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Review: Double trouble: Sapphire Radeon HD 4670 in CrossFire

by Tarinder Sandhu on 12 September 2008, 09:02

Tags: Radeon HD 4670 512MB, ATI Radeon HD 4670, AMD (NYSE:AMD), Sapphire, ATi Technologies (NYSE:AMD), PC

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Is two better than one?

Let's do some architecture comparisons and try to shed some light on to whether the Radeon HD 4670, run in two-board CrossFire, stands a chance against Radeon HD 4850.

Please note the stated CrossFireX figures, shown in column two, are for two Radeon HD 4670 boards.

Graphics cards ATI Radeon HD 4670 GDDR3 ATI Radeon HD 4670 GDDR3 XF ATI Radeon HD 4850 GDDR3
PCIe PCIe 2.0
GPU clock 750MHz 750MHz 625MHz
Shader clock 750MHz 750MHz 625MHz
Memory clock (effective) 2,000MHz 2,000MHz 2,000MHz
Memory interface, size, and implementation 128-bit, 512MB GDDR3 256-bit, 1,024MB, GDDR3 256-bit, 512MB, GDDR3
Memory bandwidth 32GB/sec 64GB/sec 64GB/sec
Manufacturing process TSMC, 55nm
Transistor count 514M 1,028M 965M
Die size 146mm² 292mm² 260mm²
DirectX Shader Model DX10.1, SM4.1
Vertex, fragment, geometry shading (shared) 320 FP32 scalar ALUs, MADD dual-issue (unified) 640 FP32 scalar ALUs, MADD dual-issue (unified) 800 FP32 scalar ALUs, MADD dual-issue (unified)
Peak GFLOP/s 480 960 1,000
Data sampling and filtering 32ppc address and 32ppc bilinear INT8 filtering (16ppc FP16), max 16xAF 64ppc address and 64ppc bilinear INT8 filtering (32ppc FP16), max 16xAF 40ppc address and 40ppc bilinear INT8 filtering, (20ppc FP16) max 16xAF
Peak GTexel/s (bilinear) 24 48 25
Peak GPixel/s 6 12 10
ROPs 8 16 16
Peak TDP (claimed) 59W 108W 110W
Power connectors (default clock) None None 6-pin
Multi-GPU CrossFireX - four-board CrossFireX  CrossFireX four-board
Outputs (native) 2 x dual-link DVI w/HDCP, DisplayPort, HDMI 7.1-channel
Hardware-assisted video-decoding engine AMD UVD 2 - full H.264 and VC-1 decode
Reference cooler single-slot single-slot single-slot
Retail price (default-clocked model) £50-£55 £100-£110 £110-£125

What do you know: Radeon HD 4670 two-card CrossFire stacks up quite nicely against single-GPU Radeon HD 4850.

Overall memory bandwidth is the same. The math throughput is also very similar, with clock-speed making up for shader-count. The transistor-count and, to an extent, die-size and pricing are all pretty close, too.

Radeon HD 4670 XF has the edge in filtering, being endowed with a better shading-to-texturing ratio than HD 4850.

Power-draw, too, is eerily similar, and the non-3D feature-set is, for all intents and purposes, identical.

So, should the budget CrossFired pair be faster than a single-GPU '4850? The answer is yes and no. Pure on-paper specifications would lead us to believe that it can be, but the vagaries of multi-GPU rendering mean that linear increases are not always observed in games.

Seeing double? You bet.