HD7850: 1.76 TFLOPS, Engine Clock 860Mhz, 16 Compute Units (1024 Stream Processors), 64 Texture Units , 2/4GB GDDR5 with 153.6GB/s memory bandwidth

PS4 GPU: 1.84 TFLOPS, Engine Clock 800Mhz, 18 Compute Units (1152 Stream Processors), 72 Texture Units , 8GB GDDR5 with 176.0GB/s memory bandwidth (shared with CPU)

HD7870: 2.56 TFLOPS, Engine Clock 1000Mhz, 20 Compute Units (1280 Stream Processors) , 80 Texture Units , 2/4GB GDDR5 with 153.6GB/s memory bandwidth

http://www.extremetech.com/extreme/171375-reverse-engineered-ps4-apu-reveals-the-consoles-real-cpu-and-gpu-specs

As confirmed in the link above PS4 is a HD7870, not HD7850. What's really is going here is

They disabled 10% of the compute units for improving yields, and downclocked the GPU to avoid overheating and noise in a compact form factor. Let's do the math:

10% reduction in compute units give you

20*0.9 = 18 CUs

1280* 0.9 = 1152 Stream processors,

80*0.9 = 72 Texture Units,

In addition to that 20% decrease in operating frequency gives you

2.56 * 0.8 * 0.9 = 1.84 TFLOPS

So this is exactly an downclocked HD7870 with 10% disabled CUs BUT it has more bandwidth and a lot more fast RAM in addition to low level API excess, and standardized hardware. You cannot instantly expect miracles but this results in

a) Much lower CPU utilization (50-70% reduction)

b) More raw power (50-100% better performance)

c) Better optimization (more juice from the same hardware)

d) More stable performance

e) Better utilization of hardware due more and guaranteed bandwidth

f) More standardized future technologies

etc...

As a comparison, XB1 GPU is an underclocked 7790 with much slower memory (despite the fast esram). So the gap is larger than the simple comparison below.

http://www.hwcompare.com/14298/radeon-hd-7790-vs-radeon-hd-7870/

http://www.videocardbenchmark.net/gpu.php?gpu=Radeon+HD+7870&id=324

http://www.videocardbenchmark.net/gpu.php?gpu=Radeon+HD+7790&id=2502

More like an HD7860 since it runs between the two. Probably performs more like an OC 7850 than a 7870, obviously with more memory.

Performance depends but technically it IS a HD7870. It's the same GPU with different memory.

So slightly worse to on par with an entry level discrete GTX 760 which really is not bad for a console. Honestly though consoles only target 1080p so you don't need an earthshaking GPU. After a year when the PS4 has a good catalogue I may consider it as a third console. For those who have it, do you really need the subscription to play on-line? (frankly the biggest drawback I can see since I don't need backwards compatibility)

Interesting but after playing Ryse, a launch title, I'm content with what the X1 is capable graphically. The PS4 shoud dare better obviously.

I thought tech sites were saying the gpu in the xbox one was better? Or I mean sites are just throwing off the difference in power like it's the same as GC to Wii

It is... It have 20 CUs * the same than HD 7870 * but two are disabled for redundancies.

Obviously XB1 is quite capable and its performance will improve. But even with Ryse, it was not 1080p, it was not even stable 30 fps. Sure, all you want is this much graphics, it will be sufficient, but for more open world games, with richer and more detailed environments, this will be very limiting. I am not concerned about XB1's performance today, but more down the line in a few years ahead.

Are you sure you can legitimately pluralise 'site' in that sentence?