Istanbul is a pretty straight forward socket upgrade over AMDs current Shanghai Opterons. A 45nm processor with 6 MB of L3 cache that fits into a Socket-F style mainboard, only now with six cores rather than Shanghai’s four cores. The end result is that Istanbul will provide a direct drop-in upgrade for existing Socket-F systems without the need to change major components or perform software upgrades/changes.
AMD had originally stated that Istanbul processors would become available in the second half of this year (2009), however no other information has been released as to exactly when we could expect to see them becoming publicly available. Though, with the recent working demonstration of Istanbul, it may be safe to say that we could expect them slightly earlier than originally projected.
AMD demonstrated the Istanbul six-core and ran an identical Shanghai system beside it and performed Stream based benchmarks, both with HyperTransport 3 active (note that HyperTransport 3 is not currently available in shipping Shanghai products). The Shanghai system configured with 16-cores produced a throughput in the range of 25,000 MB/sec. while the 24-core Istanbul configuration produced about 42,000 MB/sec.. That is nearly double the performance gained by the addition of only fifty-percent more cores.
This gain in performance is attribued to a feature AMD calls a probe filtering or properly put, a snoop filtering, which functions to reduce traffic on socket-to-socket HyperTransport links by storing an index of all caches and preventing unnecessary coherency synchronization requests. Current Opterons use a broadcast-based probe protocol, sending probe requests to all sockets.
AMD is currently planning a full lineup of six-core Opterons based on Istanbul including low-power HE versions and high-performance SE models, all within customary Opteron power and thermal envelopes.