing it; SAM does just that, allowing the CPU to access all available video memory, effectively removing the bottleneck and increasing performance.
Smart Access Memory technology has quite stringent requirements for now: you'll have to be in possession of a Radeon RX 6000 video card, a Ryzen 5000 processor and a motherboard with a 500 chipset. To enable it you will also need to have a suitable BIOS on your motherboard, which allows you to activate the "Above 4G Decoding" and " Resizable BAR Support ”.
