TechPowerUp published a photo of the Socket AM4 platform demo motherboard that was showcased at AMD's pre-Computex press event. This board likely used one of the upcoming Bristol Ridge APUs.
The picture reveals a few big things about the AM4 socket, and the platform in general. To begin with, the 1331-pin PGA socket is somewhat the same size as AM3+, but likely features finer pins. It features CPU cooler retention holes in a "square" layout, rather than the rectangular layout that AMD has been using way back since socket 754. It will be interesting to see if these mount holes are compatible with any of Intel's sockets. The second and perhaps the biggest change of this platform, of course, is that the chipset is completely integrated with the processor, and so there's no chipset on the board. The processor socket wires out all the connections a southbridge, FCH, or PCH normally would, plus all the I/O of a northbridge (PCIe, memory, etc). The platform supports dual-channel DDR4 memory, and PCI-Express gen 3.0 across its PCIe budget.
WCCF Tech has a bit of extra information and says this motherboard is intended for a HP desktop PC, it reportedly uses the AMD A12-9800 APU. Bristol Ridge is basically an enhanced version of Carrizo, with the new Socket AM4, some new features like DDR4 support, higher performance and better integrated graphics. However, it seems there's some uncertainty about whether Bristol Ridge will get a big launch. The site speculates it could be an OEM-only platform.
Talking about Bristol Ridge, while the mobility platform has already been introduced, it’s time to talk about the desktop parts. The flagship A12-9800 processor comes with a core clock of 3.80 GHz. The chip features a quad core design along with 8 GCN 3.0 compute units, offering 512 stream processors. The processor is expected to feature a TDP around 65W (Configurable down to 45W). We can note in the following pictures that OEMs are readying desktop PCs with Bristol Ridge processors but the absence of AM4 boards from Computex may have indicated that Bristol Ridge could be an OEM only platform while Summit Ridge will bring AM4 to the masses.