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The cards
In its pure, unhindered form, Cape Verde can be found atop the Radeon HD 7770 GHz Edition. Well, atop the board itself, but under that deceptively large red-and-black cooling shroud and the tiny heatsink it conceals.

What you see above is the card AMD sent us. The company was squeamish about us taking pictures of it, because the sample doesn't have a shiny "GHz Edition" sticker on its cooling fan. Here's the picture AMD wanted us to show, instead:


Source: AMD

Yes, AMD is making quite a fuss over that "GHz Edition" moniker. We're not entirely sure why. The obvious reason is that the Radeon HD 7770 has a core clock speed of exactly one gigahertz, which leads AMD to tout it as the "the world's first GPU at 1GHz." But, see, that's not strictly true. Other cards have shipped with 1GHz core clocks in the past, and every Nvidia GPU since the GeForce 8800 series has run its shaders higher than the core speed. For several years now, most higher-end GeForces have run their shaders in the 1.5-2GHz range.

All of that is somewhat moot, though, because with any highly parallel processor—and especially with a GPU—clock speed is a very poor predictor of performance.

All you really need to know is that the "GHz Edition" label doesn't denote a particular variant of the Radeon HD 7770. All 7770s have a base clock of at least 1GHz, and some of AMD's board partners are offering even quicker variants. (More on that in a second.) The 7770 also features 1GB of GDDR5 memory pushing bits at 4500 MT/s. It draws 100W at most and 80W under typical gaming workloads, requires a lone six-pin PCIe power connector, and has a suggested e-tail price of $159.

Here's one of those faster variants we talked about: XFX's Radeon HD 7770 Black Edition. This bad boy runs at 1.12GHz, and its memory pushes an eye-popping 5200 MT/s. Its asking price is equally eye-popping: $179. That kind of money will buy you a nice Radeon HD 6870 nowadays, if you don't mind the larger power envelope, so this thing had better deliver.

At the other end of the spectrum lies the Radeon HD 7750, whose Cape Verde chip has had two of its compute units disabled. Since each compute unit has four texture units and four 16-wide vector units, the 7750 ends up with 512 shader ALUs and 32 texture units (down from 640 and 32, respectively, on the Radeon HD 7770). The 7750 is decidedly not a GHz Edition; it has a core clock speed of only 800MHz. However, its memory runs at the same speed as the 7770's, and both cards have the same 128-bit path to memory. Both offerings can also drive six monitors in an Eyefinity configuration, with the use of a DisplayPort hub... and provided you can find one of those.

The 7750's small sacrifices pay dividends in big ways. With a 75W max power envelope and 55W typical power draw, the card doesn't need a PCIe power connector, and it can get by with either a single-slot active cooler or a dual-slot passive one. (We're told Sapphire offers a passively cooled variant.) The 7750 is also, as you'd expect, quite a bit cheaper than its bigger brother, with a suggested e-tail price of only $109.

Ready to move on to the benchmarks? Not so fast. We have a big, meaty table full of peak theoretical numbers for you to pore over first:

  GPU core
clock
(MHz)
Peak pixel
fill rate
(Gpixels/s)
Peak bilinear
filtering
int8/FP16
(Gtexels/s)
Peak shader
arithmetic
(TFLOPS)
Memory
transfer
speed
(MT/s)
Memory
bandwidth
(GB/s)
GeForce GTS 450 783 13 25/25 0.6 3608 58
GeForce GTS 450 AMP! 875 14 28/28 0.7 4000 64
GeForce GTX 550 Ti 900 22 29/29 0.7 4104 98
GeForce GTX 550 Ti Cyclone 950 23 30/30 0.7 4306 103
GeForce GTX 460 1GB 675 22 38/38 0.9 3600 115
GeForce GTX 560 822 26 46/46 1.2 4008 128
Radeon HD 5770 850 14 34/17 1.4 4800 77
Radeon HD 5770 Super OC 900 14 36/18 1.4 4800 77
Radeon HD 6790 840 13 34/17 1.3 4200 134
Radeon HD 6850 775 25 37/19 1.5 4000 128
Radeon HD 6870 900 29 50/25 2.0 4200 134
Radeon HD 7750 800 13 26/13 0.8 4500 72
Radeon HD 7770 1000 16 40/20 1.3 4500 72
Radeon HD 7770 Black Edition 1120 18 45/22 1.3 5200 83
Radeon HD 7950 800 26 90/45 2.9 5000 240
Radeon HD 7970 925 30 118/59 3.8 5500 264

Judging by these theoretical figures, the Radeon HD 7770 has quite a bit more texture filtering power than the 5770. In fact, its filtering rates are close to those of the Radeon HD 6850. The 6850 does have somewhat higher peak shader performance, but Cape Verde's Graphics Core Next architecture should do a better job of living up to theoretical peaks than the 6850's VLIW5 design. It'll be interesting to see how close the 7770 ends up to the 6850 in real games.

To keep up with the 6850, the 7770 will have to overcome one serious handicap: its limited memory bandwidth. Not only does the 7700 have half the memory interface width of the 6850, but its memory speed is also lower than the 5770's. That leaves it with a comparatively paltry 72GB/s of bandwidth.

On the Nvidia front, the 7770 will have to contend with the GeForce GTX 550 Ti and the GTX 460 1GB. Making a prediction there is trickier. Both Nvidia cards have higher fill rates and more memory bandwidth, but they're both more limited when it comes to peak shader arithmetic. The 7700 has higher integer texture filtering performance, but the Nvidia cards can do FP16 filtering at the same speed, something the Radeon can't do.