16 IBM eX5 Implementation Guide2.1 eX5 chip setThe members of the eX5 server family are defined by their ability to use IBM fifth-generationchip sets for Intel x86 server processors. IBM engineering, under the banner of EnterpriseX-Architecture (EXA), brings advanced system features to the Intel server marketplace.Previous generations of EXA chip sets powered System x servers from IBM with scalabilityand performance beyond what was available with the chip sets from Intel.The Intel QuickPath Interconnect (QPI) specification includes definitions for the followingitems: Processor-to-processor communications Processor-to-I/O hub communications Connections from processors to chip sets, such as eX5, referred to as node controllersTo fully utilize the increased computational ability of the new generation of Intel processors,eX5 provides additional memory capacity and additional scalable memory interconnects(SMIs), increasing bandwidth to memory. eX5 also provides these additional reliability,availability, and serviceability (RAS) capabilities for memory: Chipkill, Memory ProteXion, andFull Array Memory Mirroring.QPI uses a source snoop protocol. This technique means that a CPU, even if it knowsanother processor has a cache line it wants (the cache line address is in the snoop filter, andit is in the shared state), must request a copy of the cache line and wait for the result to bereturned from the source. The eX5 snoop filter contains the contents of the cache lines andcan return them immediately. For more information about the source snoop protocol, see2.2.4, “QuickPath Interconnect (QPI)” on page 18.Memory that is directly controlled by a processor can be accessed faster than through theeX5 chip set, but because the eX5 chip set is connected to all processors, it provides lessdelay than accesses to memory controlled by another processor in the system.2.2 Intel Xeon 6500 and 7500 family processorsThe IBM eX5 servers use the Intel Xeon 6500 and Xeon 7500 family of processors tomaximize performance. These processors are the latest in a long line of high-performanceprocessors: The Xeon 6500 family is used in the x3690 X5 and BladeCenter HX5. These processorsare only scalable to up to two processors. This processor does not support the ability toscale to multiple nodes; however, certain models support MAX5. The Xeon 7500 is the latest Intel scalable processor and can be used to scale to two ormore processors. When used in the IBM x3850 and x3950 X5, these servers can scale upto eight processors. With the HX5 blade server, scaling up to two nodes with fourprocessors is supported.Table 2-1 on page 17 compares the Intel Xeon 6500 and 7500 with the Intel Xeon 5500 and5600 processors that are available in other IBM servers.
