The Intel QuickPath Interconnect or simply "QuickPath"[1][2] (the official legal name for Common System Interface or "CSI") is a point-to-point processor interconnect being developed by Intel, as a competitor to HyperTransport. QuickPath technology also includes an integrated memory controller.[3] It will replace the Front Side Bus (FSB) for Xeon and Itanium platforms. It is expected to be released in late 2008 and will first be used by Intel's Nehalem[4] and Tukwila[5] processors.
Performance numbers for QuickPath are reported to be 4.8 to 6.4 Gigatransfers per second (GT/s) per direction, and a link can be 5, 10 or 20 bits wide in each direction. Therefore the bandwidth provided by a full width link amounts to 12.0 to 16.0 GB/s per direction, or 24.0 to 32.0 GB/s per link.[6]
Initial Nehalem Implementation uses a 20-bit wide 25.6 GB/s link (as reported in the Intel Nehalem Speech on IDF). This 25.6 GB/s link provides exactly double the amount of theoretical bandwidth as Intel's FSB 1600 used in the X48 Chipset.
source:
http://en.wikipedia.org/wiki/Intel_QuickPath_Interconnect