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|
|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|
|Manufacturing process||TSMC, 55nm|
|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)|
|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 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|
|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.