NVIDIA launched the GeForce GTX 280 and GTX 260 graphics cards on June 17, 2008. Both are based on the NVIDIA GT200 GPU which uses NVIDIA's improved, second-generation unified architecture. The new GT200 GPU, features amongst other things :

240 stream processors
Twice the number of registers
Fast local 16k shared memory (per cluster of 8 stream processors)
New texture scheduler
Double precision accuracy
3X ROP blending performance

For more information on the NVIDIA GT200 GPU, please take a look at the NVIDIA GTX 280 & GTX 260 Technology Report.

As we saw it our review of the ASUS ENGTX280 TOP graphics card, the standard GeForce GTX 280 is roughly equivalent to the ATI Radeon HD 4870. That's why GeForce GTX 280 is now priced at the same level as the Radeon HD 4870. Only the factory-overclocking of the ASUS ENGTX280 TOP allowed it to deliver a significant performance advantage over the Radeon HD 4870.

Fortunately, the NVIDIA GeForce GTX 280 is pretty overclockable. The ASUS ENGTX280 TOP came factory-overclocked by 11.3% (core) and 9.8% (memory) but there was still some room left for further overclocking. Best of all, NVIDIA provided all the necessary tools for easy overclocking, with complete access to core and memory clocks as well as fan speed. So, we just had to try overclocking it to see how far it can go!

Like in our previous overclocking guides, we did not want this to be an example of extreme overclocking, where you would need to resort to third-party coolers. With that method, you can achieve an incredible degree of overclocking but it would come at a significant cost. We wanted this attempt to come at "no cost" to the user. That meant overclocking the GeForce GTX 280 using its standard cooler.

Source: http://www.techarp.com/showarticle.aspx?artno=617