The site writes there will be three Radeon 4800 series models: the 4850, 4870 and 4870 X2. The Radeon 4850 is the launch model and it will feature 512MB GDDR3 memory but there will also be a cheaper 256MB version for OEMs and system integrators. The Radeon 4850 is codenamed "Makedon", the card has CrossFire X support for up to four graphics cards, it will use a single-slot cooling solution and will require a single 6-pin PCI Express power connector. Pricing of the 4850 should be around $189-$219.
In July the firm will release the Radeon 4870 512MB GDDR5 and 4870 X2 1024MB GDDR (R700). The Radeon 4870 is codenamed "Trojan" and will feature a dual-slot cooler. Rumour has it that the 4870 will perform on par or slightly better than a Radeon HD 3870 X2 graphics card. The 4870 will likely cost $249 to $279 but it's possible that AMD will try to go for $199 to $249 to grab more marketshare.
Also interesting is that the Radeon 4800 series is rumoured to have some kind of physics acceleration:
Looking at features, ATI will promote DirectX 10.1, PCI Express 2.0, dynamic geometry acceleration and other functions that were introduced with the Radeon 3800 series. What surprises us is that the manufacturer is highlighting a "Game physics processing capability" in its launch materials. Since ATI didn't bid for Havok (which ended up in Intel’s lap) and Nvidia snapped up PhysX we wonder who provides a physics engine for ATI. Perhaps the company took a completely different direction and it simply expanded its GPGPU capabilities from professional FireStream cards to the desktop.
The Radeon 4800 series also includes 7.1 channel-via-HDMI support and color output also got a “significant” boost, our sources said. We were unable to confirm HDMI 1.3 support, but we would not be surprised if that in fact is the case. The Unified Video Decoder is now in generation 2 and is called "UVD2".