http://xbox360.ign.com/articles/636/636018p3.html

這幾天有傳出一些Developer對C1的印象。
Beta kit目前似乎是90%的時脈….
然後，大約是alpha kit(x850xt?)的兩倍效率。

原文：

One North American developer had this outlook.

"On our side, we’ve been working very hard to tap into the full power of the Betas. On a technical side, while the GPU is nearly twice as powerful as the Alpha kits, the CPU architecture requires very clean logic coding in order to take advantage of its full potential." (We’ll get to the clean logic bit later on in the story.)

Another developer explained the differences this way:

"The major difference is in the video chipset, which is pretty different from anything you can find on the PC (or alpha hardware). It does some slick bits of load balancing between pixel performance and vertex performance, which helps us make sure that we’re maxing out the video hardware no matter what we’re doing. HDTV looks spectacular on this thing.

雖然沒有提到"兩倍"的詳細狀況，不過可以推論一下：
如果都有開FSAA的話，考慮X850XT在4AA8AF大約是noAAnoAF的70%效率，以及C1的4x FSAA有95%的效率，可以得知C1的fillrate(or Shader Power)大概是R4x0的1.4~1.5倍。

也就是說，幾乎同時脈下，C1的ALU數量超過R4x0的兩倍(6+16 vs 48)，但是看起來只有70～80%的效率….這樣好像有點虧？

話說回來，R520的效率應該會比C1好些。
首先，R520一直有消息指出是vs/ps分離式設計，這是效率較好但是靈活度較差的設計。
二來R520在PCWatch提過，可使用的thread數量較大，代表R520結構內的bank數理應較C1為大，有著較少的ALU數量與較大的bank數，代表每bank的ALU數量勢必大幅減少。
(個人認為4ALU per bank、8bank total的可能性為大；不過ATI公開了這個數字，代表developer可以控制thread，應該就代表R520是US結構？)

——–
總之，基本上US的效率較低是合理的，畢竟G80看來都打算用兩倍左右的時脈去補了….
或許這只是告訴我們，天下終究沒有白吃的午餐罷了。