So before we begin let's have a look at the two cards we'll be using in this test. From ATI we have their reference Radeon HD 4870 1024MB. It's the same card you receive when you purchase it in the store, as they hardly can be found customized or overclocked. It's an awesome little card though.
ATI Radeon HD 4850
ATI Radeon HD 4850 1GB
ATI Radeon HD 3850
ATI Radeon HD 4870
# of transistors
Stream Processing Units
2000 MHz GDDR3 (effective)
1980 MHz GDDR3 (effective)
1.66 GHz GDDR3 (effective)
3600 MHz GDDR5 (effective)
Math processing rate (Multiply Add)
As you guys know by now ATI's Radeon HD 4850/4870 are both using the same GPU (graphics processor). The codename for these chips is RV770. AMD put nearly a billion transistors into that GPU, which is now built upon a 55nm (260 mm2 Die size) production. The Radeon 4850/4870 series graphics processors have 800 scalar processors, if you are into this geek talk, you'll spot 10 SIMD clusters each carrying 80 32-bit Shader processors (this accumulates to 800). All these lovely little shader units like some memory bandwidth to work in, we call it VRAM, also known as video ram, aka frame buffer.
Since the 4870 series really digs that GDDR5 memory bandwidth, what's the cheapest thing to do to gain some extra performance? Increase the framebuffer volume. Now that by itself is not going to work miracles, yet in memory limited situations (loads of high quality textures, filtering and AA modes) it will help you here and there. This is where the 1024MB model has an advantage over the GeForce GTX 260 series, initially.
And a little bit of extra bite is all the product needs to get to fight that Core 216 card from NVIDIA. Here's the 1024MB Radeon HD 4870 that we are using today, gettin' warmed up in the test rig.