When AMD announced their brand new Radeon R9 290X flagship graphics card last week at their GPU 14 event many people noticed something missing from the cards. There were no CrossFireX connectors on the card. This is because AMD will be using new CrossFireX technology with the new Hawaii cards.
AMD (formerly ATI) has been using the CrossFire Bridge to facilitate multiple GPU configurations since the release of the X1900 series. Prior to this they were using the PCI-E bus for communications between two different graphics cards. By this time NVIDIA too had moved to SLI that allowed for more bandwidth than the PCI-E interface allowed.
It looks like AMD is returning to the bridge-less system for multi-GPU functionality as the PCI-E 3.0 bus has more than enough bandwidth for it. It has been confirmed by the slide you see above and VideoCardz that AMD will be using Sideport to enable multi-GPU configurations. This technology was actually originally set to debut with the Radeon 4870 X2, but it never happened. Anandtech has an article about the 4870 X2, which should give you some information about Sideport.
This technology allows for direct access between the GPU’s over PCI-Express so no external connectors are needed. This technology is fully compatible with AMD’s frame pacing technologies which help reduce pacing issues that are faced with multi-GPU setups. This has been a big concern with AMD’s 7000 series cards. AMD says that this new CrossFire technology for the R9 290X is designed for AMD Eyefinity and UltraHD (4K) resolution setups.