The six-core Istanbul processor has begun shipping, and variants focusing on differing levels of power and performance – the HE, SE, and EE versions – will begin shipping by the third quarter…

The Istanbul, uses HyperTransport links to connect the microprocessor cores to eliminate processing bottlenecks. Another technology, called “HT Assist,” uses part of the level-3 cache as a type of look-up table, eliminating the need to poll each microprocessor when making a cache request for a particular piece of data. Instead, the core only needs to poll one other to find the data’s location.

AMD Ships Six-Core ‘Istanbul’ Server Chip – News and Analysis by PC Magazine

It uses DDR2 still while Intel’s chip uses the faster (costlier) DDR3.