AMD have revealed that they're working on a hexacore - or six-core - processor for release in 2010. The chip, codenamed Thuban, will be manufactured using 45nm processes and have an integrated DDR3 controller; more interestingly, however, it will be backward compatible with existing AM2+ and AM3 motherboards.
The chip has not yet been officially named - or at least AMD aren't telling - but is expected to be known as the Phenom II X6. It will also likely have 3MB of L2 and 6MB of L3 cache, and begin with lower clock speeds than the existing quad-core chips thanks to the extra heat produced. It's unlikely that the AMD Thuban processors will reach the market ahead of Intel's Core i9 chips.