AMD Radeon HD 7770 and Radeon HD 7750

Anyone with a passing interest in PC graphics hardware knows that AMD released the high-end Radeon HD 7970 and HD 7950 GPUs recently, priced at around £450 and £350, respectively. Based on a new Graphics Core Next (GCN) architecture and providing solid performance with excellent power-draw characteristics, the asking price alone makes them aspirational products.

The initial 7000-series cards were designed to satisfy the needs of enthusiast users, but AMD is now shifting its focus to the mainstream with the introduction of two mid-range solutions; the Radeon HD 7770 and Radeon HD 7750.

Priced in the region of £125 and £90, respectively, the HD 7770 and HD 7750 are designed to bring the goodness of the GCN architecture to a wider range of users. So how does AMD shave hundreds of pounds off the cost of a GCN GPU?

Introducing Cape Verde

Radeon HD 7770 and HD 7750 are code-named Cape Verde. They'll slot-in just above the HD 6700-series that is actually based on venerable "Juniper" technology, as found on 2009's HD 5770.

Cape Verde GPUs are based on the GCN architecture first brought to market with the HD 7970, and you can gain a better understanding of how it works by heading on over to here. The transition from high-end, premium GPUs to mainstream parts is done by the age-old method of removing enough parts of the headline silicon as to make it economically feasible to produce at a lower price point.

To give you a precise view of where the cuts have taken place, and how large the cuts actually are, here's a detailed table breaking down the key specifications of the four available Radeon HD 7000-series GPUs, as well as two previous-generation cards that will be phased out shortly after the arrival of the HD 7770 and HD 7750.

Comparison discussion

Writing first from a pure GPU grunt perspective, the 28nm Cape Verde GPU features up-to 640 processors located within 10 Compute Units, 16 ROPs and a 128-bit memory interface. Compare this, absolutely unjustly, with the 2,048 processors, 32 CUs, 32 ROPs, and 256-bit interface of the top-of-the-line HD 7970 and it becomes clear that Cape Verde is a much, much less potent architecture than the range-heading "Tahiti." But, of course, you wouldn't expect a sub-£150 GPU to compete with the best, so would-be buyers can compare Radeon HD 7770 to Radeon HD 6850, and Radeon HD 7750 to Radeon HD 6770.

Performance speculation based solely on numbers doesn't paint Cape Verde in a particularly good light. The HD 7770, for example, has a lower single-precision GFLOPS rating than an HD 6770. It also has fewer processing cores and less bandwidth, too. However, on the flip side, the GCN architecture and a 28nm fabrication process enable an excellent power-draw figure of 80W.

Radeon HD 7750, meanwhile, loses two Compute Units - 128 cores - and reduces core frequency, although the 128-bit memory bus and 72GB/s of potential bandwidth remain intact, and both Cape Verde GPUs are outfitted with 1,024MB of GDDR5 as standard. What's impressive is that the Radeon HD 7750 is efficient enough to run without a dedicated PCIe power connector - it instead sources enough power through the PCIe bus.

AMD has used the bountiful frequency scaling of the 28nm GPUs and opted for a high core clock on the HD 7770, to offset the disadvantage created by having just 640 processing cores. Trumpeted with much fanfare, the default core clock is 1,000MHz, or a Gigahertz, and the word is AMD will be exploiting this seminal number with focussed marketing activity. Notwithstanding the attention-grabbing core frequencies, chances are that Radeon HD 7770 could be slower than an HD 5770/6770 in certain games.

GCN to the rescue

Yet it can be misleading to compare GPUs on a number-to-number basis. AMD reckons the general improvements in the GCN architecture, as used on Cape Verde, offer gaming improvements that aren't realised in a table like the one above. Citing the much-improved tessellation engine, high-occupancy throughput of the GCN core, lots of on-GPU cache, and PCIe 3.0 certification, Radeon HD 7770/50 may punch above their weight.

These 28nm GPUs also boast features that older GPUs cannot match. The Video Codec Engine (VCE) is a dedicated piece of logic that hardware-accelerates the encoding of H.264 content (1080p, 60fps) - much in the vein of Intel's Quick Sync - without really taxing other parts of the GPU.

Cape Verde GPUs also have six display outputs hardwired into the silicon, with the add-in board partner choosing how many to plumb out. Further, an improved HDMI specification, support for super-high-resolution displays, and ZeroCore power are forward-looking touches.

Is there room between the 7700-series and 7900-series?

The numbers are telling, and of course, AMD does have a 7800-series product line up its sleeve. Although no firm release date has been established, industry sources indicate that the first 7800-series GPUs - dubbed, most likely, the Radeon HD 7870 and HD 7850 - will arrive in March 2012. Armed with a GCN-based GPU code-named "Pitcairn," these cards are expected to the fill the sizeable gap between the £125 HD 7770 and £350 HD 7950.

Summary

AMD's Radeon HD 7770 and Radeon HD 7750 offer good performance across a wide range of games, and while architecture cuts suggest that framerate scores won't see a significant improvement over the previous generation, excellent tessellation performance, high-efficiency throughput and a multimedia feature-set that is absolutely cutting edge help position the cards as solid solutions at their respective price points.