As I start to write, we’re ripping apart the Sony CXD90026G die to try and get a floorplan and see what’s in there.
However, before we get to that, let’s have a closer look at what was in the box. Underneath the mother board was a piece of tinplate with numerous holes cut in it, covering the fan and the heat sink. There’s a square hole visible with a blob of heat-conducting goop in it, and we can see the impression of the CPU chip in the goop. The goop itself is on the bottom of the heat sink, mounted on the other side of the tinplate. That’s a hefty heat sink, we haven’t seen one like that since we pulled an IBM server apart. I guess with a maximum rated power of 250 W for the system, its needed! So it’s no surprise that the chip was mounted directly against the heat sink, and that it has a good chunk of metal around it to help with heat dissipation.
Now we’ve got it off the board, we have the die size more accurately measured as 19.0 x 18.3 mm (348 sq mm). That’s a pretty huge die, especially compared with the total chip area of 228 sq mm for the CPU and GPU devices in the last PS3 that we looked at. And we’ve also gone from 40/45-nm processes to TSMC’s 28-nm process, so there is a lot more functionality here. Sony has switched from chips based on the IBM Cell eight-core processor to AMD’s Jaguar cores, still with eight cores, and incorporated the GPU into the same silicon die.
According to Anandtech the GPU has 18 “Compute Units” comprising 1152 shader processors/cores/ALUs (whatever you want to call them), capable of running at 1.84 TFLOPS, or in between a Radeon HD 7850 and 7870 plug-in GPU. If we look at the specs of those, they can draw 150 – 190 W on their own, so a huge proportion of the power is devoted to the graphics processing. AMD states that the Jaguar core is ~3.1 sq mm, so with eight cores that’s ~25 sq mm, or about 7% of the die area, although that does not include up to 4 MB cache (four cores can share up to 2 MB in the Jaguar architecture).
As it happens, we looked at a Radeon HD 7970 GPU chip last year, also fabbed on TSMC’s 28-nm process, and a Compute Unit takes up ~3.7 sq mm plus ~1.8 sq mm L1 and L2 cache, making the GPU part of the Sony chip ~88 sq mm (25%).
Now we have the transistor level die image, and our first draft of the floor plan - we can see the eight CPU cores, but we count twenty graphics cores/compute units. Possibly two are redundant to improve yield - this is a big die, after all! The memory I/Os seem to be wrapped aroundthree sides of the die to match the layout of the GDDR5 memory chips on the motherboard. The graphics cores are a slightly different layout, but the same size as the Radeon part, at ~5.6 sq mm, and the Jaguar cores, including cache, are ~6.5 sq mm each; making the GPU 33% of the chip area, and the cpu cores 15%.
The cross-section shows eleven copper metal layers, plus a top level aluminum not in the image. If we zoom in on the transistors we can see that they are using TSMC's 28-nm high-k, metal gate process, likely the 28HP variant used for the Radeon GPUs.
That just about wraps up what we can find out about Sony's latest processor in one day. Seeing as our guys were queuing to buy the PS4 only this morning, that's pretty good going - thanks to all here for the great work they've done!