On the stage in Hawaii last year, amidst the unveiling of the AMD Radeon™ R9 and R7 Series, we mentioned that our GPUs would be ready to support a new generation of UltraHD displays with so-called SST scalers. SST, or single stream transport, promised to make the configuration of 4K monitors easier by eliminating the need for stitching two halves of a display together in software – a staple of first-generation 4K displays. As of late, SST monitors have begun to appear in the market, and we wanted to take some time to talk about their benefits and performance on AMD Radeon™ graphics cards.
SINGLE-STREAM TRANSPORT (SST) vs. MULTI-STREAM TRANSPORT (MST)
When physical LCD panels capable of displaying 3840x2160 content hit the market, the underlying circuitry used to put content on the LCD wasn’t quite as advanced. Part of that circuitry is a critical component known as the “scaler,” which permits the monitor to render pictures at the LCD panel’s native resolution, or at a resolution chosen by the user. Not all monitors have scalers, but many do, especially 4K displays.
The scalers in first-generation 4K panels had a peak resolution of 1920x2160, which is exactly half the resolution of a 4K LCD. At a typical gaming refresh rate of 60 Hz, these scalers simply did not offer enough bandwidth to display a 3840x2160 image 60 times per second.
To address a 4K panel’s full resolution at 60 Hz, two scalers were used simultaneously. Each scaler powered half (1920x2160) of the LCD at 60 Hz, and the signals from these scalers were interleaved within a single DisplayPort™ cable, where an AMD Radeon graphics card would interpret the signal as two separate “tiles” that could be automatically stitched together into a single large surface (figure 2).
The technology to carry a signal for two or more monitors on a single cable is called MST, or “multi-stream transport,” a component of the DisplayPort 1.2 specification long supported by AMD Radeon graphics cards. MST is the same feature that has also allowed AMD Radeon GPUs to support multiple monitors from a single DisplayPort output via hubs or daisychaining for many years.1
While MST was a smart and effective solution to bring 4K panels to market at 60 Hz, the graphics industry was already hard at work to realize an ecosystem of support for UltraHD via SST, or “single-stream transport.” These new-generation scalers would have the bandwidth to drive a full 3840x2160 at 60 Hz as a single tile over DisplayPort, which would simplify configuration for the user and help reduce production costs and complexity for the manufacturer.
SUPPORTING 4K60 SST DISPLAYS
Monitors like the Samsung U28D590D (now available) and the upcoming Asus PB287Q are the first of many relatively affordable UltraHD monitors to feature scalers that support 3840x2160 at 60 Hz via SST. Supporting these displays in software, such as with the AMD Catalyst™ graphics driver, is not a trivial matter.
To date, gaming monitors have rarely (if ever) presented such a large rendering surface to the graphics driver. In fact, 2560x1600 monitors presented the largest contiguous block of pixels that would commonly be encountered by a gaming GPU. Every other display configuration, such as a tiled UltraHD display, or an AMD Eyefinity technology configuration, was a larger surface stitched together from many smaller surfaces. Programmatically speaking, all of these are distinct scenarios that must be accounted for with unique code.
Developing that unique code for these new 4K60 SST panels requires a close relationship with the scaler vendors driving these panels. In the case of the in-market Samsung U28D590D, the scaler vendor and AMD worked very closely with prototypical monitors to ensure that AMD Radeon™ graphics cards would be ready to support Samsung’s display when it debuted. More broadly, we are working with all top scaler vendors to ensure our Hawaiian promise that AMD Radeon™ graphics cards will always be the gold standard for UltraHD readiness.
BENCHMARKING SST 4K60
While individual graphics cards like the AMD Radeon™ R9 290X have architectural optimizations to support 4K resolutions, many gamers understandably turn to multi-GPU configurations (e.g. AMD CrossFire™ technology) to squeeze the most performance out of their shiny new UltraHD setup.
In the below performance comparison (figure 3) between the AMD Radeon™ R9 295X2 and SLI GeForce GTX 780 Ti, the benefit of AMD’s robust relationships within the display industry is clear: AMD Catalyst™ is ready to support high-performance gaming experiences on 4K60 SST displays, but our competition clearly has more work to do.
THE GOLD STANDARD FOR ULTRAHD
With a rich history of pioneering new and exciting ways to game on large or multiple displays, we have spent months leveraging that expertise with a number of innovations that have established us as the undisputed leader in UltraHD gaming:
- We were the first to equip a graphics card with 64 ROPs to drive the pixel rate demanded of UltraHD displays.
- We were first to enable gamers with the ability to stitch tiled 4K displays together via AMD Eyefinity technology.
- We were the first to automatically stitch those tiles together with the industry standard Tiled Display Topology Data Block specification.
- We were the first to release a single graphics card widely acclaimed for its unprecedented UltraHD performance: the AMD Radeon™ R9 295X2.
And now we are first to market with fully-functional, day-one support for the latest and greatest UltraHD panels with 60 Hz SST scalers. If nothing else, this represents our commitment to serve you – our loyal and enthusiastic customers – with healthy engineering efforts to comprehensively support state-of-the-art gaming experiences.
(We’re gamers too. My cubicle neighbor would revolt if it didn’t work right. Frag on!)
Robert Hallock does Technical Communications for Desktop Graphics at AMD. His postings are his own opinions and may not represent AMD’s positions, strategies or opinions. Links to third party sites, and references to third party trademarks, are provided for convenience and illustrative purposes only. Unless explicitly stated, AMD is not responsible for the contents of such links, and no third party endorsement of AMD or any of its products is implied.
1. AMD Eyefinity technology supports up to six DisplayPort™ monitors on an enabled graphics card. Supported display quantity, type and resolution vary by model and board design; confirm specifications with manufacturer before purchase. To enable more than two displays, or multiple displays from a single output, additional hardware such as DisplayPort-ready monitors or DisplayPort 1.2 MST-enabled hubs may be required. Maximum two active adapters supported. See www.amd.com/eyefinityfaq for full details.