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AMD Radeon HD 6870 and 6850 review

by Tarinder Sandhu on 22 October 2010, 03:00 4.5

Tags: AMD (NYSE:AMD), Sapphire, HiS Graphics

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The Table of Doom

Graphics cards ATI Radeon HD 5870 1,024MB ATI Radeon HD 5850 1,024MB ATI Radeon HD 5830 1,024MB ATI Radeon HD 6870 1,024MB ATI Radeon HD 6850 1,024MB NVIDIA GeForce GTX 480 1,536MB NVIDIA GeForce GTX 470 1,280MB NVIDIA GeForce GTX 465 1,024MB NVIDIA GeForce GTX 460 1,024MB NVIDIA GeForce GTX 460 768MB
Transistors 2.15bn 2.15bn 2.15bn 1.75bn 1.75bn 3.0bn 3.0bn 3.0bn 1.95bn 1.95bn
Die size 334mm² 334mm² 334mm² 255mm² 255mm² 529mm² 529mm² 529mm² 368mm² 368mm²
General clock 850MHz 725MHz 800MHz 900MHz 775MHz 700MHz 607MHz 607MHz 675MHz 675MHz
Shader clock 850MHz 725MHz 800MHz 900MHz 775MHz 1,401MHz 1,215MHz 1,215MHz 1,350MHz 1,350MHz
Memory clock  4,800MHz 4,000MHz 4,000MHz 4,200MHz 4,000MHz 3,696MHz 3,348MHz 3,206MHz 3,600MHz 3,600MHz
Memory interface and size 256-bit, 1,024MB, GDDR5 256-bit, 1,024MB, GDDR5 256-bit, 1,024MB, GDDR5 256-bit, 1,024MB, GDDR5 256-bit, 1,024MB, GDDR5 384-bit, 1,536MB GDDR5 320-bit, 1,280MB GDDR5 256-bit, 1,024MB GDDR5 256-bit, 1,024MB, GDDR5 192-bit, 768MB, GDDR5
Memory bandwidth 153.6GB/s 128GB/s 128GB/s 134.4GB/s
128GB/s 177.4GB/s 133.9GB/s 102.6GB/s
Shaders 1,600 1,440 1,120 1,120 960 480 448 352 336 336
 GFLOPS  2,720
2,088 1,792 2,016 1,488 1,345 1,089 855
Texturing 80ppc bilinear
40ppc FP16
72ppc bilinear
36ppc FP16
56ppc bilinear
28ppc FP16
56ppc bilinear
28ppc FP16
48ppc bilinear
24ppc FP16
60ppc bilinear
30ppc FP16
56ppc bilinear
28ppc FP16
44ppc bilinear
22ppc FP16
56ppc bilinear
28ppc FP16
56ppc bilinear
28ppc FP16
ROPs 32
32 16 32 32 48
GPixels/s  27.2 23.2 12.8 28.8 24.8 33.6
GTexel/s bilinear 68
52.2 44.8 50.4
37.2 42
Board power (max) 188W 151W 175W 151W 127W 250W 215W 200W 160W 150W
Multi-GPU Four-way XFire Four-way XFire Four-way XFire Two-way XFire Two-way XFire Three-way SLI Three-way SLI Three-way SLI Two-way SLI Two-way SLI
Board length 11in 9.5in 11in 9.5in 9in 10.5in 9.5in 9.5in 8.25in 8.25in
Outputs 2x dual-link DVI
HDMI, DisplayPort, 
2x dual-link DVI
HDMI, DisplayPort, 
2x dual-link DVI
HDMI, DisplayPort, 
HDMI, 2x DisplayPort, 
HDMI,  2x DisplayPort, 
2x dual-link DVI
2x dual-link DVI
2 x dual-link DVI Mini-HDMI 2 x dual-link DVI Mini-HDMI 2x dual-link
Retail price  £295  £215 £165 £189+ £150+ £360  £200
Analysis: Radeon HD 6870 1,024MB

Discussions on architecture are somewhat moot without a good look at the speeds and feeds. Let's put the Radeon HD 6870 into context by looking directly at the Radeon HD 5870.

First off, as we have indicated previously, Radeon HD 6870 is a significantly smaller chip. The transistor-count drops by almost 20 per cent and the die is reduced by almost 25 per cent. What this means is that, ceteris paribus, the HD 6870 is plain cheaper to produce on the same 40nm process as Radeon HD 5870, and this fact is the main reason why the Radeon HD 6870 will be a little cheaper than the Radeon HD 5850 and HD 5870 cards.

Jumping around the table, a smaller die leads to lower power-draw, down from 188W to 151W. Pragmatically, while HD 6870 still requires two six-pin PCIe connectors, coolers will be in the same vein as the HD 5850.

Shading power is much lower on HD 6870, though, as it's equipped with 1,120 stream processors - the same as HD 5830 - clocked in at 900MHz. The math tells us that it faces a 25 per cent deficit when up against HD 5870 in this regard. The good news is that the high core frequency and a Cypress-matching 32 ROPs keep pixel throughput at decent levels, while texture throughput is also more like HD 5850 - both share a GPU-wide 56 units.

Memory bandwidth sits between HD 5870 and HD 5850, so on paper, without factoring in the benefits of an improved tessellation engine and other minor AA/AF performance-related tweaks, one would surmise that it should benchmark between the two HD 5800-series cards. Should that indeed be the case, a retail price of £190, once the furore of launch-day pricing dies down, will make it a solid proposition.

Analysis: Radeon HD 6850 1,024MB

The Radeon 6850 card should arrive with a retail price of around £150. Based on the same core as the HD 6870, the cheaper GPU drops shaders from 1,120 to 960 - 14 SIMD engines to 12 - reduces the core frequency from 900MHz to 775MHz, and memory speed from 4.2GHz to 4.0GHz.

Add the numbers up and a sensible guesstimate predicts that HD 6850 will provide around 85 per cent of the performance of its bigger brother. The positive trade-off here is a lower street price, obviously, but also a lower card TDP - down to 127W - enabling AMD to get away with using a single six-pin PCIe connector.

Conjecturing before we see the benchmarks, the HD 6850 should beat the HD 5830 with ease and, looking at the other side, give the GeForce GTX 460 1,024MB GPU a good go.

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