Overclocking The ATI Radeon HD 4870
The ATI Radeon HD 4870 is based on the long-awaited ATI RV770 GPU, which replaces the RV670 GPU that powered the disappointing ATI Radeon HD 3870 GPU. Both RV770 and the older RV670 are built on the same 55 nm fabrication process but that's where the similarity ends.
The Radeon HD 3870 has 320 stream processors and 16 texture units, delivering a fillrate of 12.4 gigatexels per second. It was also the first graphics card to feature DDR4 memory. Unfortunately, it was much too late and much too slow to pose much of a challenge to NVIDIA, much less a threat.
As alike they are in architecture and fabrication technology, the Radeon HD 4870 couldn't be more different from its predecessor. The performance boost it delivered was as revolutionary as its predecessor's was disappointing. This is literally the graphics card that ATI promised years ago and only just got around to delivering.
The ATI RV770 GPU that powers it has 800 stream processors and 40 texture units. That's 2.5X as many stream processors and texture units. The end result is a GPU with over 2.4X the fillrate of the RV670. In addition, the Radeon HD 4870 is the first graphics card to make use of GDDR5 memory. Unlike GDDR4, this new graphics memory is quad-pumped, literally delivering twice as much bandwidth at the same clock rate as GDDR4 or GDDR3 memory. The use of GDDR5 memory allowed the Radeon HD 4870 to deliver over 115 GB/s of memory bandwidth.
As we saw in our review of the ASUS EAH4870 Radeon HD 4870 graphics card, the Radeon HD 4870 was very much superior to high-end graphics cards like the NVIDIA GeForce 9800 GTX+. It was also about 2-2.5X faster than its predecessor, the Radeon HD 3870. Now, that is what you call a quantum leap ahead in performance!
Of course, this does not mean we are not going to try overclocking the card. Even though the Radeon HD 4870 will handily tackle practically every 3D game out there, there is still a dragon left to slay and that dragon is called Crysis. The Radeon HD 4870 delivered an average frame rate of 38 fps at 1600 x 1200 and 32 fps at 1920 x 1200. Very good but it would be nice to have better frame rates, wouldn't it? So, let's see how well the Radeon HD 4870 overclocks!
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 Radeon HD 4870 using its standard cooler.
The Radeon HD 4870 Cooler
Like all high-end graphics cards these days, the Radeon HD 4870 uses a thick GPU cooler that takes up two slots. The heatsink has a copper base with two copper heatpipes to draw the heat away to the aluminium fins.
A blower fan on the far end of the card sucks in ambient air, which is channeled by the shroud covering the heatsink to flow past the aluminium fins. The hot air is then exhausted out a row of vents located on the graphics card's bracket.
This is pretty much the standard fare for graphics cards of this range, so there's nothing particular special about this cooling method. It ain't fancy but it works!
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