AMD Radeon R9-285 review

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PCIe Gen 3 - ZeroCore Power - 4K Video playback

PCIe Gen 3

All cards in the entire AMD Radeon R7 to R9 range are PCI Express Gen 3 compatible which provides a 2x faster transfer rate than the previous generation, this delivers capabilities for next generation extreme gaming solutions. So opposed to the current PCI Express slots which are at Gen 2, the PCI Express Gen 3 will have twice the available bandwidth and that is 32GB/s, improved efficiency and compatibility and as such it will offer better performance for current and next gen PCI Express cards. To make it even more understandable, going from PCIe Gen 2 to Gen 3 doubles the bandwidth available to the add-on cards installed, from 500MB/s per lane to 1GB/s per lane. So a Gen 3 PCI Express x16 slot is capable of offering 16GB/s (or 128Gbit/s) of bandwidth in each direction. That results in 32GB/sec bi-directional bandwidth. You do need a PCI-E 3.0 compatible motherboard and processor though. 

Power Consumption 

The R9 285 has a TDP of just over 190Watts, the R9 280X has a more steep rated peak TDP (maximum power draw) of 250 Watt, and last one really is quite a bit. AMD however focused on idle states as well, when you are in desktop mode for example in the year 2008 on 55nm a graphics card would draw up-to 90 Watt. That changed dramatically on the 40nm nodes and product towards a much better ~20 Watt. A new precedent was being set with the initial R7000 launch though as in desktop idle mode, the graphics cards only consume 2.7 Watt. So when the unutilized GPU is more than 95% it can almost shut 99% of itself down, even the ventilator will spin down and disable itself (which is a little freaky when you first see it really). So what's happening there you might ask ? Well, as soon as the system goes into long idle state and applications are not actively changing the screen contents, the GPU enters the ZeroCore power state. In the ZeroCore power state, the GPU core (including the 3D engine / compute units, multimedia and audio engines, displays, memory interfaces, etc.) is completely powered down. ZeroCore Power state maintains a very small bus control block to ensure that GPU content is still visible to the operating system and BIOS. The enablement of the ZeroCore Power feature is controlled by the driver. The driver on its end monitors the display contents and allows the GPU to enter the ZeroCore Power, in the condition that the GPU enters long idle and subsequent work requests are no longer being submitted to the engine. If any applications update the screen contents, ZeroCore Power technology can periodically wake the GPU to update the framebuffer contents and put the GPU back into the ZeroCore Power state. Furthermore, applications such as Windows 7/8 desktop gadgets are architected to minimize activity and save power in the long idle state. These applications are active during screen-on mode to display dynamic content such as weather, RSS feeds, stock symbols, system status, etc. but also have the intelligence to suspend any updates and activity when the system enters long idle. These applications will not wake the GPU from the ZeroCore Power state in long idle. I have immense respect for the new technology as it is a truly great achievement.

4K Video Playback

In 2011, AMD launched the Radeon HD 7900 Series, the first consumer discrete GPUs to support 4K output through HDMI and DisplayPort. During that time however, 4K content on a PC was limited to games since 4K video content was still rare and had not been widely adopted. In 2014, while 4K video is still not considered mainstream, content can be easily obtained. Increasing the pixel count from 1080p video by up to 4x subsequently increases the workload for decoding 4K (or UHD) content. The chart belows illustrates the amount of additional workload imposed on the CPU :

 

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The Radeon R9 285 is AMD’s first discrete GPU with a redesigned fixed-function decoder (UVD – Unified Video Decoder) that supports full hardware decode of 4K H.264 videos. This next generation UVD supports H.264 base, main and high profile, up to level 5.2. The chart below shows the benefit of having a fixed-function decoder :

 

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The primary benefit of having a fixed-function decoder, especially for high bit-rate 4K content, is the significantly reduced CPU utilization. This results in a more responsive system, lower battery life ( for mobile products ) and more importantly, the system will not exhibit any skipped frames during playback.

High Performance Transcoding

The AMD Radeon R9 285 also features a redesigned fixed-function encoder ( VCE - Video Coding Engine ) that supports full hardware encoding to H.264 format. This version of VCE supports encoding to H.264 baseline and main profiles. The main use case for VCE is transcoding, which is very useful when the user wants to save on storage space as well as allow older, lower power devices (such as handhelds, laptops, etc.) to decode and playback their content at lower resolutions and/or lower bit-rate. The VCE works in concert with the powerful UVD in the Radeon R9 285 to accelerate the transcoding pipeline. The chart below shows the performance uplift expected compared to the competition:

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