The AMD Fiji GPU

AMD Fiji

So, over the past two years you have been hearing about several codenames and that can be a little confusing. AMD likes to stick to island series GPUs for their product codenames, for the Fury PRO and XT GPU series the GPU gets its Fiji denomination from there. AMD Fiji is the new GPU used, we are going to talk about the GPU now and through part of the next page we'll talk a little more in-depth about the HBM that sits on that GPU.

If you haven't seen the photos from our previous Fiji articles hey, meet Fiji:
 

At an AMD event I was able to snag two Fiji chips. Look at that, the GPU core surrounded by the four stacks of HBM memory. These puppies are roughly 5x5cm each.

The Fiji series of GPUs is the next iteration of the GCN (Graphics Core next) architecture. Fiji is based on GCN version 1.2 revision 3. Basically, if we take Tonga (radeon R9 280/380) and scale that upwards in multitudes that would be Fiji (but that is an overly generalized explanation).

Fiji is still based on a 28nm fabrication node, 20nm failed and until we see 16 and 14nm viable for big GPUs, the 28nm node really is the only alternative. That was the same dilemma for Nvidia with the GTX 980 Ti of course. Both GPUs, as a result, are big. For Fiji that Mac Daddy is 5x5cm in size. Bigger means higher voltage usage, and thus more heat to deal with. You can only imagine what a chip like this would be like on 14nm, at half the size. AMD did huge things with Fiji though, they tucked away 8.9 Billion transistors on the GPU and that's the number without the memory. It gives them a staggering 8.6 TFLOPS of performance to work with. That, combined with HBM memory, is to be considered serious stuff. The GPU has a whopping amount of transistors. At 28nm AMD applied the GCN 1.2 architecture, albeit you will learn that there have been a few tweaks at cache level as the L2 cache is now 2MB for example.

	AMD Radeon R9 Fury X	AMD Radeon R9 Nano	AMD Radeon R9 390X
Fabrication Process	28nm	28nm	28nm
GPU	Fiji	Fiji	Hawaii / Grenada
Streaming Processors	4096	4096	2816
Graphics memory	4 GB HBM	4 GB HBM	8 GB GDDR5
Memory Clock	up-to 500 MHz / 1.0 Gbps	up-to 500 MHz / 1.0 Gbps	6.0 Gbps
Core Clock	1050 MHz	up-to 1000 MHz	1050 MHz
Memory Bandwidth	up-to 512 GB/s	up-to 512 GB/s	384 GB/s
Power Connectors	2 x 8-pin	1 x 8-pin	1 x 6-pin - 1 x 8-pin
Form Factor	Full Height, Dual slot	Full Height, Dual slot	Full Height, Dual slot
Freesync	Yes	Yes	Yes
DirectX 12 Support	Yes	Yes	Yes

An interesting step from AMD is the move towards a 4096-bit memory bus thanks to HBM. Nobody really expected it as in the past AMD merely placed GDDR on their products. You will notice very similar structures compared to Tonga (Radeon R9 265 and 380). This is GCN 1.2, yet multitudes of it. The Fiji GPU as such has 4096 shader processors, these are clustered up in groups of 64 shader processors per CU (compute unit). 64 units times 64 shaders = 4096.

The 1000 MHz core clock frequency is not a fixed clock on the NANO. In almost all scenarios we have seen it hovers in the 900 MHz range. Basically, if the card passes its power limitations or gets too warm then the card will clock up/down in-between these monitored limiters.